HON INTR ATMOSPHERE
HON INTR ATMOSPHERE MET 1010
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mm mm F mv mm mm F mv sum nibdz an1W wt mm a an x m 1 quotmm mum um um un mm P m m mm quotmom 4 mm 39 munhi mumquot uy m quotmmquot mm mm F m ldi 147 million km i 152 million km gt imam guy amen7N aphelion 7 July mm mm F mv s Tr11 xrauuap 7l mm w W m a 4 nmdgmwyrg anmw n BSeasons mm mum WEE v 4 murmur lav mm mm P m US DEPARTMENT OF COMMERCE NATIONAL OCEANIC AND ATMOSPHERIC ADMINISTRATION NATIONAL WEATHER SERVICE S I I C I S US DEPARTMENT OF TRANSPORTATION FEDERAL AVIATION ADMINISTRATION Revised December 1999 FOREWORD AC 0045E Aviation Weather Services is published jointly by the Federal Aviation Administration and the National Weather Service NWS This document supplements the companion manual AC 006A Aviation Weather that deals with weather theories and hazards This advisory circular AC 0045E explains weather service in general and the details of interpreting and using coded weather reports forecasts and observed and prognostic weather charts Many charts and tables apply directly to ight planning and in ight decisions It can also be used as a source of study for pilot certi cation examinations The AC 0045E was written primarily by Kathleen Schlachter with contributions from Jon Osterberg Doug Streu and Robert Prentice A special thanks to Sue Roe for her help and patience in editing this manual Comments and suggestions for improving this publication are encouraged and should be directed to National Weather Service Coordinator WSR64 Federal Aviation Administration Mike Monroney Aeronautical Center PO Box 25082 Oklahoma City OK 731250082 Advisory Circular AC 0045E supersedes AC 0045D Aviation Weather Services revised 1995 TABLE OF CONTENTS Section 1 THE AVIATION WEATHER SERVICE PROGRAM National Oceanic and Atmospheric Administration NOAA ll Federal Aviation Administration FAA 13 Obse atinn 18 Communications Systems llO U er 11 0 Section 2 AVIATION ROUTINE WEATHER REPORT METAR Type of Report 21 ICAO Station Identi er 22 Date and Time of Report 23 Modi er As Required 23 Wind 24 Visibility 25 Runway Visual Range RVR As Required 26 Weather Phenomena 26 Sky nnditinn 210 TemperatureDew Point Group 219 Altimeter 219 Remarks RMK As Required 220 Section 3 PILOT AND RADAR REPORTS SATELLITE PICTURESAND RADIOSONDE ADDITIONAL DATA RADATs Pilot Weather Reports PIREPs 31 Radar Weather Reports SDs 36 Satellite Weather Pictures 311 Radiosonde Additional Data RADATs 315 Section 4 AVIATION WEATHER FORECASTS Aviation Terminal Forecast TAF 41 Aviation Area Forecast FA 417 In ight Aviation Weather Advisories 423 Alaska Gulf of Mexico and International Area Forecasts FAs 427 Transcribed Weather Broadcast TWEB Text Products 431 Winds and Temperatures Aloft Forecast FD 435 Center Weather Service Unit CWSU Products 438 Hurricane Advisory WI I 440 Convective Outlook AC 441 Severe Weather Watch Bulletins WWs and Alert Messages AWWs 442 Section 5 SURFACE ANALYSIS CHART Valid Time 51 Isobars 51 Pressure Systems 51 Fronts 51 Troughs and Ridges 51 Other I f quot 52 Using the Chart 52 Section 6 WEATHER DEPICTION CHART Plotted Data 61 Analvsis 64 Using the Chart 64 Section 7 RADAR SUMMARY CHART Echo P 391 quot quot Type 7l Intensity 72 Echo Con guration and Coverage 72 Echo Tnps 73 Echo 73 Severe Weather Watch Areas 73 Using the Chart 73 Section 8 CONSTANT PRESSURE ANALYSIS CHARTS Plotted Data 81 Analvsis 81 ThreeDimensional Aspects 83 Using the Charts 83 Section 9 COMPOSITE MOISTURE STABILITY CHART Stability Panel 91 P 391 quot 39 39 Water Panel 94 Freezing Level Panel 95 Average Relative Humidity Panel 99 Using the Chart 910 Section 10 WINDS AND TEMPERATURES ALOFT CHART Forecast Winds and Temperatures Aloft FDI Observed Winds Aln Using the Charts International Flights SECTION 11 SIGNIFICANT WEATHER PROGNOSTIC CHARTS US LowLevel Signi cant Weather Sig WX Prno 36 and 48Hour Surface Prno HighLevel Signi cant Weather Prno 101 103 103 104 111 115 116 Section 12 CONVECTIVE OUTLOOK CHART Day 1 Convective Outlook Day 2 Convective Outlook Levels of Risk Using the Chart Section 13 VOLCANIC ASH ADVISORY CENTER PRODUCTS Volcanic Ash Advisory Statement VAAQ 122 131 Volcanic Ash Forecast Transport And Dispersion Chart VAF TAD VAFTAD Product 132 133 Using the Chart Section 14 TURBULENCE LOCATIONS CONVERSION AND DENSITY ALTITUDE TABLES CONTRACTION S AND ACRONYMS SCHEDULE OF PRODUCTS NATIONAL WEATHER SERVICE STATION IDENTIFIERS WSR 88D SITES AND INTERNET ADDRESSES Locations of Probable Turbulence 133 141 Standard Conversion Table 143 Density Altitude 144 Contractions and Acronyms 146 Scheduled Issuance and Valid Times of Forecast Products National Weather Service Station Identi ers WSR 88D Sites Internet Addresses 1420 1421 1423 1425 December 1999 Section 1 THE AVIATION WEATHER SERVICE PROGRAM Providing weather service to aviation is a joint effort of the National Weather Service NWS the Federal Aviation Administration FAA the Department of Defense DOD and other aviationoriented groups and individuals This section discusses the civilian agencies of the US Government and their observation and communication services to the aviation community NATIONAL OCEANIC AND ATMOSPHERIC ADMINISTRATION NOAA The National Oceanic and Atmospheric Administration NOAA is an agency of the Department of Commerce NOAA is one of the leading scienti c agencies in the US Government Among its six major divisions are the National Environmental Satellite Data and Information Service NESDIS and the NWS NATIONAL ENVIRONMENTAL SATELLITE DATA AND INFORMATION SERVICE NESDIS The National Environmental Satellite Data and Information Service NESDIS is located in Washington DC and directs the weather satellite program Figures 32 and 33 are examples of Geostationary Operational Environmental Satellite GOES images These images are available to NWS meteorologists and a wide range of other users for operational use Satellite Analysis Branch SAB The Satellite Analysis Branch SAB coordinates the satellite and other known information for the NOAA Volcanic Hazards Alert program under an agreement with the FAA SAB works with the NWS as part of the Washington DC Volcanic Ash Advisory Center VAAC NATIONAL WEATHER SERVICE NWS The National Weather Service NWS collects and analyzes meteorological and hydrological data and subsequently prepares forecasts on a national hemispheric and global scale The following is a description of the NWS facilities tasked with these duties National Centers for Environmental Prediction NCEP There are nine separate national centers under National Centers for Environmental Prediction NCEP each with its own speci c mission They are the Climate Prediction Center Space Environment Center Marine Prediction Center Hydrometeorological Prediction Center Environmental Modeling Center NCEP Center Operations Storm Prediction Center Aviation Weather Center and the Tropical Prediction Center National Center Operations NCO Located in Washington DC the National Center Operations NCO is the focal point of the NWS s weather processing system From worldwide weather reports NCO prepares automated weather analysis charts and guidance forecasts for use by NWS of ces and other users December 1999 Some NCO products are specifically prepared for aviation such as the winds and temperatures aloft forecast Figure 49 is the network of forecast winds and temperatures aloft for the contiguous 48 states Figure 410 shows the Alaskan and Hawaiian network NCO is part of VAAC which runs an ash dispersion model NCO works with SAB to fulfill the VAAC responsibilities to the aviation communities regarding potential volcanic ash hazards to aviation Storm Prediction Center SPC The Storm Prediction Center SPC is charged with monitoring and forecasting severe weather over the 48 continental United States Its products include convective outlooks and forecasts as well as severe weather watches The center also develops severe weather forecasting techniques and conducts research The SPC is located in Norman Oklahoma near the heart of the area most frequently affected by severe thunderstorms Hydrometeorological Prediction Center HPC The Hydrometeorological Prediction Center HPC prepares weather charts which include basic weather elements of temperature fronts and pressure patterns Aviation Weather Center AWC The Aviation Weather Center AWC located in Kansas City Missouri issues warnings forecasts and analyses of hazardous weather for aviation interests The center identifies existing or imminent weather hazards to aircraft in ight and creates warnings for transmission to the aviation community It also produces operational forecasts of weather conditions expected during the next 2 days that will affect domestic and international aviation interests As a Meteorological Watch Of ce MWO under regulations of the International Civil Aviation Organization ICAO meteorologists in this unit prepare and issue aviation area forecasts FAs and in ight weather advisories Airman s Meteorological Information AIRMET Significant Meteorological Information SIGMET and Convective SIGMETs for the contiguous 48 states Tropical Prediction Center TPC The Tropical Prediction Center TPC is located in Miami Florida The National Hurricane Center as an integral part of TPC issues hurricane advisories for the Atlantic the Caribbean the Gulf of Mexico the eastern Pacific and adjacent land areas The center also develops hurricane forecasting techniques and conducts hurricane research The Central Paci c Hurricane Center in Honolulu Hawaii issues advisories for the central Paci c Ocean TPC prepares and distributes tropical weather aviation and marine analyses forecasts and warnings As an MWO TPC meteorologists prepare and issue aviation forecasts SIGMETs and Convective SIGMETs for their tropical Flight Information Region FIR Weather Forecast Of ce WFO A Weather Forecast Office WFO issues various public and aviation forecast and weather warnings for its area of responsibility In support of aviation WFOs issue terminal aviation forecasts TAFs and transcribed weather broadcasts TWEBs As MWOs the Guam and Honolulu Hawaii WFOs issue aviation area forecasts and inflight advisories AIRMETs and international SIGMETs Figures 41 through 44 show locations for which TAFs are issued Figure 48 shows the TWEB routes 12 December 1999 Alaskan Aviation Weather Advisory Unit AAW U The Alaskan Aviation Weather Unit AAWU is a regional aviation forecast unit located in Anchorage Alaska As an MWO AAWU meteorologists prepare and issue International SIGMETs within the Alaskan FIR as well as domestic FAs and AIRMETs for Alaska and the adjacent coastal waters The AAWU prepares and disseminates to the FAA and the Internet a suite of graphic products including a graphic FA and a 24 and 36hour forecast of significant weather The AAWU is one of nine VAACs worldwide preparing Volcanic Ash Advisory Statements VAAS for the Anchorage FIR FEDERAL AVIATION ADMINISTRATION gFAAL The Federal Aviation Administration FAA is a part of the Department of Transportation The FAA provides a wide range of services to the aviation community The following is a description of those FAA facilities which are involved with aviation weather and pilot services FLIGHT SERVICE STATIONS FSSs The FAA is in the process of modernizing its Flight Service Station FSS program The older manual or nonautomated FSS is being consolidated into the newer automated FSS AF SS With about one per state and with lines of communications radiating out from it these new AF SSs are referred to as hub facilities Pilot services provided previously by the older FSSs have been consolidated into facilities with new technology to improve pilot weather brie ng services The FSS or AF SS provides more aviation weather brie ng service than any other US Government service outlet The FSS or AF SS provides pre ight and inflight brie ngs transcribed weather brie ngs scheduled and unscheduled weather broadcasts and furnishes weather support to ights in its area As a starting point for a pre ight weather brie ng a pilot may wish to listen to one of the recorded weather brie ngs provided by an FSS or AF SS For a more detailed brie ng pilots can contact the FSS or AF SS directly Transcribed Weather Broadcast TWEB The transcribed weather broadcast TWEB provides quot quot 39 and 39 39 39 information on lowmedium frequency LMF and very high frequency VHF omnidirectional radio range VOR facilities At TWEB equipment locations controlling two or more VORs the one used least for groundtoair communications preferably the nearest VOR may be used as a TWEB outlet simultaneously with the nondirectional radio beacon NDB facility December 1999 The sequence source and content of transcribed broadcast material shall be Vieri 0quot gt1 0 D IO Introduction Synopsis Prepared by selected WFOs and stored in Weather Message Switching Center WMSC Adverse Conditions Extracted from inflight weather advisories center weather advisories CWAs and alert severe weather watch bulletins AWWs TWEB Route Forecasts Includes the valid time of forecasts prepared by WFOs and stored in the WMSC Winds Aloft Forecast Broadcast for the location nearest to the TWEB The broadcast should include the levels for 3000 to 12000 feet but shall always include at least two forecast levels above the surface Radar Reports Local or pertinent radar weather reports SDs are used If there is access to realtime weather radar equipment the observed data is summarized using the SDs to determine precipitation type intensity movement and height Surface Weather Reports METARs Surfacespecial weather reports are recorded beginning with the local reports then the remainder of the reports beginning with the rst station east of true north and continuing clockwise around the TWEB location Density Altitude Includes temperature and the check density altitude statement for any station with a eld elevation at or above 2000 feet MSL and meets a certain temperature criteria Pilot Weather Reports PIREPs PIREPs are summarized If the weather conditions meet soliciting requirements a request for PIREPs will be appended Alert Notices ALNOT if applicable Closing Statement Items 2 3 4 and 5 are forecasts and advisories prepared by the NWS and are discussed in detail in Section 4 The synopsis and route forecasts are prepared speci cally for the TWEB by WFOs Adverse conditions outlooks and windstemperature aloft are adapted from in ight advisories area forecasts and the windstemperature aloft forecasts Radar reports and pilot reports are discussed in Section 3 Surface reports are discussed in Section 2 December 1999 Pilots Automatic Telephone Weather Answering System PATWAS Pilots automatic telephone weather answering system PATWAS provides a continuous telephone recording of meteorological information At PATWAS facilities where the telephone is connected to the TWEB the information contained in the broadcast shall be in accordance with the TWEB format PATWAS messages are recorded and updated at a minimum of every 5 hours beginning at 0600 and ending at 2200 local time using the following procedures 1 Introduction describing PATWAS area 2 Adverse Conditions Summarized in ight weather advisories center weather advisories alert severe weather watch bulletins and any other available information that may adversely affect ight in the PATWAS area 3 VFR Flight Not Recommended Statement VNR When current or forecast conditions surface based or aloft would make visual ight doubtful 4 Synopsis Should be a re ection of current and forecast conditions using synopsis products prepared by selected WFOs or extracted from the synopsis section of the area forecast Current Conditions Summarized current weather conditions over the broadcast area Surface Winds Provided from local reports Forecast Summarized forecast conditions over the PATWAS area Winds Aloft Summarized winds aloft as forecast for the local station or as interpolated from forecasts of adjacent stations for levels 3000 through 9000 feet or a minimum of at least two forecast levels above the highest terrain 9 Request for PIREPs if applicable Alert Notices ALNOT if applicable Closing Announcement 9 99 D IO The PATWAS service holds high operational priority This ensures the information is current and accurate If service is reduced during the period of 22000600 local time a suspension announcement is recorded including a time when the broadcast will be resumed The Airport Facili Directory lists PATWAS telephone numbers for FSS briefing of ces Telephone Information Brie ng Service TIBS Telephone information briefing service TIBS is provided by AF SSs and provides continuous telephone of 39 39 39 andor 39 information TIBS shall contain area andor route brie ngs airspace procedures and special announcements if applicable TIBS should also contain but not limited to METARs aviation terminal forecasts TAFs and winds temperatures aloft forecasts Each AF SS shall provide at least four route andor area brie ngs Area briefings should encompass a 50 NM radius Each briefing should require the pilot to access no more than two channels which shall be route andor areaspecific Pilots shall have access to NOTAM data through an area or route briefing on a separate channel designated speci cally for NOTAMs or by access to a briefer TIBS service is provided 24 hours a day Recorded information shall be updated as conditions change Area and route forecast channels shall be updated whenever material is updated December 1999 The order and content of the TIBS recording is as follows N Introduction Includes the preparation time and the route and or the area of coverage Adverse Conditions A summary of in ight weather advisories center weather advisories alert severe weather watch bulletins and any other available information that may adversely affect ight in the routearea 3 VFR Not Recommended Statement VNR Included when current or forecast conditions surface or aloft would make the ight under visual ight rules doubtful 4 Synopsis A brief statement describing the type location and movement of weather systems and or masses which might affect the route or the area 5 Current Conditions A summary of current weather conditions over the route area 6 Density Altitude A check density altitude statement will be included for any weather reporting point with a eld elevation at or above 2000 feet MSL and meets certain temperature criteria 7 En Route Forecast A summary of appropriate forecast data in logical order ie climb out en route and descent 8 Winds Aloft A summary of winds aloft forecast for the routearea for levels through 12000 feet 9 Request for PIREPs if applicable NOTAM information that affects the route area as stated above Military Training Activity Included in the closing announcement ALNOT Alert Announcement If applicable Closing Announcement Shall be appropriate for the facility equipment and the mode of operation D ID ID ID I WNb O Service may be reduced during the hours of 2200 and 0600 local time During the period of reduced service an announcement must be recorded The Airport Facility Directog lists TIBS telephone numbers for AF SS briefing offices A touchtone telephone is necessary to access the TIBS program For those pilots already in ight and needing weather information and assistance the following services are provided by ight service stations They can be accessed over the proper radio frequencies printed in ight information publications Hazardous In ight Weather Advisory Service IHWAS The hazardous in ight weather advisory service IHWAS is a continuous broadcast of in ight weather advisories ie SIGMETs Convective SIGMETs AIRMETs AWWs CWAs and urgent PIREPs The HIWAS broadcast area is de ned as the area within 150 NM of HIWAS outlets HIWAS broadcasts shall not be interrupted delayed except for emergency situations The service shall be provided 24 hours a day An announcement shall be made if there are no hazardous weather advisories Hazardous weather information shall be recorded if it is occurring within the HIWAS broadcast area The broadcast shall include the following elements 1 A statement of introduction including the appropriate areas and a recording time 2 A summary of in ight weather advisories center weather advisories and alert severe weather watch bulletins and any other weather not included in a current hazardous weather advisory 3 A request for PIREPs if applicable A recommendation to contact AF SSFSSFLIGHT WATCH for additional details concerning hazardous weather 5 December 1999 Once the HIWAS broadcast is updated an announcement will be made once on all communicationsNAVAID frequencies except emergency and En Route Flight Advisory Service EFAS In the event that a HIWAS broadcast area is out of service an announcement shall be made on all communicationsNAVAID frequencies except emergency and EFAS En Route Flight Advisory Service EFAS The en route ight advisory service EFAS or Flight Watch is a service from selected FSSs or AF SSs on a common frequency 1220 mHz below ight level FL 180 and on assigned discrete frequencies to aircraft at FL180 and above The purpose of EFAS is to provide en route aircraft with timely and pertinent weather data tailored to a specific altitude and route using the most current available sources of aviation meteorological information Additionally EFAS is a focal point for rapid receipt and dissemination of pilot reports Figure ll indicates the sites where EFAS and associated outlets are located To use this service call for ight watch Example Oakland FLIGHT WATCH TIHS IS The following paragraphs describe other FAA facilities which provide support to the aviation community Air Traffic Control System Command Center ATCSCC The Air Traf c Control System Command Center ATCSCC also known as central ow control is located in Hemdon Virginia ATCSCC has the mission of balancing air traffic demand with system capacity This ensures maximum safety and ef ciency for the National Airspace System while minimizing delays The ATCSCC utilizes the Traffic Management System aircraft situation display monitor alert the followon functions and direct contact with the air route traffic control center ARTCC and terminal radar approach control facility TRACON traf c management units to manage ow on a national as well as local level Because weather is the most common reason for air traf c delays and reroutings the ATCSCC is supported fulltime by Air Traf c Control System Command Center Weather Unit Specialists ATCSCCWUS These specialists are l quot 39 for the quot 39 quot of 39 39 39 information as it pertains to national air traf c ow management Air Route Traffic Control Center ARTCC An air route traffic control center ARTCC is a facility established to provide air traf c control service to aircraft operating on IFR ight plans within controlled airspace and principally during the en route phase of ight When equipment capabilities and controller workload permit certain advisory assistance services may be provided to VFR aircraft En route controllers become familiar with pertinent weather information and stay aware of current weather information needed to perform air traf c control duties En route controllers shall advise pilots of hazardous weather that may impact operations within 150 NM of the controller s assigned sector or area of jurisdiction Center Weather Service Unit CWSU The purpose of the center weather service unit CWSU is to provide weather consultation forecasts and advice to managers and staff within ARTCCs and to other supported FAA facilities The CWSU is a joint agency aviation weather support team located at each ARTCC The unit is composed of NWS meteorologists and FAA traffic management personnel the latter being assigned as Weather 17 December 1999 Coordinators The CWSU meteorologist provides FAA traf c managers with accurate and timely weather information This information is based on monitoring analysis and interpretation of realtime weather data at the ARTCC through the use of all available data sources including radar satellite PIREPs and various NWS products such as TAFs and area forecasts in ight advisories etc The ow or exchange of weather information between the CWSU meteorologists and the FAA personnel in the ARTCC is the responsibility of the Weather Coordinator Air Traffic Control Tower ATCT An air traffic control tower ATCT is a terminal facility that uses air ground communications visual signaling and other devices to provide ATC services to aircraft operating in the vicinity of an airport or on the movement area It authorizes aircraft to land or take off at the airport controlled by the tower or to transit the Class D airspace area regardless of ight plan or weather conditions IFR or VFR A tower may also provide approach control services Terminal controllers become familiar with pertinent weather information and stay aware of current weather information needed to perform air traf c control duties Terminal controllers shall advise pilots of hazardous weather that may impact operations within 150 NM of the controller s assigned sector or area of jurisdiction Tower cab and approach control facilities may opt to broadcast hazardous weather information alerts only when any part of the area described is within 50 NM of the airspace under the ATCT s jurisdiction The responsibility for disseminating weather information is shared with the NWS at many ATCT facilities Ifthe responsibility is not shared the controllers are properly certi ed and acting as official weather observers for the elements being reported An automatic terminal information service ATIS is a continuous broadcast of recorded information in selected terminal areas Its purpose is to improve controller effectiveness and to relieve frequency congestion by automating the repetitive transmission of noncontrol airportterminal area and meteorological information Direct User Access Terminal Service DUATS The direct user access terminal system DUATS provides current FAA weather and ight plan ling services to US Coast Guard and certified civil pilots The computerbased system receives and stores uptodate weather and NOTAM data from the FAA s WMSC Pilots using a personal computer modem and a telephone line can access the system and request specific types of weather briefings and other pertinent data for planned ights The pilot can also file amend or cancel ight plans while dialed into the system Further information about DUATS can be obtained from any AF SS or FAA Flight Standards District Of ce FSDO OBSERVATIONS Weather observations are measurements and estimates of existing weather conditions both at the surface and aloft When recorded and transmitted an observation becomes a report and reports are the basis of all weather analyses forecasts advisories and brie ngs The following paragraphs brie y describe the observation programs of the NWS and the FAA More detailed information on each program follows December 1999 SURFACE AVIATION WEATHER OBSERVATIONS METARs Surface aviation weather observations METARs include weather elements pertinent to ying A network of airport stations provides routine uptodate surface weather information For more information on surface aviation observation see Section 2 UPPER AIR OBSERVATIONS Upperair weather data is received from sounding balloons known as radiosonde observations and pilot weather reports PIREPs Upperair observations are taken twice daily at specified stations These upperair observations furnish temperature humidity pressure and wind data often to heights above 100000 feet In addition pilots are a vital source of upperair weather observations In fact aircraft in ight are the only means of directly observing turbulence icing and height of cloud tops For more information on PIREPs see Section 3 Recently some US and other intemational airlines have equipped their aircraft with instruments that automatically send weather observations via a satellite downlink These are important observations which are used by NCEP in their production of forecasts RADAR OBSERVATIONS The weather radar provides detailed information about precipitation winds and weather systems Doppler technology allows the radar to provide measurements of winds through a large vertical depth of the atmosphere even within clear air This information helps support public and aviation warning and forecast programs Figure 72 shows the weather radar network across the United States FAA terminal doppler weather radars TDWRs are being installed near a number of major airports around the country The TDWRs will be used to alert and warn airport controllers of approaching wind shear gust fronts and heavy precipitation which could cause hazardous conditions for landing or departing aircraft Also installed at major airports are the FAA airport surveillance radars With this radar speci c locations of six different precipitation intensity levels are available for the routing of air traf c in and about a terminal location However the radar s primary function is for aircraft detection LOW LEVEL WIND SHEAR ALERT SYSTEM LLWAS The lowlevel wind shear alert system LLWAS provides pilots and controllers with information on hazardous surface wind conditions on or near the airport that create unsafe landing or departure conditions LLWAS evaluates wind speed and direction from sensors on the airport periphery with center eld wind data During the time that an alert is posted air traffic controllers provide wind shear advisories to all arriving and departing aircraft SATELLITE IMAGERY Visible infrared IR and other types of images or pictures of clouds are taken from weather satellites in orbit These images are then made available on a nearrealtime basis to NWS and FAA facilities Satellite pictures are an important source of weather information For more information on satellite products see Section 3 December 1999 COMMUNICATION SYSTEM High speed communications and automated data processing have improved the ow of weather data and products through the nation s weather network The ow of weather information within and between agencies is becoming faster as computers and satellites are being used to facilitate the exchange of data A new computerbased advanced weather interactive processing system AWIPS workstation is being deployed for the NWS This system is replacing the current system and will allow quicker dissemination of weather information AWIPS will be linked with the weather radars to provide better detection observing and forecasting of weather systems especially severe weather The ow of alphanumeric weather information to the FAA service outlets is accomplished through leased lines to computerbased equipment The NWS and FAA service outlets exchange weather information through the use of graphic products and alphanumeric information Graphic products weather maps are received by FAA service outlets from NCEP through a private sector contractor Alphanumeric information exchanged through telecommunication gateways at NWS and FAA switching centers serves to pass data between the various FAA facilities NWS and other users USERS The ultimate users of the aviation weather service are pilots and dispatchers Maintenance personnel may use the service to keep informed of weather that could cause possible damage to unprotected aircraft Pilots contribute to as well as use the service Pilots should send PIREPs to help fellow pilots briefers and forecasters The service can be no better or more complete than the information that goes into it In the interest of safety and in compliance with Title 14 Code of Federal Regulations all pilots should get a complete weather briefing before each ight It is the responsibility of the pilot to ensure heshe has all the information needed to make a safe ight OBTAINING A GOOD WEATHER BRIEFING When requesting a brie ng pilots should identify themselves as pilots and give clear and concise facts about their ight Type of ight VFR or IFR Aircraft identi cation or pilot s name Aircraft type Departure point Proposed time of departure Flight altitudes Route of ight Destination Estimated time en route ETE SOQONOF IerNT December 1999 With this background the briefer can proceed directly with the briefing and concentrate on weather relevant to the ight The weather information received depends on the type of brie ng requested A standard briefing should include 1 Adverse conditions 39 39 or quot 39 439 reported or forecast that may in uence a pilot to alter the proposed ight 2 VFR ight not recommended VNR VFR ight is proposed and sky conditions or visibilities are present or forecast surface or aloft that in the judgment of the AF SSF SS briefer would make ight under visual ight rules doubtful 3 Synopsis A brief statement describing the type location and movement of weather systems and or air masses which might affect the proposed ight 4 Current conditions A summary from all available sources reporting weather conditions applicable to the ight 5 En Route forecast A summary from appropriate data forecast conditions applicable to the proposed ight 6 Destination forecast Destination forecast including signi cant changes expected within 1 hour before and after the ETA 7 Winds aloft Forecast winds aloft for the proposed route temperature information on request 8 NOTAMs Provides NOTAMs pertinent to the ight ATC delays Informs the pilot of any known ATC delays andor ow control advisories that may affect the proposed ight Request for PIREPs A request is made if a report of actual in ight conditions would be bene cial or when conditions meet the criteria for solicitation of PIREPs EFAS Informs pilots of the availability of Flight Watch for weather updates Any other information the pilot requests e g military training routes etc 0 O ND I An abbreviated briefing will be provided at the user s request 1 To supplement mass disseminated data 2 To update a previous brie ng 3 To request that the briefing be limited to speci c information An outlook brie ng will be provided when the proposed departure is 6 hours or more from the time of the briefing Brie ng will be limited to applicable forecast data needed for the proposed ight The FSSAFSS s purpose is to serve the aviation community Pilots should not hesitate to ask questions and discuss factors they do not fully understand The briefing should be considered complete only when the pilot has a clear picture of what weather to expect It is also advantageous for the pilot to make a nal weather check immediately before departure if at all possible ZI39I mg L P SPF II mm mquot m Saw NOT an now our ms m m L um DIK m 0L MOT E an m M NEO Tm m M 2 us LKV GNG quotw m as r m m an cm HR um quotYA NON A B LSK m1 KG DET W 0 am on cm H m m HMO w m m OXI ClE NE 03quot Tquot ILC m 888 s Mic OAK FAT GR OMA D 392 3m 0 IND m 58 EN 6 m c c CHI anquot wquot 35 GJTASE k C quotU BP an aquot m i V 362 H VI m m LYquot w N 456 NW GU V8 MA m H I 0 P94 WT as u ONA Mm HHR GAG m wquot OKC u JLI m II w w CE 1 IISL m an GWO Tcs 393 nun L BSA ADI C 5quot NON quotV0 Esp m GDP w m u we PST m ms cxo LON O LEGEND Iou LS Equot W FLIGHT WATCH CONTROL w STATIONS FWCS 0 COMMUNICATIONS OUTLETS quot390 m 0 I Figure 1 1 EFAS Sites and Communication Outlets m 6661 laqwaoaq December 1999 Section 2 AVIATION ROUTINE WEATHER REPORT METAR The aviation routine weather report METAR is the weather observer s interpretation of the weather conditions at a given site and time The METAR is used by the aviation community and the National Weather Service NWS to determine the ying category visual fight rules VFR marginal VFR MVFR or instrument ight rules IFR of the airport as well as produce the Aviation Terminal Forecast TAF See Section 4 Although the METAR code is being adopted worldwide each country is allowed to make modifications or exceptions to the code for use in that particular country The USA reports temperature and dew point in degrees Celsius and continues to use current units of measurement for the remainder of the report The elements in the body of a METAR report are separated with a space The only exception is temperature and dew point that are separated with a solidus I When an element does not occur or cannot be observed the preceding space and that element are omitted from that particular report A METAR report contains the following elements in order as presented Type of report ICAO station identi er Date and time of report Modi er as required Wind Visibility Runway visual range RVR as required Weather phenomena Sky condition Temperaturedew point group Altimeter 12 Remarks RMK as required Sapwssmwpwnzve The following paragraphs describe the elements in a METAR report A sample report will accompany each element with the subject element highlighted TYPE OF REPORT METAR KLAX 140651Z AUTO 00000KT 1SM R35L4500V6000FT RA BR BKN030 1010 A2990 RMK A02 There are two types of reports The METAR and the aviation selected special weather report SPECI The METAR is observed hourly between 45 minutes after the hour till the hour and transmitted between 50 minutes after the hour till the hour It will be encoded as a METAR even if it meets SPECI criteria The SPECI is a nonroutine aviation weather report taken when any of the SPECI criteria have been observed The criteria are listed in Table 21 SPECI Criteria December 1999 Table 2 1 SPECI Criteria Report Element Criteria Wind Wind direction changes by 45 degrees or more in less than 15 minutes and the wind speed is 10 knots or more throughout the windshift Visibility Surface visibility as reported in the body of the report decreases to less than or if below increases to equal or exceeds 32 or 1mile or the lowest standard instrument approach procedure minimum as published in the National Ocean Service US Instrument Procedures If none is published use 1z mile RVR Changes to above or below 2400 feet Tornado Funnel Cloud Waterspout When observed or when disappears from sight ends Thunderstorm Begins or ends Precipitation When freezing precipitation or ice pellets begin end or change intensity or hail begins or ends Squalls When they occur Ceilings The ceiling forms or dissipates below decreases to less than or if below increases to equal or exceeds 3000 1500 1000 or 500 feet or the lowest standard instrument approach procedure minimum as published in the National Ocean Service US Instrument Procedures If none is published use 200 feet Sky Condition A layer of clouds or obscuring phenomenon aloft that forms below 1000 feet Volcanic Eruption When an eruption is first noted Aircraft Mishap Upon notification of an aircraft mishap unless there has been an intervening observation Miscellaneous Any other meteorological situation designated by the agency or which in the opinion ofthe observer is critical ICAO STATION IDENTIFIER METAR KLAX 140651Z AUTO 00000KT ISM R35L4500V6000FT RA BR BKN030 1010 A2990 RMK A02 The METAR code uses International Civil Aviation Organization ICAO fourletter station identifiers that follow the type of report In the conterminous United States the threeletter identi er is prefixed with K For example SEA Seattle becomes KSEA Elsewhere the first one or two letters of the ICAO identi er indicate in which region of the world and country or state the station is located Paci c locations such as Alaska Hawaii and the Mariana Islands start with P followed by an A H or G respectively The last two letters re ect the speci c reporting station identi cation If the location s threeletter identi cation begins with an A H or G the P is added to the beginning If the location s threeletter identi cation does not begin with an A H or G the last letter is dropped and the P is added to the beginnmg December 1999 Examples ANC Anchorage AK becomes PANC 0ME Nome AK becomes PAOM HNL Honolulu HI becomes PHNL KOA Keahole Point HI becomes PHKO UAM Anderson AFB Guam becomes PGUA Canadian station identi ers start with C Example Toronto Canada is CYYZ Mexican and western Caribbean station identi ers start with M Examples Mexico City Mexico is MlVIMX Guantanamo Cuba is MUGT Santo Domingo Dominican Republic is MDGM Nassau Bahamas is The identi er for the eastern Caribbean is T followed by the individual country39s letter Example San Juan Puerto Rico is TJSJ For a complete worldwide listing see ICAO Document 7910 Location Indicators DATE AND TIME OF REPORT METAR KLAX 140651Z AUTO 00000KT 1SM R35L4500V6000FT RA BR BKN030 1010 A2990 RMK A02 The date and time the observation is taken are transmitted as a sixdigit datetime group appended with Z to denote Coordinated Universal Time UTC The rst two digits are the date followed with two digits for hour and two digits for minutes If a report is a correction to a previously disseminated erroneous report the time entered on the corrected report shall be the same time used in the report being corrected MODIFIER AS RES QUIREDg METAR KLAX 140651Z AUTO 00000KT ISM R35L4500V6000FT RA BR BKN030 1010 A2990 RMK A02 The modifier element if used follows the datetime element The modifier AUTO identi es a METARSPECI report as an automated weather report with no human intervention If AUTO is shown in the body of the report A01 or A02 will be encoded in the remarks section of the report to indicate the type of precipitation sensor used at the station A remark of A01 indicates a report from a station that does not have a precipitation discriminator and an A02 remark indicates a report from a station 23 December 1999 which has a precipitation discriminator The absence of AUTO indicates that the report was made manually or the automated report had human augmentationbackup The modifier COR identifies a corrected report that is sent out to replace an earlier report with an error Example METAR KLAX 140651Z COR WIND METAR KLAX 140651Z AUTO 00000KT ISM R35L4500V6000FT RA BR BKN030 1010 A2990 RMK A02 The wind element is reported as a vedigit group six digits if speed is over 99 knots The first three digits are the direction from which the wind is blowing in tens of degrees referenced to true north Directions less than 100 degrees are preceded with a zero The next two digits are the average speed in knots measured or estimated or if over 99 knots the next three digits Example 340105KT If the wind speed is less than 3 knots the wind is reported as calm 00000KT If the wind is gusty 10 knots or more between peaks and lulls G denoting gust is reported after the speed followed by the highest gust reported The abbreviation KT is appended to denote the use of knots for wind speed Other countries may use kilometers per hour or meters per second If the wind direction is variable by 60 degrees or more and the speed is greater than 6 knots a variable group consisting of the extremes of the wind directions separated by V will follow the wind group Example 08012G25KT 040V 120 The wind direction may also be considered variable if the wind speed is 6 knots or less and is varying in direction 60degree rule does not apply This is indicated with the contraction VRB Example VRB04KT WIND REMARKS At facilities that have a wind recorder or at automated weather reporting systems whenever the peak wind exceeds 25 knots PK WND will be included in the Remarks element in the next report The peak wind remark includes three digits for direction and two or three digits for speed followed by the time in hours and minutes of occurrence Ifthe hour can be inferred from the report time only the minutes are reported December 1999 Example PK WND 28045 15 When a windshift occurs WSHFT will be included in the Remarks element followed by the time the windshift began with only minutes reported if the hour can be inferred from the time of observation A windshift is indicated by a change in wind direction of 45 degrees or more in less than 15 minutes with sustained winds of 10 knots or more throughout the windshift The contraction FROPA may be entered following the time if the windshift is the result of a frontal passage Example WSHFT 30 FROPA VISIBILITY METAR KLAX 140651Z AUTO 00000KT ISM R35L4500V6000FT RA BR BKN030 1010 A2990 RMK A02 Prevailing visibility is reported in statute miles followed by a space fractions of statute miles as needed and the letters SM Other countries may use meters or kilometers Prevailing visibility is considered representative of the visibility conditions at the observing site Prevailing visibility is the greatest visibility equaled or exceeded throughout at least half the horizon circle which need not be continuous When visibilities are less than 7 miles the restriction to visibility will be shown in the weather element The only exception to this rule is that if volcanic ash low drifting dust sand or snow is observed it is reported even if it does not restrict visibility to less than 7 miles VISIBILITY REMARKS If tower or surface visibility is less than 4 statute miles the lesser of the two will be reported in the body of the report the greater will be reported in the Remarks element Example TWR VIS 1 12 or SFC VIS 1 12 Automated reporting stations will show visibility less than 14 statute mile as M14SM and visibility 10 or greater than 10 statute miles as 10SM For automated reporting stations having more than one visibility sensor sitespeci c visibility which is lower than the visibility shown in the body will be shown in the Remarks element Example VIS 2 12 RWY 11 When the prevailing visibility rapidly increases or decreases by 12 statute mile or more during the observation and the average prevailing visibility is less than 3 statute miles the visibility is variable Variable visibility is shown in the Remarks element with the minimum and maximum visibility values separated by a V December 1999 Example VIS 12V2 Sector visibility is shown in the Remarks element when it differs from the prevailing visibility and either the prevailing or sector visibility is less than 3 miles Example VIS NE 2 12 RUNWAY VISUAL RANGE RVR AS REQUIRED METAR KLAX 140651Z AUTO 00000KT ISM R35L4500V6000FT RA BR BKN030 1010 A2990 RMK A02 Runway visual range RVR follows the visibility element RVR when reported is in the following format R identi es the group followed by the runway heading and if needed the parallel runway designator next is a solidus I last is the visual range in feet meters in other countries indicated by FT RVR is shown in a METARSPECI if the airport has RVR equipment and whenever the prevailing visibility is l statute mile or less andor the RVR value is 6000 feet or less When the RVR varies by more than one reportable value the lowest and highest values are shown with V between them Example R3 5L4500V6000FT When the observed RVR is above the maximum value which can be determined by the system it should be reported as P6000 where 6000 is the maximum value for this system When the observed RVR is below the minimum value which can be determined by the system it should be reported as M0600 where 600 is the minimum value for this system Example R27P6000FT and R12CM0600FT WEATHER PHEN OMEN A METAR KLAX 140651Z AUTO 00000KT ISM R35L4500V6000FT RA BR BKN030 1010 A2990 RMK A02 Weather phenomena is broken into two categories qualifiers and weather phenomena December 1999 QUALIFIERS Intensity Intensity may be shown with most precipitation types A denotes a light intensity level no symbol denotes a moderate intensity level and a denotes a heavy intensity level When more than one type of precipitation is present the intensity refers to the rst precipitation type most predominant See Table 22 Example SHRASN indicates heavy rainshowers and snow Table 2 2 Intensity Quali ers Intensity Qu ali ers Light Moder ate Heavy Proximity Proximity is applied to and reported m for weather phenomena occurring in the vicinity of the airport Vicinity of the airport is de ned to be between 5 and 10 miles of the usual point of observation for obscuration and just beyond to point of observation to 10 miles for precipitation It is denoted by VC Intensity and VC will M be shown in the same group Examples VCSH indicates showers in the vicinity of the airport VCFG indicates fog in the vicinity of the airport Descriptor The eight descriptors shown in Table 23 further identify weather phenomena and are used with certain types of precipitation and obscurations Although TS and SH are used with precipitation and may be preceded with an intensity symbol the intensity still applies to the precipitation and not the descriptor Example TSRA is a thunderstorm with heavy rain and not a heavy thunderstorm with rain December 1999 Table 2 3 Descriptor Quali ers Descriptor MI1 Sh allow BCz Patches DR3 Low drifting BL Blowing SH Showers TS Thunderstorm FZ Freezing PR Partial 1MI shall be used only to further describe fog that has little vertical extent less than 6 feet 2BC shall be used only to further describe fog that has little vertical extent and reduces horizontal visibility 3DR shall be used when dust sand or snow is raised by the wind to less than 6 feet 4BL shall be used when dust sand snow andor spray is raised by the wind to a height of 6 feet or more WEATHER PHEN OMEN A If more than one significant weather phenomenon is observed entries will be listed in the following order Tornadic activity thunderstorms and weather phenomena in order of decreasing predominance ie the most dominant type is reported rst If more than one significant weather phenomenon is observed except precipitation separate weather groups will be shown in the report No more than three weather groups will be used to report weather phenomena at or in the vicinity of the station If more than one type of precipitation is observed the appropriate contractions are combined into a single group with the predominant type being reported rst In such a group any intensity will refer to the rst type of precipitation in the group Refer to Table 24 while reading the rest of this section Examples TSRA indicates thunderstorm with moderate rain SHRA indicates heavy rainshowers FZRA indicates light freezing rain Precipitation The types of precipitation in the METAR code are shown in Table 24 Precipitation is any form of water particle whether liquid or solid that falls from the atmosphere and reaches the ground December 1999 Examples GR is used to indicate hail 1 inch in diameter or larger GS is used to indicate hail less than 1 inch in diameter UP is unknown precipitation and is used only at automated sites This occurs when light precipitation is falling but the precipitation discriminator cannot determine the precipitation type This situation usually occurs when rain and snow are falling at the same time Obscurations The types of obscuration phenomena in the METAR code are shown in Table 24 They are any phenomena in the atmosphere other than precipitation that reduce horizontal Visibility Examples BR is used to indicate mist restricting Visibility and is used only when the Visibility is from 58 mile to 6 miles FG is used to indicate fog restricting Visibility and is used only when Visibility is less than 58 mile Other The other weather phenomena shown in the table are reported when they occur Examples SQ is a sudden increase in wind speed of at least 16 knots the speed rising to 22 knots or more and lasting at least 1 minute FC is used to denote a tornado or waterspout FC is used to denote a funnel cloud Table 2 4 Weather Phenomena P1 quot quot Obscuration Other DZ Drizzle BR Mist PO DustSand whirls RA Rain FG Fog SQ Squalls SN Snow DU Dust FC Funnel cloud SG Snow grains SA Sand FC Tornado or Waterspout IC Ice crystals HZ Haze SS Sandstorm PL Ice pellets PY Spray DS Dust storm GR Hail VA Volcanic ash GS Small hail or Snow pellets FU Smoke UP Unknown precipitation December 1999 Weather BeginsEnds When weather begins or ends the Remarks element will show the beginning and ending times of any type of precipitation or thunderstorms Types of precipitation may be combined if beginning or ending times are the same Example RAB05E30SNB30E45 This means that rain began at 5 minutes past the hour and ended at 30 minutes past the hour snow began at 30 minutes past the hour and ended at 45 minutes past the hour Example TSB05E45 This means a thunderstorm began at 5 minutes past the hour and ended at 45 minutes past the hour Hailstone Size When hailstones GR are shown in the body of a report the largest hailstone size is shown in the Remarks element in l4inch increments and identi ed with the contraction GR Hailstones less than 14 inch are shown in the body of a report as GS and no remarks are entered indicating hailstone size Example GR 1 3A 210 December 1999 SKY CONDITION METAR KLAX 140651Z AUTO 00000KT 1SM R35L4500V6000FT RA BR BKN030 1010 A2990 RMK AO2 Sky condition is reported in the following format AmountHeight Type as required or Inde nite CeilingHeight Vertical Visibility AMOUNT A clear sky a layer of clouds or an obscuring phenomenon is reported by one of the six sky cover contractions See Table 25 When more than one layer is reported they are reported in ascending order of height For each layer above a lower layer or layers the sky cover for that higher layer will be the total sky cover that includes that higher layer and all lower layers In other words the summation of the cloud layers from below and at that higher level determines what sky cover is reported This summation includes both clouds and obscuration The amount of sky cover is reported in eighths of the sky using the contractions in Table 25 Table 2 5 Reponable Contractions for Sky Cover Report able Meaning Summ ation Amount SKC will be reported at manual stations The abbreviation CLR shall be used at automated stations when no clouds below 12000 feet are detected Note For aviation purposes the ceiling is de ned as the height AGL of the lowest broken or overcast layer aloft or vertical visibility into an obscuration HEIGHT Cloud bases are reported with three digits in hundreds of feet above ground level Example SCT020 Clouds above 12000 feet cannot be detected by automated reporting systems At reporting stations located in the mountains if the cloud layer is below the station level the height of the layer will be shown as three solidi Example SCT 211 December 1999 18 5000 4000 3000 2000 10 0 HORIZO FACE quot EARTH Figure 21 Few sky cover at 2000 feet 28 and scattered sky cover at 4000 feet 4 8 The summation of sky cover would be coded as FEW020 SCT040 Figure 22 The sky cover consists of few clouds at 1000 feet 28 scattered clouds at 3000 feet 38 and broken clouds at 5000 feet 68 This is coded as FEW010 SCT030 BKN050 212 December 1999 TYPE AS REQUIRED If towering cumulus clouds TCU or cumulonimbus clouds CB are present they are reported after the height that represenm their base Example BKNOZSCB or SCT040TCU Figure 23 Towering Cumulus TCU The significance of this cloud is that it indicates the atmosphere in the lower altitudes is unstable and conducive to turbulence Photo courtesy of National Severe Storms LaboratoryUniversity of Oklahoma December 1999 Figure 24 Currrulonimbus CE The anvil portion of a CE is composed of ice crystals The CB or thunderstorm cloud contains most types of aviation weather hazards particularly turbulence icing hail and lowlevel wind shear LLWS Photo courtesy of Doug Streu INDEFINITE CEILINGHEIGHTS VERTICAL VISIBILITY The height into an inde nite ceiling is preceded with VV followed by three digits indicating the vertical visibility in hundreds of feet above ground level The layer is spoken as inde nite ceiling and indicates total obscuration Example VVOOZ Partial Obscurations The amount of obscuration is reported in the body of the METAR when the sky is partially obscured by a surfacebased phenomenon by indicating the amount of obscuration as FEW SCT or BIG J followed with three zeros 000 The type of obscuring phenomenon is stated in the Remarks element and precedes the amount of obscuration and three zeros For example if fog is hiding gtl8 to 28 of the sky it will be coded in the body of the METAR as FEWOOO Because the fog is partially obscuring the sky a remark is required See Figure 25 Example of Remark FG FEWOOO December 1999 Cloud n lowe Figure 25 The sky cover consists of surfacebased obscuration and an overcast layer at 3000 feet This is coded as SCT000 OVC030 with FG SCT000 in remarks The sky cover and ceiling as determined from the ground represent as nearly as possible what the pilot should experience in ight In other words a pilot ying at or above a reported ceiling layer BKN OVC should see less than half the surface below A pilot descending through a surfacebased total obscuration should rst see the ground directly below from the height reported as vertical visibility into the obscuration However due to the differing viewing points of the pilot and the observer the observed values and what the pilot sees do not always exactly agree Figure 26 illustrates the effect of an obscured sky on the vision from a descending aircraft 215 December 1999 3 MISSED APPROACH h SLANT RANGE VISIBILITY REPORTED VERTICAL VISIBILITY SLANT RANGE gag VISIBILITY RUNWAY Figure 26 The obscuration limits runway acquisition due to slant range effects A This pilot would be able to see the ground but not the runway The pilot will not be able to see the runway until position B which is at a much lower altitude prosition A represented approach minimums the approach could not be continued and a missed approach must be executed ADDITIONAL SKY CONDITION REMARKS Whenever the ceiling is below 3000 feet and is variable the remark CIG will be shown in the Remarks element followed with the lowest and highest ceiling heights separated with a V Example CIG 005V010 When an automated station uses 39 39 39 quot quot quot sensors it I if sky conditions that differ from the ceiling height in the body of t e report will be shown in the Remarks element Example CIG 002 RWY 11 When a layer is varying in sky cover the variability range will be shown in the Remarks element If there is more than one cloud layer of the same coverage the variable layer will be identi ed by including the layer height Example BKN014 V OVC When signi cant clouds are observed they are shown in the Remarks element The following cloud types are shown 216 December 1999 Towering cumulus TCU and direction from the station Example TCU 39 R39 u 39 RMAM direuiun 39 and direction of movement if known Ifthe clouds are beyond 10 miles from the airport DSNT will indicate that they are distant See Figure 27 Examples CB DSNT E or CBMAM E MOV NE For TCU and CB see Figures 23 and 24 Figure 27 Cumulonimbus Mammatus CBMAM This characteristic cloud can result from Violent am quot L 39 39 39 ate Lul uuience of up and downdr gr Photo courtesy Grant Goodge taken at Asheville NC on 41587 December 1999 Altocumulus castellanus ACC standing lenticular stratocumulus SCSL altocumulus ACSL or cirrocumulus CCSL or rotor clouds ROTOR CLD will show a remark describing the clouds if needed and the direction from the station Examples ACC NW or ACSL SW Figure 28 for ACC see Figure 29 for standing lenticular clouds Figure 28 Altocumulus Castellanus ACC ACC indicates unstable conditions aloft but not necessarily below the base of the cloud Photo courtesy of National Severe Storms LaboratoryUniversity of Oklahoma December 1999 Fhrm 70 lamIHmyT o I TL The L M Y CCSL A m Goodge taken at Concord CA in 1970 TEMPERATUREDEW POINT GROUP M39FTAR KI A A T VT ISM RA BR BKN030 1010 A2990 RMKACl W mi mm 39 N 39 quot m muquot omitted from the report ALTIMIETER M39FTAR KT A A W VT ISM RA BR BKN030 1010 A2990 RMZKACz METAR or SPECIreport 39 quot 39 mm c quotm w L 4 4L A n m 1 December 1999 ALTIMETER REMARKS When the pressure is rising or falling rapidly at the time of observation Remarks element will show PRESRR or PRESFR respectively Some stations also include the sealevel pressure which is different from altimeter It is shown in the Remarks element as SLP being the remark identifier followed by the sealevel pressure in hectopascals hPa a unit of measurement equivalent to millibar mb Example SLP982 REMARKS gRMK gAS REQUIRED METAR KLAX 140651Z AUTO 00000KT ISM R35L4500V6000FT RA BR BKN030 1010 A2990 RMK A02 Remarks will be included in all observations when appropriate in the order as presented in Table 26 The contraction RMK follows the altimeter in the body and precedes the actual remarks Time entries will be shown as minutes past the hour if the time reported occurs during the same hour the observation is taken Ifthe hour is different hours and minutes will be shown Location of phenomena within 5 statute miles of the point of observation will be reported as at the station Phenomena between 5 and 10 statute miles will be reported as in the vicinity VC Phenomena beyond 10 statute miles will be shown as distant DSNT Direction of phenomena will be indicated with the eight points of the compass ie N NE E SE S SW W NW Distance remarks are in statute miles except for automated lightning remarks that are in nautical miles Movement of clouds or weather will be indicated by the direction toward which the phenomenon is moving There are two categories of remarks automated manual and plain language and additive and automated maintenance data AUTOMATED MANUAL AND PLAIN LANGUAGE REMARKS CATEGORY This group of remarks may be generated from either manual or automated weather reporting stations and generally elaborate on parameters reported in the body of the report See Table 26 December 1999 Table 2 6 Automated Manual and Plain Language Remarks 1 Volcanic Eruptions MT AUGUSTINE VOLCANO 70 MILES SW ERUPTED 231505 LARGE ASH CLOUD EXTENDING TO APRX 221 December 1999 FIGURE 210 Virga Virga is precipitation falling from a cloud but evaporating before reaching the ground Virga results when air below the cloud is very dry and is common in the western part of the country Virga associated with showers suggests strong downdra s with possible moderate or greater turbulence Photo courtesy of Grant Goodge ADDITIVE AND AUTOMATED MAINTENANCE DATA REMARKS CATEGORY Additive data groups are reported only at designated stations The maintenance data groups are reported only from automated weather reporting stations The additive data and maintenance groups are not used by the aviation community 222 December 1999 EXAMPLES OF METAR REPORTS AND EXPLANATION S METAR KMKL 021250Z 33018KT 290V360 12SM R312600FT SN BLSN FG VV008 00M03 A2991 RMK RAESNB42 SLPNO T00111032 12SM R312600FT SN BLSN FG VV008 00M03 A2991 RMK RAESN B42 SLPNO T00111032 aviation routine weather report Jackson TN date 02 time 1250 UTC wind 330 at 18 knots wind direction variable between 290 and 360 degrees visibility onehalf statute mile runway 31 RVR 2600 moderate snow blowing snow and fog inde nite ceiling 800 temperature 0 C dew point 3 C altimeter 2991 remarks rain ended at four two snow began at four two sealevel pressure not available temperature 110 C dew point 32 C The following is an example of the phraseology used to relay this report to a pilot Optional phrases or words are shown in parentheses Jackson Tennessee one two ve zero observation wind three three zero at one eight wind variable between two niner zero and three six zero visibility onehalf runway three one RVR two thousand six hundred heavy snow blowing snow fog indefinite ceiling eight hundred temperature zero dew point minus three altimeter two niner niner one December 1999 METAR KSFO 031453Z VRB02KT 7SM MIFG SKC 1514 A3012 RMK SLP993 6 T01500139 56012 METAR aviation routine weather report KSFO San Francisco CA 031453Z date 03 time 1453 UTC VRB02KT wind variable at 2 knots 7SM visibility 7 statute miles MIFG shallow fog SKC clear 1514 temperature 15 C dew point 14 C A3012 altimeter 3012 RMK remarks SLP993 sealevel pressure 9993 hectopascals 6 an indeterminable amount of precipitation has occurred over the last 3 hours T01500139 temperature 150 o C dew point 1390 C 56012 atmospheric pressure lower since previous 3 hours ago The following is an example of the phraseology used to relay this report to a pilot Optional phrases or words are shown in parentheses San Francisco one four ve three observation wind variable at two visibility seven shallow fog clear temperature one ve dew point one four altimeter three zero one two SPECI KCVG 312228Z 28024G36KT 34SM TSRA SQ BKN008 OVC020CB 2823 A3000 RMK TSB24 TS OHD MOV E SPECI aviation selected special weather report KCVG Covington KY 312228Z date 31 time 2228 UTC 28024G36KT wind 280 at 24 gusts 36 knots 34SM visibility threequarters statute mile TSRA SQ thunderstorm with heavy rain and squalls BKN008 OVC020CB ceiling 800 broken 2000 overcast cumulonimbus 2823 temperature 28 C dew point 23 C A3000 altimeter 3000 RMK remarks TSB24 thunderstorm began at two four TS OHD MOV E thunderstorm overhead moving east The following is an example of the phraseology used to relay this report to a pilot Optional phrases or words are shown in parentheses Covington Kentucky special report two eight observation wind two eight zero at two four gusts three six visibility threequarters thunderstorm heavy rain squall ceiling eight hundred broken two thousand overcast cumulonimbus temperature two eight dew point two three altimeter three zero zero zero thunderstorm began two four thunderstorm overhead moving east More examples without phraseology December 1999 METAR KLAX 140651Z AUTO 00000KT 10SM RA SCT080 1205 A2990 RMK A02 METAR aviation routine weather report KLAX Los Angeles CA 140651Z date 14 time 0651 UTC AUTO automated site 00000KT calm winds 10SM visibility 10 statute miles RA light rain SCT080 8000 scattered 1205 temperature 12 C dew point 5 C A2990 altimeter 2990 RMK remarks A02 automated observation with precipitation discriminator SPECI KDEN 241310Z 09014G35KT 14SM SN FG VV002 0101 A2975 RMK A02 TWR VIS 12 RAE08SNB08 SPECI aviation selected special weather report KDEN Denver CO 241310Z date 24 time 1310 UTC 09014G35KT wind 090 at 14 gusts to 35 knots 14SM visibility onequarter statute mile SN FG heavy snow and fog VV002 inde nite ceiling 200 0101 temperature 1 C dew point 1 C A2975 altimeter 2975 RMK remarks A02 automated observation with precipitation discriminator TWR VIS 12 tower visibility onehalf RAE08SNB08 rain ended and snow began at 08 minutes after the hour December 1999 METAR KSPS 301656Z 06014KT 020V090 3SM TSRA FEW040 BKN060CB 12 A2982 RMK OCNL LTGICCG NE TSB17 TS E MOV NE PRESRR SLP093 METAR KSPS 301656Z 06014KT 020V090 3SM TSRA FEW040 BKN060CB 12 A2982 RMK OCNL LTGICCG NE TSB17 TS E MOV NE PRESRR SLP093 aviation routine weather report Wichita Falls TX date 30 time 1656 UTC wind 060 at 14 knots varying between 020 and 090 degrees visibility 3 statute miles thunderstorm with light rain few clouds at 4000 ceiling 6000 broken cumulonimbus temperature 12 C dew point is missing altimeter 2982 remarks occasional lightning in cloud cloudtoground northeast thunderstorm began 17 thunderstorm east moving northeast pressure rising rapidly sealevel pressure 10093 hectopascals SPECI KBOS 051237Z VRB02KT 34SM R15R4000FT BR OVC004 0505 A2998 RMK A02 CIG 002V006 SPECI KBOS 051237Z VRB02KT 34SM R15R4000FT CIG 002V006 aviation selected special weather report Boston MA date 5 time 1237 UTC variable wind at 2 knots visibility threequarters statute mile runway visual range on runway 15R 4000 feet mist ceiling 400 overcast temperature 5 C dew point 5 C altimeter 2998 remarks automated observation with precipitation discriminator ceiling variable 200 to 600 226 December 1999 Section 3 PILOT AND RADAR REPORTS SATELLITE PICTURES AND RADIOSONDE ADDITIONAL DATA RADATs The preceding section explained the decoding of METAR reports However these spot reports are only one facet of the total current weather picture Pilot and radar reports satellite pictures and radiosonde additional data RADATs help to ll the gaps between stations PILOT WEATHER REPORTS IREPs No observation is more timely than the one made from the ight deck In fact aircraft in ight are the m means of observing icing and turbulence Other pilots welcome pilot weather reports PIREPs as well as do the briefers and forecasters A PIREP always helps someone and becomes part of aviation weather Pilots should report any observation that may be of concern to other pilots Also if conditions were forecasted but were not encountered a pilot should also provide a PIREP This will help the NWS to verify forecast products and create accurate products for the aviation community Pilots should help themselves the aviation public and the aviation weather forecasters by providing PIREPs A PIREP is transmitted in a prescribed format see Table 31 Required elements for all PIREPs are type of report location time ight level aircraft type and at least one weather element encountered When not required elements without reported data are omitted All altitude references are mean sea level MSL unless otherwise noted Distance for visibility is in statute miles and all other distances are in nautical miles Time is in universal coordinated time UTC Table 3 1 PIREP Format December 1999 Table 3 2 Encoding PIREPs UUAUA Type of report URGENT UUA Any PIREP that contains any ofthe following weather phenomena tornadoes funnel clouds or waterspouts severe or extreme turbulence including clear air turbulence CAT severe icing hail volcanic ash low level wind shear LLWS pilot reports air speed fluctuations of 10 knots or more within 2000 feet ofthe surface any other weather phenomena reported which are considered by the controller to be hazardous or potentially hazardous to flight operations ROUTINE UA Any PIREP that contains weather phenomena not listed above including low level wind shear reports with air speed fluctuations ofless than 10 knots OV Location Use VHF NAVAIDs or an airport using the three or four letter location identifier Position can be over a site at some location relative to a site or along a route Ex OV ABC OV KFSM090025 OV OKC045020 DFW OV KABR KFSD TM Time Four digits in UTC Ex TM 0915 FL AltitudeFlight level Three digits for hundreds of feet with no space between FL and altitude If not known use UNKN Ex FL095 FL310 FLUNKN TP Aircraft type Four digits maximum if not known use UNKN Ex TP L329 TP B737 TP UNKN SK Sky cover Describes cloud amount height of cloud bases and height of cloud tops If unknown use UNKN Ex SK SCT040 TOP080 SK BKNUNKN TOP075 SK BKNOVC050 TOPUNKN SK SCT030 TOP060OVC 120 SK FEW030 SK SKC WX Flight visibility and weather Flight visibility FV reported first in standard METAR weather symbols Intensity for light no qualifier for moderate and for heavy shall be coded for all precipitation types except ice crystals and hail Ex WX FV05SM RA WX FV01SM SN BR IWX RA TA Temperature Celsius If below zero prefix with an M Temperature shall also be reported ificing is reported Ex TA 15 TA M06 WV Wind Direction from which the wind is blowing coded in tens of degrees using three digits Directions ofless than 100 degrees shall be preceded by a zero The wind speed shall be entered as a two or three digit group immediately following the direction coded in whole knots using the hundreds tens and units digits Ex IWV 27045KT IWV 280110KT TB Turbulence Use standard contractions for intensity and type CAT or CHOP when appropriate Include altitude only if different from FL See Table 3 3 Ex TB EXTRM TB OCNL LGTMOD BLW 090 TB MOD SEV CHOP 080110 IC Icing Describe using standard intensity and type contractions Include altitude only if different from FL See Table 3 4 Ex IC LGT MOD RIME IC SEV CLR 028045 RM Remarks Use free form to clarify the report putting hazardous elements first Ex RM LLWS 15 KT SFC030 DURC RWY22 JFK cing and turbuw ence reports state intensities using standard terminology when possible To lessen the chance of misinterpretation report icing and turbulence in standard terminology If a PIREP stated December 1999 PRETTY ROUGH AT 6500 SMOOTH AT 8500 PA24 there could be many interpretations of the strength of the turbulence at 6500 feet A report of light In oderate or severe turbulence at 6500 feet would have been more concise and understandable If a pilot s description of an icing or turbulence encounter cannot readily be translated into standard terminology the pilot s description should be transmitted verbatim TURBULEN CE The following table classi es each turbulence intensity according to its effect on aircraft control structural integrity and articles and occupants within the aircraft Pilots should report locations time UTC altitude aircraft type whether in or near clouds intensity and when applicable type CHOP clear air turbulence CAT and duration of turbulence Duration may be based on the time the pilot is ying between two locations or over a single location Highlevel turbulence normally above 15000 feet AGL that is not associated with cumuliform clouds including thunderstorms shall be reported as CAT Table 3 3 Turbulence Reporting Criteria Intensity Aircraft Reaction Reaction Inside Aircraft Light Turbulence that momentarily causes slight erratic Occupants may feel a slight changes in altitude andor attitude pitch roll strain against belts or shoulder yaw Report as light turbulence or light CAT straps Unsecured obj ects may or be displaced slightly Food Turbulence that causes slight rapid and somewhat service may be conducted and rhythmic bumpiness without appreciable changes little or no dif culty is in altitude or attitude Report as light CHOP encountered in walking Moderat Turbulence that causes changes in altitude andor Occupants feel definite strains e attitude occurs but the aircraft remains in positive against seat belts or shoulder control at all times It usually causes variations in straps Unsecured objects are indicated airspeed Report as moderate turbulence dislodged Food service and or moderate CAT walking are dif cult or Turbulence that is similar to light CHOP but of greater intensity It causes rapid bumps or jolts without appreciable changes in aircraft or attitude Report as moderate CHOP Severe Turbulence that causes large abrupt changes in Occupants are forced violently altitude andor attitude It usually causes large against seat belts or shoulder variations in indicated airspeed Aircraft may be straps Unsecured objects are momentarily out of control Report as severe tossed about Food service and turbulence or severe CAT walking are 39 39 39 Extreme Turbulence in which the aircraft is violently tossed about and is practically impossible to control It may cause structural damage Report as extreme turbulence or extreme CAT December 1999 ICING The following table classi es each icing intensity according to its operational effects on aircraft Pilots should report locations time UTC altitude aircraft type temperature and icing intensity and type rime clear or mixed Rirne ice is rough milky opaque ice formed by the instantaneous freezing of small supercooled water droplets Clear ice is a glossy clear or translucent ice formed by the relatively slow freezing of large supercooled water droplets Mixed ice is a combination of rime and clear ice Table 3 4 Icing Intensities Airframe Ice Accumulation and Pilot Report Intensity Airframe Ice A 39 quot Pilot Report Trace Ice becomes perceptible Rate of Location time altitudeFL accumulation slightly greater than rate of aircraft type temperature sublimation It is not hazardous even though and icing intensity and type deicinganti icing equipment is not used unless encountered for an extended period of time over 1 hour Light The rate of accumulation may create a Location time altitudeFL problem if flight is prolonged in this aircraft type temperature environment over 1 hour Occasional use of and icing intensity and type deicinganti icing equipment removesprevents accumulation It does not present a problem if the deicinganti icing equipment is used Moderate The rate of accumulation is such that even Location time altitudeFL short encounters become potentially aircraft type temperature hazardous and use of deicinganti icing and icing intensity and type or diversion is necessary Severe The rate of accumulation is such that Location time altitudeFL deicinganti icing equipment fails to reduce or control the hazard Immediate diversion is necessary aircraft type temperature and icing intensity and type EXAMPLES AND EXPLANATION S REFER TO TABLE 3 2 UUA OV ORDTM l235FLUNKNTP B727TB MODRM LLWS 20KT BLW 003 DURD RWY27L Urgent UA over Chicago O Hare Airport Chicago IL at 123 5Z Flight level is unknown but the information is from a Boeing 727 Turbulence was moderate and on descent to runway 27 left low level wind shear was detected below 300 feet Airspeed uctuations were plus and minus 20 knots December 1999 UUA OV ABQ090045TM 1430FL130TP BE30TB SEVRM BROKE ALL THE BOTTLES IN THE BAR An urgent UA 45 miles east of Albuquerque NM a pilot of a Beech King Air 300 reported severe turbulence at 13000 feet The pilot remarked the turbulence was so severe it broke all the bottles in the passenger cabin bar UA OV KMRBKPITTM 1600FL100TP BE55SK BKN024TOP032BKNOVC043TOPUNKN TA M12IC LGTMOD RIME 055080 This PIREP is decoded as follows UA Martinsburg to Pittsburgh Pennsylvania PA at 1600 UTC at 10000 feet MSL Type of aircraft is a Beechcraft Baron First cloud layer is broken with a base at 2400 feet MSL broken and tops at 3200 feet MSL The second cloud layer is broken to occasionally overcast with a base at 4300 feet MSL and tops unknown Outside air temperature is 12 degrees Celsius Light to moderate rime icing is reported between 5500 and 8000 feet MSL UA OV KOKC090064TM 1522FL080TP C172SK SCT090TOPUNKNWX FV05SM HZTA M04WV 24540KTTB LGTRM IN CLR This PIREP is decoded as follows UA 64 nautical miles east of Oklahoma City VOR at 1522 UTC ight level 8000 feet MSL Type of aircraft is a Cessna 172 There is a scattered cloud layer with bases at 9000 feet MSL and unknown tops Flight visibility is restricted to 5 statute miles due to haze Outside air temperature is 4 degrees Celsius wind is 245 degrees at 40 knots light turbulence and the aircraft is in clear skies UA OV KLITKFSMTM 0310FL100TP BE36SK SCT070TOP110TA M03WV 25015KT This PIREP is decoded as follows UA between Little Rock and Fort Smith Arkansas AR at 0310 UTC A Beech 36 is at 10000 feet MSL There is a scattered cloud layer with bases at 7000 feet MSL and tops at 11000 feet MSL The outside air temperature is 3 degrees Celsius Winds are from 250 degrees at 15 knots UA ov KABQTM 1845RM TIJERAS PASS CLSD DUE TO FG AND LOW CLDS UNA VFR RTN ABQ The PIREP is over Albuquerque at 1845 UTC The remark section indicates the Tijeras pass is closed due to fog and low clouds The pilot also mentions that shehe could not continue VFR and returned to Albuquerque UA OV KTOLTM 2200FL310TP B737TB MOD CAT 350390 This PIREP is decoded as follows UA over Toledo Ohio at 2200 UTC and ight level 310 a Boeing 737 reported moderate clear air turbulence between 35000 and 39000 feet MSL Nonmeteorological PIREPs sometimes help air traffic controllers This plain language report stated 3N PNS LARGE FLOCK OF BIRDS HDG GEN N MAY BE SEAGULLS FRMN This PIREP alerted pilots and controllers to a bird hazard December 1999 RADAR WEATHER REPORT SD General areas of precipitation including rain snow and thunderstorms can be observed by radar The radar weather report SD includes the type intensity and location of the echo top of the precipitation The intensity trend of precipitation is no longer coded on the SD It is important to remember that all heights are reported above MSL Table 35 explains symbols denoting intensity Radar stations report each hour at H35 Example of an SD TLX 1935 w TRW 8640 16460 20W C2425 MTS 570 AT 15965 AUTO a b c d e f g i quotMOl N02 0N3 PM34 9M3 RL2 j Above SD report decoded as follows a Location identi er and time of radar observation Oklahoma City SD at 1935 UTC b Echo pattern LN in this example The echo pattern or con guration may be one of the following 1 Line LN is a line of convective echoes with precipitation intensities that are heavy or greater at least 30 miles long at least 4 times as long as it is wide and at least 25 coverage within the line Area AREA is a group of echoes of similar type and not classi ed as a line Cell CELL is a single isolated convective echo such as a rain shower c Coverage in tenths of precipitation in the de ned area 8 10 in this example d Type and intensity of weather thunderstorm T with very heavy rainshowers RW WN Table 3 5 Precipitation Intensity December 1999 Table 3 6 Symbols Used in SD Sym bol Meaning R Rain RW Rain shower S Snow SW Snow shower T Thunderstorm Example of an SD TLX 1935 w TRW 864016460 20W C2425 MTS 570 AT 15965 AUTO a b c d e f g i quotMOl N02 0N3 PM34 9M3 RL2 j D Azimuth referenced to true north and range in nautical miles NM from the radar site of points de ning the echo pattern 8640 16460 in this echo For lines and areas there will be two azimuth and range sets that define the pattern For cells there will be only one azimuth and range set See the examples that follow for elaboration of echo patterns Dimension of echo pattern 20 NM wide in this example The dimension of an echo pattern is given when azimuth and range de ne m the center line of the pattern In this example 20W means the line has a total width of 20 NM 10 miles either side of a center line drawn from the points given in item e above Cell movement cells within line moving fr 240 degrees at 25 knots in this example Movement is only coded for cells it will not be coded for lines or areas Maximum top and location 57000 feet MSL on radial 159 degrees at 65 NM in this example Maximum tops may be coded with the symbols MT or MTS If it is coded with MTS it means that satellite data as well as radar information was used to measure the top of the precipitation The report is automated from WSRS 8D weather radar data Digital section is used for preparing radar summary chart Iquot Pquot UP I To aid in interpreting SDs the ve following examples are decoded into plain language GRB 1135 AREA 4TRW 9100 13075 50W C2425 MT 310 at 4547 AUTO Green Bay WI Automated SD at 1135 UTC An area of echoes 4 10 coverage containing thunderstorms and heavy rain showers Area is de ned by points referenced from GRB radar site at 9 degrees 100 NM and 130 degrees 75 NM These points plotted on a map and connected with a straight line de ne the center line of the echo pattern The width of the area is 50 NM ie 25 NM either side of the center line The cells are moving from 240 degrees at 25 knots Maximum top is 31000 feet MSL located at 45 degrees and 47 NM from GRB 37 December 1999 ICT 1935 LN 9TRWX 27580 21090 20W C2430 MTS 440 AT 26048 AUTO Wichita KS Automated SD at 1935 UTC A line of echoes 9 10 coverage containing thunderstorm with intense rain showers The center of the line extends from 275 degrees 80 NM to 210 degrees 90 NM The line is 20 NM wide NOTE To display graphically plot the center points on a map and connect the points with a straight line39 then plot the width Since the thunderstorm line is 20 miles wide it extends 10 miles either side of your plotted line The thunderstorm cells are moving from 240 degrees at 30 knots The maximum top is 44000 feet MSL at 260 degrees 48 NM from ICT GGW1135 AREA 3S 90120 15080 34W MT 100 at 13049 Glasgow MT Automated SD at 1135 UTC An area 3 10 coverage of light snow The area s centerline extends from points at 90 degrees 120 NM to 150 degrees 80 NM The area is 34 NM wide No movement was reported The maximum top is 10000 feet MSL at 130 degrees 49 NM MAP 1135 AREA 2TRW6R 67130 30845 105W C2240 MT 380 AT 6654 MidlandOdessa TX Automated SD at 1135 UTC An area of echoes total coverage 810 with 210 of thunderstorms with very heavy rainshowers and 6 10 coverage of light rain This suggests that the thunderstorms are embedded in an area of light rain The area lies 5212 miles either side of the line de ned by the two points 67 degrees 130 NM and 308 degrees 45 NM When an SD is transmitted but does not contain any encoded weather observation a contraction is sent which indicates the operational status of the radar Example TLX 1135 PPINE AUTO It is decoded as Oklahoma City OK s radar at 1135 UTC detects no echoes Table 3 7 Operational Status Contractions All SDs also contain groups of digits Example AM01 N01 0N3 PM34 QM3 RL2 SL1 These groups of digits are the final entry on the SD This digitized radar information is used primarily in preparing the radar summary chart However by using a proper grid overlay chart for the corresponding radar site this code is also useful in determining more precisely where the precipitation is occurring within an area as well as the intensity of the precipitation See Figure 31 for an example of a digital code plotted from the Oklahoma City OK SD 38 December 1999 The digit assigned to a box represents the intensity of precipitation as determined by the WSR 88D and is the maximum precipitation intensity found within the grid box See Table 72 for de nitions of precipitation intensities associated with digits 1 through 6 These digits were once commonly referred to as VIP levels because precipitation intensity and therefore the digits was derived using a video integrator processor VIP Since the WSR 88D and not the video integrator processor is now used to determine precipitation intensity it is suggested that the term VIP should no longer be used when describing precipitation intensity For example if a speci c grid has the number 2 associated with it that grid would be described as having moderate precipitation not VIP level 2 precipitation A box is identi ed by two letters the rst representing the row in which the box is found and the second letter representing the column For example M01 identi es the box located in row M and column 0 as containing light precipitation A code of M01234 indicates precipitation in four consecutive boxes in the same row Working from left to right box MO 1 box MP 2 MQ 3 and box MR 4 When using hourly SDs in pre ight planning note the location and coverage of echoes the type of weather reported the intensity and especially the direction of movement It is important to remember that the SD contains information pertaining to the location of particles in the atmosphere that are of precipitation size or larger It does not display locations of cloudsize particles and therefore neither ceilings nor restrictions to visibility An area may be blanketed with fog or low stratus but the SD would not include information about it Pilots should use SDs along with METARs satellite photos and forecasts when planning a ight The SDs help pilots plan ahead to avoid thunderstorm areas Once airborne however pilots must depend on contact with Flight Watch which has the capability to display current radar images airborne radar or visual sighting to evade individual storms December 1999 Figure 31 Digital Radar Report Plotted on a PPI Grid Overlay Chart Note See Table 72 for Intensity Level Codes 1 through 6 310 December 1999 SATELLITE WEATHER PICTURES Prior to weather satellites weather observations were made only at distinct points within the atmosphere and supplemented by PIREPs These PIREPs gave a sense of weather as viewed from above However with the advent of weather satellites a whole new dimension to weather observing and reporting has emerged There are two types of weather satellites in use by the U S today P y Cr 39 39 F 39 39 Satellite GOES which is a geostationary satellite and the Polar Orbiter Environmental Satellite POES Additional satellite imagery is available from the European Meteosat and the Japanese GMS geostationary satellites Two US GOES satellites are used for imaging One is stationed over the equator at 75 degrees west longitude and is referred to as GOES EAST since it covers the eastern US The other is positioned at 135 degrees west longitude and is referred to as GOES WEST since it covers the western US Together they cover North and South America and surrounding waters They normally transmit an image of Earth pole to pole every 15 minutes When disastrous weather threatens the US the satellites can scan small areas rapidly so that a picture can be received as often as every 1 minute Data from these rapid scans are used at NWS offices Since the GOES satellite is stationary over the equator the images poleward of about 50 degrees latitude become greatly distorted For images above 50 degrees latitude polar orbiting satellites are employed The NOAA satellite is a polar orbiter and orbits the earth on a track that nearly crosses the North and South poles A high resolution picture is produced about 500 miles either side of its track on the journey from pole to pole The NOAA pictures are essential to weather personnel in Alaska and Canada Two types of imagery are available from satellites and when combined give a great deal of information about clouds Through interpretation the analyst can determine the type of cloud the temperature of cloud tops from this the approximate height of the cloud can be determined and the thickness of cloud layers From this information the analyst gets a good idea of the associated weather One type of imagery is visible Figure 32 Avisible image shows clouds and Earth re ecting sunlight to the satellite sensor The greater the re ected sunlight reaching the sensor the whiter the object is on the picture The amount of re ectivity reaching the sensor depends upon the height thickness and ability of the object to re ect sunlight Since clouds are much more re ective than most of the Earth clouds will usually show up white on the picture especially thick clouds Thus the visible picture is primarily used to determine the presence of clouds and the type of cloud from shape and texture Due to the obvious lack of sunlight there are no visible images available at night The second type of imagery is infrared IR Figure 33 An IR picture shows heat radiation being emitted by clouds and Earth The images show temperature differences between cloud tops and the ground as well as temperature gradations of cloud tops and along the Earth s surface Ordinarily cold temperatures are displayed as light gray or white High clouds appear the whitest However various computergenerated enhancements are sometimes used to sharply illustrate important temperature contrasts IR images measure cloud top temperatures and are used to approximate the height of clouds From this one can see the importance of using visible and IR imagery together when interpreting clouds IR images are available both day and night December 1999 Satellite images are processed by the NWS as well as by many private companies Therefore they can be received from many different sources Depending upon the source satellite images may be updated anywhere from every 15 minutes to every hour therefore it is important to note the time on the images when interpreting them By viewing satellite images the development and dissipation of weather can be seen and followed over the entire country and coastal regions NESDIS is developing the capability to provide derived products useful to aviation from satellite data These experimental products are available via the Internet and include 1 Fog and low cloud coverage and depth 2 Volcanic ash detection 3 Microburst products 4 Soundings 5 Clear air turbulence 6 Aircraft icing potential December 1999 gure 72 Vmble Satellite Imagery 3713 Decanber 1999 Figure 373 In ared Satellite Irragery December 1999 RADIOSONDE ADDITIONAL DATA gRADAng Radiosonde Additional Data RADATs information is obtained from the radiosonde observations that are conducted twice a day at 00 and 12Z The information contained in a RADAT is the observed freezing level and the relative humidity associated with the freezing level The freezing level is the height above MSL at which the temperature is zero degrees Celsius The format associated with the RADAT is as follows Stn 1D Time RADAT UU D hhhhhhhhhn Explanation Stn 1D and Time standard threeletter identi er and observation time in UTC RADAT a contraction identifying the data as freezinglevel data UU relative humidity at the freezing level in percent When more than one level is identi ed UU is the highest relative humidity observed at any of the levels transmitted D a coded letter L M or H used in the event of multiple freezing levels to identify which level has the highest relative humidity L 7 lowest M 7 middle H 7 highest This letter is omitted when only one level is coded hhh 7 height of the freezing level in hundreds of feet Up to three freezing levels can be speci ed in the event of multiple freezing levels If there are more than three freezing levels the levels coded are the lowest highest and the intermediate level with the highest relative humidity n 7 an indicator to show the number of freezing levels in addition to the three which are coded The number is omitted when all observed freezing levels are coded three or less Examples SJU 1200 RADAT 87160 The San Juan Puerto Rico RADAT indicates that the freezing level was 16000 feet MSL and the relative humidity was 87 at the freezing level 16000 Mean Sea Level I 0 C Figure 3439SJU RADAT 315 December 1999 Section 4 AVIATION WEATHER FORECASTS Good ight planning involves considering all available weather information including weather forecasts This section explains the following aviation forecasts 1 Aviation Terminal Forecast TAF 2 Aviation Area Forecast FA 3 In ight Aviation Weather Advisories 4 Alaska Gulf of Mexico and International Area Forecasts FAs 5 Transcribed Weather Broadcasts TWEB Text Products 6 Winds and Temperatures Aloft Forecast FD 7 Center Weather Service Unit CWSU Products Also discussed are the following general forecasts that may aid in ight planning 1 Hurricane Advisory WH 2 Convective Outlook AC 3 Severe Weather Watch Bulletins WW and Alert Messages AWW AVIATION TERMINAL FORECAST TAF An Aviation Terminal Forecast TAF is a concise statement of the expected meteorological conditions within a 5statutemile radius from the center of an airport s runway complex during a 24hour time period The TAFs use the same weather code found in METAR weather reports Detailed explanations of the code are found only in Section 2 The National Weather Service NWS requires an airport to have two consecutive METAR observations not less than 30 minutes apart nor more than 1 hour apart before a TAF will be issued After the TAF has been issued the forecaster will use all available weather data sources to maintain the TAF If during this time a METAR is missing or part of the METAR is missing the forecaster can use other weather sources to obtain the necessary data to maintain the TAF However if the forecaster feels that the other weather sources cannot provide the necessary information the forecaster will discontinue the TAF A TAF contains the following elements in the order listed Type of report ICAO station identi er Date and time of origin Valid period date and time Wind forecast Visibility forecast Signi cant weather forecast Sky condition forecast Nonconvective lowlevel wind shear forecast optional data Forecast change indicators Probability forecast HH WSQM WNH 939 December 1999 International and US military TAFs also contain forecasts of maximum and minimum temperature icing and turbulence These three elements are not included in NWSprepared TAFs For forecast icing and turbulence see page 423 In ight Aviation Weather Advisories The following paragraphs describe the elements in a TAF report A sample report will accompany each element with the subject element in bold letters TYPE OF REPORT TAF KPIR111140Z 111212 13012KT P6SM BKN100 WS02035035KT TEMPO 1214 5SM BR FM1500 16015G25KT P6SM SCT040 BKN250 FM0000 14012KT P6SM BKN080 OVC150 PROB40 0004 3SM TSRA BKN030CB FM0400 14008KT P6SM SCT040 OVC080 TEMPO 0408 3SM TSRA OVC030CB BECMG 0810 32007KT The report type header will always appear as the rst element in the TAF There are two types of TAF reports a routine forecast TAF and an amended forecast TAF AMD An amended TAF is issued when the forecaster feels the TAF is not representative of the current or expected weather conditions An equal sign at the end of the TAF signifies the end of the report ICAO STATION IDENTIFIER TAF KPIR 111140Z 111212 13012KT P6SM BKN100 WS0203503 5KT TEMPO 1214 5SM BR FM1500 16015G25KT P6SM SCT040 BKN250 FM0000 14012KT P6SM BKN080 OVC150 PROB40 0004 3SM TSRA BKN030CB FM0400 14008KT P6SM SCT040 OVC080 TEMPO 0408 3SM TSRA OVC030CB BECMG 0810 32007KT The TAF code uses ICAO fourletter location identi ers as described in Section 2 TAF locations are in Figures 41 42 43 and 44 located on pages 413 through 416 DATE AND TIME OF ORIGIN TAF KPIR 111140Z 111212 13012KT P6SM BKN100 WS02035035KT TEMPO 1214 5SM BR FM1500 16015G25KT P6SM SCT040 BKN250 FM0000 14012KT P6SM BKN080 OVC150 PROB40 0004 3SM TSRA BKN030CB FM0400 14008KT P6SM SCT040 OVC080 TEMPO 0408 3SM TSRA OVC030CB BECMG 0810 32007KT This element is the date and universal coordinated time UTC the forecast is actually prepared The format is a twodigit date and fourdigit time followed without a space by the letter Z Routine TAFs are prepared and filed approximately onehalf hour prior to scheduled issuance times Examples 111140Z Forecast prepared on the eleventh day of the month at 1140Z 050530Z Forecast prepared on the fth day of the month at 0530Z December 1999 VALID PERIOD DATE AND TIME TAF KPIR111140Z 111212 13012KT P6SM BKN100 WS02035035KT TEMPO 1214 SSM BR FM1500 16015G25KT P6SM SCT040 BKN250 FM0000 14012KT P6SM BKN080 OVC150 PROB40 0004 3SM TSRA BKN030CB FM0400 14008KT P6SM SCT040 OVC080 TEMPO 0408 3SM TSRA OVC030CB BECMG 0810 32007KT The valid period of the forecast is a twodigit date followed by the twodigit beginning and twodigit ending hours in UTC Routine TAFs are valid for 24 hours and are issued four times daily at 0000Z 0600Z 1200Z and 1800Z All ending times throughout the TAF of 00Z are indicated by the number 24 Examples 111212 Forecast valid from the eleventh at 12Z to the twelfth at 12Z 300024 Forecast valid from the thirtieth at 00Z to the rst at 00Z Amended canceled or delayed forecasts may have valid periods less than 24 hours Examples 231512 Forecast valid from the twentythird at 15Z to the twentyfourth at 12Z 091006 Forecast valid from the ninth at 10Z to the tenth at 06Z For airports with less than 24hour observational coverage for which parttime terminal forecasts are provided the TAF will be valid until the end of the scheduled forecast even if the observations have ceased before that time AND NOT SKED amendment not scheduled or NIL AND no amendment will be issued after the forecast information AND NOT SKED AFT closing timeZ amendment not scheduled after closing timeZ will be used if the times of the observations are known and judged reliable During the time the station is closed and a TAF is issued there will be no forecast as indicated by NIL no TAF after the valid date and time group Only after two METARs observations have been disseminated will a TAF be issued AMD LTD TO CLD VIS AND WIND amendment limited to clouds visibility and wind is used at observation sites that have parttime manual augmentation This remark means that there will be amendments only for clouds visibility and wind There will be Q A f f A A amendments for quot or WIND FORECAST TAF KPIR111140Z 111212 13012KT P6SM BKN100 WS02035035KT TEMPO 1214 SSM BR FM1500 16015G25KT P6SM SCT040 BKN250 FM0000 14012KT P6SM BKN080 OVC150 PROB40 0004 3SM TSRA BKN030CB FM0400 14008KT P6SM SCT040 OVC080 TEMPO 0408 3SM TSRA OVC030CB BECMG 0810 32007KT The surface wind forecast is the wind direction in degrees from true north first three digits and mean speed in knots last two or three digits if 100 knots or greater The contraction KT denotes the units of wind speed in knots Wind gusts are noted by the letter G appended to the mean wind speed followed by the highest expected gust two or three digits if 100 knots or greater Calm winds are encoded as 00000KT A variable wind is encoded as VRB when wind direction uctuates due to convective activity or low wind speeds 3 knots or less December 1999 Exam les 13012KT 18010KT 35012G26KT or VRB16G28KT VISIBILITY FORECAST TAF KPIR111140Z 111212 13012KT P6SM BKN100 WSO2035035KT TEMPO 1214 5SM BR FM1500 16015G25KT P6SM SCT040 BKN250 FM0000 14012KT P6SM BKN080 OVC150 PROB40 0004 3SM TSRA BKN030CB FM0400 14008KT P6SM SCT040 OVC080 TEMPO 0408 3SM TSRA OVC030CB BECMG 0810 32007KT The prevailing visibility is forecasted in whole and fractions of statute miles followed by SM to note the units of measurement Statute miles followed by fractions of statute miles are separated with a space for example 1 12SM Forecasted visibility greater than 6 statute miles is indicated by coding P6SM If prevailing visibility is 6 statute miles or less one or more weather phenomena must be included in the signi cant weather forecast If volcanic ash is forecasted the visibility must also be forecasted even if the visibility is greater than 6 statute miles Sector or variable visibility is not forecasted Examples 12SM 2 14SM SSM or P6SM SIGNIFICANT WEATHER FORECAST TAF KPIR111140Z 111212 13012KT P6SM BKN100 WSO2035035KT TEMPO 1214 SSM BR FM1500 16015G25KT P6SM SCT040 BKN250 FM0000 14012KT P6SM BKN080 OVC150 PROB40 0004 3SM TSRA BKN030CB FM0400 14008KT P6SM SCT040 OVC080 TEMPO 0408 3SM TSRA OVC030CB BECMG 0810 32007KT The expected weather phenomenon or phenomena are coded in TAF reports using the same format quali ers and phenomena contractions as METAR reports except UP See Section 2 Obscurations to vision will be forecasted whenever the prevailing visibility is forecasted to be 6 statute miles or less Precipitation and volcanic ash will always be included in the TAF regardless of the visibility forecasted Examples FM2200 18005KT 1SM BR SKC FMO 100 12010KT P6SM RA BKN020 FM1500 22015KT P6SM VA SCT100 If no signi cant weather is expected to occur during a speci c time period in the forecast the weather group is omitted for that time period However if after a time period in which signi cant weather has been forecasted a change to a forecast of no signi cant weather occurs the contraction N SW no signi cant weather will appear as the weather included in BECMG or TEMPO groups NSW will not be used in the initial time period of a TAF or in FM groups December 1999 Example FM0600 16010KT 3SM RA BKN030 BECMG 0810 P6SM NSW If the forecaster determines that in the vicinity of the airport there could be weather that impacts aviation the forecaster will include those conditions after the weather group The letters VC describe conditions that will occur within the vicinity of an airport 510 SM and will be used only with fog showers or thunderstorms FG SH or TS Examples P6SM VCFG fog in the vicinity 5SM BR VCSH showers in the vicinity P6SM VCTS thunderstorms in the vicinity SKY CONDITION FORECAST TAF KPIR111140Z 111212 13012KT P6SM BKN100 wso2035035KT TEMPO 1214 5SM BR FM1500 16015G25KT P6SM SCT040 BKN250 FMOOOO 14012KT P6SM BKN080 ovc150 PROB40 0004 3SM TSRA BKN030CB FM0400 14008KT P6SM SCT040 ovcoso TEMPO 0408 3SM TSRA OVC030CB BECMG 0810 32007KT TAF sky condition forecasts use the METAR format described in Section 2 Cumulonimbus clouds CB are the only cloud type forecasted in TAFs Examples BKN100 SCT040 BKN030CB or FEW008 BKN015 When the sky is obscured due to a surfacebased phenomenon vertical visibility VV into the obscuration is forecasted The format for vertical visibility is VV followed by a threedigit height in hundreds of feet Partial obscurations are not forecasted Remember a ceiling is the lowest broken or overcast layer or vertical visibility Example VV008 NONCONVECTIVE LOW LEVEL WIND SHEAR FORECAST OPTIONAL DATA TAF KPIR111140Z 111212 13012KT P6SM BKN100 WS02035035KT TEMPO 1214 5SM BR FM1500 16015G25KT P6SM SCT040 BKN250 FM0000 14012KT P6SM BKN080 OVC150 PROB40 0004 3SM TSRA BKN030CB FM0400 14008KT P6SM SCT040 OVC080 TEMPO 0408 3SM TSRA OVC030CB BECMG 0810 32007KT A forecast of nonconvective lowlevel wind shear is included immediately after the cloud and obscuration group when wind shear criteria have been or will be met The forecast includes the height of the wind shear followed by the wind direction and wind speed at the indicated height Height is given in hundreds of feet above ground level AGL up to and including 2000 feet Wind shear is encoded with the contraction WS followed by a threedigit height solidus l and winds at the height indicated in the same format as surface winds The wind shear element is omitted if not expected to occur 45 December 1999 Example WS02036035KT FORECAST CHANGE INDICATORS TAF KPIR111140Z 111212 13012KT P6SM BKN100 WS02035035KT TEMPO 1214 5SM BR FM1500 16015G25KT P6SM SCT040 BKN250 FM0000 14012KT P6SM BKN080 OVC150 PROB40 0004 3SM TSRA BKN030CB FM0400 14008KT P6SM SCT040 OVC080 TEMPO 0408 3SM TSRA OVC030CB BECMG 0810 32007KT If a signi cant change in any of the elements is expected during the valid period a new time period with the changes is included The following change indicators are used when either a rapid gradual or temporary change is expected in some or all of the forecasted meteorological conditions From FM Group The FM group is used when a m and signi cant change usually occurring in less than 1 hour in prevailing conditions is expected Appended to the FM indicator is the fourdigit hour and minute the change is expected to begin The forecast is valid until the next change group or until the end of the current forecast The FM group will mark the beginning of a new line in a TAF report Each FM group shall contain a forecast of wind visibility weather if signi cant sky condition and wind shear if warranted FM groups will not include the contraction NSW Examples FM1500 16015G25KT PGSM SCT040 BKN250 FM0200 32010KT 3SM TSRA FEW010 BKN030CB Becoming BECMG Group The BECMG group is used when a gradual change in conditions is expected over a period not to exceed 2 hours The time period when the change is expected to occur is a fourdigit group containing the beginning and ending hours of the change that follows the BECMG indicator The gradual change will occur at an unspeci ed time within the time period Only the changing forecasted meteorological conditions are included in BECMG groups Omitted conditions are carried over from the previous time group Example FM2000 18020KT PGSM BKN030 BECMG 0103 OVC015 This BECMG group describes a gradual change in sky condition from BKN030 to OVC015 The change in sky conditions occurs between 01Z and 03Z Refer back to the FM2000 group for the wind and visibility conditions The forecast after 03Z will be 18020KT P6SM OVC015 December 1999 Example FM0400 14008KT PGSM SCT040 OVC080 TEMPO 0408 3SM TSRA OVC030CB BECMG 0810 32007KT This BECMG group describes a gradual change in wind direction only beginning between 08Z and 10Z Refer back to the previous forecast group in this case the FM0400 group for the prevailing visibility weather and sky conditions The forecast after 10Z will be 32007KT P6SM SCT040 OVC080 Temporary TEMPO Group The TEMPO group is used for temporary uctuations of wind visibility weather or sky condition that are expected to last for generally less than an hour at a time occasional and expected to occur during less than half the time period The TEMPO indicator is followed by a fourdigit group giving the beginning and ending hours of the time period during which the temporary conditions are expected Only the changing forecasted meteorological conditions are included in TEMPO groups The omitted conditions are carried over from the previous time group Example FM1000 27005KT PGSM SKC TEMPO 1216 3SM BR This temporary group describes visibility and weather between 12Z and l6Z The winds and sky condition have been omitted Go back to the previous forecast group FM1000 to obtain the wind and sky condition forecast The forecast between 12Z and l6Z is 27005KT 3SM BR SKC Example FM0400 14008KT PGSM SCT040 OVC080 TEMPO 0408 3SM TSRA OVC030CB BECMG 0810 32007KT This temporary group describes visibility weather and sky condition between 04Z and 08Z The winds have been omitted Go back to the previous forecast group FM0400 to obtain the wind forecast The forecast between 04Z and 08Z is l4008KT 3SM TSRA OVC030CB PROBABILITY PROB30 or PROB40 FORECAST TAF KPIR 1111402 111212 13012KT P6SM BKN100 wso2035035KT TEMPO 1214 SSM BR FM1500 16015G25KT P6SM SCT040 BKN250 FM0000 14012KT P6SM BKN080 ovc150 PROB40 0004 3SM TSRA BKN030CB FM0400 14008KT P6SM SCT040 ovcoso TEMPO 0408 3SM TSRA OVC030CB BECMG 0810 32007KT The probability forecast describes the probability or chance of thunderstorms or other precipitation events occurring along with associated weather conditions wind visibility and sky conditions The probability forecast will not be used in the first 6 hours of the TAF The PROB30 or PROB40 group is used when the of quot 39 or 391 quot quot is in the 30 to less than 40 or 40 to less than 50 range r quot 39 Ifthe quot 39 or J 391 quot quot chance is greater than 50 it is considered a prevailing weather condition and is included in the signi cant weather section or the TEMPO change indicator group PROB30 or PROB40 is followed by a fourdigit time group giving the beginning and ending hours of the time period during which the thunderstorms or precipitation is expected 47 December 1999 Example FM0600 0915KT PGSM BKN020 PROB30 1014 ISM RA BKNO 15 This example depicts a 30 to less than 40 chance of 1statute mile moderate rain and a broken cloud layer ceiling at 1500 feet between the hours of 1014Z Example FM0000 14012KT PGSM BKN080 OVC150 PROB40 0004 3SM TSRA BKN030CB In this example there is a 40 to lt50 chance of Visibility 3 statute miles thunderstorms with moderate rain showers and a broken cloud layer ceiling at 3000 feet with cumulonimbus between the hours of 0004Z December 1999 EXAMPLES OF TAF REPORTS TAF KPIR 111140Z 111212 13012KT P6SM BKN100 WS02035035KT TEMPO 1214 SSM BR FM1500 16015G25KT P6SM SCT040 BKN250 FM0000 14012KT P6SM BKN080 OVC150 PROB40 0004 3SM TSRA BKN030CB FM0400 14008KT P6SM SCT040 OVC080 TEMPO 0408 3SM TSRA OVC030CB BECMG 0810 32007KT TAF Aviation terminal forecast KPIR Pierre South Dakota 111140Z prepared on the 113911 at 1140Z 111212 valid period from the 11 h at 12002 until the 12 h at 12002 13012KT wind 130 at 12 knots P6SM visibility greater than 6 statute miles BKN 100 ceiling 10000 broken WS02035035KT wind shear at 2000 feet wind at 2000 feet from 350 at 35 knots TEMPO 1214 temporary conditions between 1200Z and 1400Z SSM visibility 5 statute miles BR mist FM1500 from 1500Z 16015G25KT wind 160 at 15 knots gusting to 25 knots P6SM visibility greater than 6 statute miles SCT040 BKN250 4000 scattered ceiling 25000 broken FM0000 from 0000Z 14012KT wind 140 at 12 knots P6SM visibility greater than 6 statute miles BKN080 OVC150 ceiling 8000 broken 15000 overcast PROB40 0004 40 probability between 0000Z and 0400Z 3SM visibility 3 statute miles thunderstorm with moderate rain showers BKN030CB ceiling 3000 broken with cumulonimbus FM0400 from 0400Z 14008KT wind 140 at 8 knots P6SM visibility greater than 6 statute miles SCT040 OVC080 4000 scattered ceiling 8000 overcast TEMPO 0408 temporary conditions between 0400Z and 0800Z 3SM visibility 3 statute miles TSRA thunderstorms with moderate rain showers OVC030CB ceiling 3000 overcast with cumulonimbus BECMG 0810 becoming between 0800Z and 1000Z 32007KT wind 320 at 7 knots the equal sign signi es the end of the TAF December 1999 TAF AMD KEYW 131555Z 131612 VRB03KT P6SM VCTS SCT025CB BKN250 TEMPO 1618 2SM TSRA BKN 020C B FM1800 VRB03KT P6SM SCT025 BKN250 TEMPO 2024 ISM TSRA OVC010CB FM0000 VRB03KT P6SM VCTS SCT020CB BKN 120 TEMPO 0812 BKN020CB TAF AMD KEYW 131555Z 131612 VRB03KT P6SM VCTS SCT025CB BKN250 TEMPO 1618 2SM TSRA BKN020CB FM1800 SCT025 BKN250 TElVlPO 2024 ISM TSRA OVC010CB FM0000 VRB03KT P6SM VCTS SCT020CB BKN120 TElVlPO 0812 BKN020CB the Amended aviation terminal forecast Key West Florida prepared on the 133911 at 1555Z valid period from the 13 11 at 1600Z until the 14 11 at 1200Z wind variable at 3 knots visibility greater than 6 statute miles thunderstorms in the vicinity 2500 scattered with cumulonimbus ceiling 25000 broken temporary conditions between 1600Z and 1800Z visibility 2 statute miles thunderstorms with moderate rain showers ceiling 2000 broken with cumulonimbus from 1800Z wind variable at 3 knots visibility greater than 6 statute miles 2500 scattered ceiling 25000 broken temporary conditions between 2000Z and 0000Z visibility 1 statute mile thunderstorms with moderate rain showers ceiling 1000 overcast with cumulonimbus from 0000Z variable wind at 3 knots visibility greater than 6 statute miles thunderstorms in the vicinity 2000 scattered with cumulonimbus ceiling 12000 broken temporary conditions between 0800Z and 1200Z ceiling 2000 broken with cumulonimbus the equal sign signi es the end of TAF 410 TAF December 1999 KCRP 111730Z 111818 19007KT P6SM SCT030 TEMPO 1820 BKN040 FM2000 16011KT P6SM VCTS FEW030CB SCT250 FM0200 14006KT P6SM FEW025 SCT250 FM0800 VRB03KT SSM BR SCT012 TEMPO 1012 12SM FG BKN001 FM1500 17007KT P6SM SCT025 TAF KCRP 111730Z 11 1818 19007KT P6SM SCT030 TEMPO 1820 BKN 040 FM2000 16011KT P6SM VCTS FEW030CB SCT250 FM0200 14006KT P6SM FEW025 SCT250 SCTO 12 TEMPO 1012 12SM FG BKN 001 FM1500 17007KT P6SM SCT025 Aviation terminal forecast Corpus Christi Texas prepared on the 113911 at 173 OZ valid period from the 11 11 at 1800Z until the 12 11 at 1800Z wind 190 at 7 knots visibility greater than 6 statute miles 3000 scattered temporary conditions between 1800Z and 2000Z ceiling 4000 broken from 2000Z wind 160 at 11 knots visibility greater than 6 statute miles thunderstorms in the vicinity 3000 few with cumulonimbus 25000 scattered from 0200Z wind 140 at 6 knots visibility greater than 6 statute miles 2500 few 25000 scattered from 0800Z wind variable at 3 knots visibility 5 statute miles mist 1200 scattered temporary conditions between 1000Z and 1200Z visibility 12 statute mile fo ceiling 100 broken from 1500Z wind 170 at 7 knots visibility greater than 6 statute miles 2500 scattered the equal sign signifies the end of the TAF 411 December 1999 TAF KACK 112340Z 120024 29008KT P6SM SKC BECMG 1618 22015KT TAF Aviation terminal forecast KACK Nantucket Massachusetts 112340Z prepared on the 113911 at 2340Z 120024 valid period from the 12 h at 00002 until the 13 h at 00002 29008KT wind 290 at 8 knots P6SM visibility greater than 6 statute miles SKC sky clear BECMG 1618 becoming between l600Z and 1800Z 22015KT wind 220 at 15 knots the equal sign signifies the end of the TAF TAF KMWH 200535Z 200606 NIL TAF Aviation terminal forecast KMWH Moses Lake Washington 200535Z prepared on the 203911 at 0535Z 200606 valid period from the 20 11 at 0600Z to the 21st at 0600Z NIL no TAF the equal sign signifies the end of the TAF 412 m7 mBEm 335 macawqu 8883 89804 EH 7 035 I I 017 ltv o uu ammumau umuwnmm y 553 Human I we 5 22 ozmom 5 I251 301I I w3lt 5 1 X IVEIE I F041 LBW I Ivzv I I IE I53 5 quot9 I I EFL EZO I v Incrx 2201 I 2211 I Iw0v 25 I I89 Iwgt9 gt Z wng I I 005 I 33 v O I 0101 35 mgtv I Inimv quot59 I 52v 033 3 OO moogI 093 ImmS quotES 59 I zme I019 Imam ODD I Bu I I000 I 221 ltLv I 115 I 251 I I 4mm I quot 05 121 040v MOE I I D 9 v29 I59 093 I cum gt2 5 I049 55 II I ozEI EU 29 I95 I89 gt292 993 ovI 02ng IZDIV IMgtv IvEOv gtmv I I Es C Invl I402 032v ZDWxI 205 I Equot quot2ng 09 I IE5 D m I mnlt Ozmv I l Mv mv Ear v I 03m I mvI sgtvI I25 55 I 39 mmvI I 95 van IIIov xl m2 I I wmvl vnvl 5L 0 Z IvEUv FOExl ZWEI gt Igtgtv 2411 I OWE I LPG I EgtI I 82 3588 E4 m m SHED mSOSWESU E mwm mnouwooq QB aw MERE IEmz 595 Human o Dzmwm quot 4 di 0 won I Imuix Xmltxl llm E v I INSV mcuz Sui azag LMUKOODEUX cmrvi LOWXI Ogt nuzt ox w9llllri a n 249 Ham soquot 09 E1 n55 umvl I hmmv ammo Issox SE I254 I349 lama 2 3885 December 1999 GUAM PGSN Saipan Mariana Is 039 PGUM Agana Guam Mariana Is o PTYA Yap Micronesia PTPN l PTRO PTKK39 Pohnpei Micronesia Koror Palau ls Chuuk MicroneSIa PUERTO RICO AND THE VIRGIN ISLANDS TJBQ TJSJ 39 P TJMZ 1 TIST Mayaguez St Thomas a TNCM Phillipsburg St Maarten IIIoFI1e 9 TISX Christiansted St Croix Q TKPK Basseterre St Kitts Figure 43 TAF Locations Guam and Puerto Rico 415 December 1999 4H PASN C n D y i unu ALASKA LOCATIONS a GM PHNL PHMK PHOG PHN VE PHJH TAFs alsu plepaled luvlhe lulluwlng by Hunululu nut planed un map PJON r Juhnslu d N 55 31W PTSA r Kusme he I 5 CNN 1431 HE PKWAV Kwajaleln Malshall Is 3 43N 57 431E PKMJ r Majum Malshall Is 7 quotSN 17 23E NSTU r Pagn PaguAm21 Samna 14 2m 1m 43w PHKO PWAK W kE Island 1517N 155 35E HAWAII LOCATIONS Figure 44 TAF Locations Alaska and Hawaii December 1999 AVIATION AREA FORECAST gFA An Aviation Area Forecast FA is a forecast of visual meteorological conditions VMC clouds and general weather conditions over an area the size of several states To understand the complete weather picture the FA must be used in conjunction with the inflight aviation weather advisories Together they are used to determine forecast en route weather and to interpolate conditions at airports for which no TAFs are issued Figure 45 on page 421 maps the FA areas The FAs are issued 3 times a day by the Aviation Weather Center AWC in Kansas City Missouri for each of the 6 areas in the contiguous 48 states The weather forecast office WFO in Honolulu issues FAs for Hawaii as shown in Figure 46 on page 422 Alaska FA information is on page 427 There are also two specialized FAs one for the Gulf of Mexico and one for intemational airspace This is a partial example of an FA which will be used in this section DFWC FA 120945 SYNOPSIS AND VFR CLDSWX SYNOPSIS VALID UNTIL 130400 CLDSWX VALID UNTIL 122200OTLK VALID 122200130400 OK TX AR TN LA MS AL AND CSTL WTRS SEE AIRMET SIERRA FOR IFR CONDS AND MTN OBSCN TS IlVlPLY SEV OR GTR TURB SEV ICE LLWS AND IFR CONDS NON MSL HGTS DENOTED BY AGL OR CIG SYNOPSISLOW PRES TROF 10Z OKTX PNHDL AREA FCST MOV EWD INTO CNTRLSWRN OK BY 04Z WRMFNT 10Z CNTRL OKSRN ARNRN MS FCST LIFT NWD INTO NERN OK NRN AR XTRM NRN MS BY 04Z S CNTRL AND SERN TX AGL SCTBKN010 TOPS 030 VIS 35SM BR l4 16Z BECMG AGL SCT030 19Z AGL SCT050 OTLKVFR OK PNHDL AND NWAGL SCT030 SCTBKN100 TOPS FL200 15Z AGL SCT040 SCT100 AFT 20Z SCT TSRA DVLPGFEW POSS SEV CB TOPS FL450 OTLKVFR SWRN OKCIG BKN020 TOPS 050 VIS 35SM BR 14Z AGL SCTBKN040 18Z CIG BKN060 TOPS FL180 22Z SCT TSRA DVLPGFEW POSS SEV CB TOPS ABV FL450 OTLKVFR NERN QTRCIG BKN020 OVC050 VIS 35SM NMRS TSRAFEW POSS SEV CB TOPS ABV FL450 15Z AGL SCT030 SCTBKN100 TOPS FL250 18Z AGL SCT040 OTLKVFR SERN QTRAGL SCTBKN020 TOPS 050 18Z AGL SCT040 OTLKVFR CSTL WTRS LA MS AL WTRSSCT025 SCTBKN080 TOPS 150 ISOL TSRA CB TOPS FL350 OTLKVFR TX WTRSSCT CI OCNL SCT030 OTLKVFR 417 December 1999 The FA is comprised of four sections a communications and product header section a precautionary statements section and two weather sections a synopsis section and a visual ight rules VFR cloudsweather section COMMUNICATIONS AND PRODUCT HEADER The communications and product header identifies the of ce for which the FA is issued the date and time of issue the product name the valid times and the states andor areas covered by the FA The following shows the communications and product header for the example FA shown on page 417 DFWC FA 120945 SYNOPSIS AND VFR CLDSWX SYNOPSIS VALID UNTIL 130400 CLDSWX VALID UNTIL 122200OTLK VALID 122200130400 OK TX AR TN LA MS AL AND CSTL WTRS In the rst line DFW indicates the area for which the FA is valid The C indicates VFR clouds and weather while the FA indicates what type of forecast message it is The 120945 indicates the date and time the FA was issued The next line SYNOPSIS AND VFR CLDSW states what information is contained in this forecast message SYNOPSIS VALID UNTIL 130400 means the synopsis section of the FA is valid until the thirteenth at 0400Z The CLDSWX VALID UNTIL 122200OTLK VALID 122200130400 statement indicates the forecast section is valid until the twelfth at 2200Z while the outlook portion is valid from the twelfth at 2200Z until the thirteenth at 0400Z OK TX AR TN LA MS AL AND CSTL WTRS describes the area for which this FA forecast is valid PRECAUTIONARY STATEMENTS Between the communicationsproduct header and the body of the forecast are three precautionary statements See example FA on page 417 The first statement in the example SEE AIRMET SIERRA FOR IFR CONDS AND MTN OBSCN is included to alert users that IFR conditions andor mountain obscurations may be occurring or may be forecasted to occur in a portion of the FA area The user shall always check the latest AIRMET Sierra for the FA area The second statement in the example TS IlVlPLY SEV OR GTR TURB SEV ICE LLWS AND IFR CONDS is included as a reminder of the hazards existing in all thunderstorms Thus these thunderstormassociated hazards are not spelled out within the body of the FA The purpose of the third statement in the example NON MSL HGTS DENOTED BY AGL OR CIG is to alert the user that heights for the most part are mean sea level MSL All heights are in hundreds of feet For example BKN030 TOPS 100 HYR TRRN OBSCD means bases of the broken clouds are 3000 feet MSL with tops 10000 feet MSL Terrain above 3000 feet MSL will be obscured The tops of the clouds turbulence icing and freezing level heights are always MSL Heights AGL are noted in either of two ways 1 Ceilings by de nition are above ground Therefore the contraction CIG indicates above ground For example CIG BKNOVCO 15 means that ceilings are expected to be broken to overcast sky cover with bases at 1500 feet AGL 2 The contraction AGL means above ground level Therefore AGL SCT020 means scattered clouds with bases 2000 feet AGL 418 December 1999 Thus if the contraction AGL or CIG is not denoted height is automatically above MSL SYNOPSIS The synopsis is a brief summary of the location and movements of fronts pressure systems and other circulation features for an 18hour period References to low ceilings andor visibilities strong winds or any other phenomena the forecaster considers useful may also be included The following synopsis is taken from the example on page 417 SYNOPSISLOW PRES TROF 10Z OKTX PNHDL AREA FCST MOV EWD INTO CNTRLSWRN OK BY 04Z WRMFNT 10Z CNTRL OKSRN ARNRN MS FCST LIFT NWD INTO NERN OK NRN AR XTRM NRN MS BY 04Z This paragraph states that a low pressure trough at 10Z was over the Oklahoma OK Texas TX panhandle area The area is forecasted to move eastward into centralsouthwestern OK by 04Z At 10Z a warm front was located from central OK to southern Arkansas AR to northern Mississippi MS This warm front is forecasted to lift into northeastern OK northern AR to extreme northern MS by 04Z VFR CLOUDS AND WEATHER VFR CLDSWX This section contains a 12hour speci c forecast followed by a 6hour categorical outlook giving a total forecast period of 18 hours and it is usually several paragraphs in length The breakdown may be by states or by wellknown geographical areas See Figure 411 The speci c forecast section gives a general description of clouds and weather which cover an area greater than 3000 square miles and are signi cant to VFR ight operations Surface visibility and obstructions to vision are included when the forecast visibility is 3 to 5 statute miles Precipitation thunderstorms and sustained winds of 20 knots or more will always be included when forecasted The conditional term OCNL occasional is used to describe clouds and visibilities that may affect VFR ights It is used when there is a greater than 50 probability of a phenomenon occurring but for less than 12 the forecast period The areal coverage terms ISOL isolated WDLY SCT widely scattered SCT or AREAS scattered and NMRS or WDSPRD numerous or widespread are used to indicate the area coverage of thunderstorms or showers The term ISOL may also be used to describe areas of ceilings or visibilities that are expected to affect areas less than 3000 square miles Table 41 de nes the areal coverage terms Table 4 1 Areal Coverage of Showers and Thunderstorms Terms Coverage Isolated ISOL Single cells no percentage Widely scattered Less than 2500 of area affected WDLY SCT Scattered or Areas 25 to 5400 of area affected SCT 0r AREAS Numerous or Widespread 5500 or more of area affected NMRS 0r WDSPRD 419 December 1999 Example from the FA on page 417 CSTL WTRS LA MS AL WTRSSCT025 SCTBKN080 TOPS 150 ISOL TSRA CB TOPS FL350 OTLKVFR TX WTRSSCT CI OCNL SCT030 OTLKVFR This part of the VFR cloudsweather section is the forecast for the coastal waters of Louisiana LA Mississippi MS Alabama AL and Texas TX For the coastal waters of LA MS and AL the base of the scattered layer is 2500 feet MSL The second layer is scattered to broken at 8000 feet MSL with tops at 15000 feet MSL Also during this time isolated ISOL thunderstorms with light rain showers are expected with the tops of the thunderstorms CB at ight level FL 350 FL is used only for altitudes 18000 feet MSL and higher The visibility is expected to be greater than 6 statute miles and winds less than 20 knots both by omission The weather conditions along the TX coastal waters are expected to be scattered cirrus with occasional OCNL scattered layers at 3000 feet MSL A categorical outlook identi ed by OTLK is included for each area breakdown A categorical outlook of instrument ight rules IFR and marginal VFR MVFR can be due to ceilings only CIG restriction to visibility only TSRA FG etc or a combination of both In the example the coastal areas have outlooks of VFR conditions The statement OTLK VFR BCMG MVFR CIG F AFT 09Z means the weather is expected to be VFR becoming MVFR due to low ceiling and visibilities restricted by fog after 0900Z WND is included in the outlook if winds sustained or gusty are expected to be 20 knots or greater Hazardous weather ie IFR icing and turbulence conditions is n0t included in the FA but are included in the Inflight Aviation Weather Advisories see page 4 23 AMENDED AVIATION AREA FORECAST Amendments to the FA are issued as needed An amended FA is identi ed by AMD that is located on the first line after the date and time The entire FA is transmitted again with the word UPDT after the state to indicated what sections have been amendedupdated FAs are also amended and updated by in ight aviation weather advisories AIRMETs SIGMETs and Convective SIGMETs A corrected FA is identi ed by COR and a delayed FA is identi ed by RTD which are located in the rst line after the time and date IZ3917 AVIATION AREA FORECASTS 1quot O I Iquot 808 CHI quot osm 1 SLC HICAG F0 SAL LAKE c i A t FHA cusco j w t i g I L39 DFW MI DALLAS W0 TH 39 a squot L v X 1 39 39 x x Figure 45 FA Locations Contiguous United States 6661 Jeqweoeo December 1999 AREA FORECAST LOCA39I10NS HAWAII mm A5 FA humans rHawuu December 1999 INFLIGHT AVIATION WEATHER ADVISORIES In ight Aviation Weather Advisories are forecasts to advise en route aircraft of development of potentially hazardous weather All in ight aviation weather advisories in the conterminous US are issued by the Aviation Weather Center AWC in Kansas City Missouri The WFO in Honolulu issues advisories for the Hawaiian islands In Alaska the Alaska Aviation Weather Unit AAWU issues in ight aviation weather advisories All heights are referenced MSL except in the case of ceilings CIG which indicate AGL There are three types of in ight aviation weather advisories the Signi cant Meteorological Information SIGMET the Airman s Meteorological Information AIRMET and Convective SIGMET All of these advisories use the same location identi ers either VORs airports or wellknown geographic areas to describe the hazardous weather areas see Figures 411 and 412 on pages 445 and 446 SIGMET WSAIRMET WA SIGMETsAIRMETs are issued corresponding to the FA areas see Figures 45 and 46 The maximum forecast period is 4 hours for SIGMETs and 6 hours for AIRMETs Both advisories are considered widespread because they must be either affecting or be forecasted to affect an area of at least 3000 square miles at any one time However if the total area to be affected during the forecast period is very large it could be that in actuality only a small portion of this total area would be affected at any one time SIGMET WS A SIGMET advises of nonconvective weather that is potentially hazardous to all aircraft SIGMETs are unscheduled products that are valid for 4 hours However conditions that are associated with hurricanes are valid for 6 hours Unscheduled updates and corrections are issued as necessary In the conterminous US SIGMETs are issued when the following phenomena occur or are expected to occur 1 Severe icing not associated with thunderstorms 2 Severe or extreme turbulence or clear air turbulence CAT not associated with thunderstorms 3 Dust storms or sandstorms lowering surface or in ight visibilities to below 3 miles 4 Volcanic ash In Alaska and Hawaii SIGMETs are also issued for l Tornadoes 2 Lines of thunderstorms 3 Embedded thunderstorms 4 Hail greater than or equal to 3 inch in diameter SIGMETs are identi ed by an alphabetic designator from November through Yankee excluding Sierra and Tango Sierra Tango and Zulu are reserved for AIRMETs The first issuance of a SIGMET will be labeled as UWS Urgent Weather SIGMET Subsequent issuances are at the forecaster s discretion Issuance for the same phenomenon will be sequentially numbered using the original designator until the phenomenon ends For example the rst issuance in the Chicago CHI FA area for phenomenon moving from the Salt Lake City SLC FA area will be SIGMET Papa 3 if the previous two issuances Papa l and Papa 2 had been in the SLC FA area Note that no two different phenomena across the country can have the same alphabetic designator at the same time December 1999 Example of a SIGMET BOSR WS 050600 SIGMET ROMEO 2 VALID UNTIL 051000 ME NH VT FROM CAR TO YSJ TO CON TO MPV TO CAR MOD TO OCNL SEV TURB BLW 080 EXP DUE TO STG NWLY FLOW CONDS CONTG BYD 1000Z International SIGMET Some NWS offices have been designated by the ICAO as Meteorological Watch Of ces MWOs These offices are responsible for issuing International SIGMETs for designated areas that include Alaska Hawaii portions of the Atlantic and Paci c Oceans and the Gulf of Mexico The of ces which issue International SIGMETs are the Alaskan Aviation Weather Unit in Anchorage Alaska AKthe Tropical Prediction Center in Miami Florida FL the WFO in Honolulu Hawaii HI the Aviation Weather Center in Kansas City MO and the WFO on Guam Island in the Pacific Ocean These SIGMETs are considered widespread because they must be either affecting or be forecasted to affect an area of at least 3000 square miles at any one time The Intemational SIGMET is issued for 12 hours for volcanic ash events 6 hours for hurricanes and tropical storms and 4 hours for all other events Like the domestic SIGMETs Intemational SIGMETs are also identi ed by an alphabetic designator from Alpha through Mike and are numbered sequentially until that weather phenomenon ends The criteria for an Intemational SIGMET are 1 Thunderstorms occurring in lines embedded in clouds or in large areas producing tornadoes or large hail Tropical cyclones Severe icing Severe or extreme turbulence Dust storms and sandstorms lowering visibilities to less than 3 miles Volcanic ash F P39 eENN Example of an International SIGMET ZCZC MIASIGAlL TTAA00 KNHC 121600 KZNY SIGMET LIMA 5 VALID 121600 122000 UTC KNHC ACT TS OBS BY SATELLITE WI AREA BOUNDED BY 30N69W 31N646W 264N664W 275N694W 30N69W CB TOPS TO FL480 MOV ENE 15 KT INTSF AIRMET WA AIRMETs WAs are advisories of signi cant weather phenomena but describe conditions at intensities lower than those which require the issuance of SIGMETs AIRMETs are intended for dissemination to all pilots in the pre ight and en route phase of ight to enhance safety AIRMET Bulletins are issued on a scheduled basis every 6 hours beginning at 0145 UTC during Central Daylight Time and at 0245 UTC during Central Standard Time Unscheduled updates and corrections are issued as necessary Each AIRMET Bulletin contains any current AIRMETs in effect and an outlook for conditions expected after the AIRMET valid period AIRMETs contain details about IFR extensive mountain obscuration turbulence strong surface winds icing and freezing levels December 1999 There are three AIRMETs Sierra Tango and Zulu AIRMET Sierra describes IFR conditions andor extensive mountain obscurations AIRMET Tango describes moderate turbulence sustained surface winds of 30 knots or greater and or nonconvective lowlevel wind shear AIRMET Zulu describes moderate icing and provides freezing level heights After the rst issuance each day scheduled or unscheduled bulletins are numbered sequentially for easier identi cation Example of AIRMET Sierra issued for the Chicago FA area CPHS WA 121345 AIRMET SIERRA UPDT 3 FOR IFR AND MTN OBSCN VALID UNTIL 122000 AIRMET IFRSD NE MN IA MO WI LMMI IL IN KY FROM 70NW RAP TO 50W RWF TO 50W MSN TO GRB TO MBS TO FWA TO CVG TO HNN TO TRI TO ARG TO 40SSW BRL TO OMA TO BFF TO 70NW RAP OCNL CIG BLW 010VIS BLW 3SM FGBR CONDS ENDG 15Z17Z AIRMET MTN OBSCNKY TN FROM HNN TO TRI TO CHA TO LOZ TO HNN MTNS OCNL OBSC CLDSPCPNBR CONDS ENDG TN PTN AREA 18Z 20ZCONTG KY BYD 20ZENDG 02Z Example of AIRMET Tango issued for the Salt Lake City FA area SLCT WA 121345 AIRMET TANGO UPDT 2 FOR TURB VALID UNTIL 122000 AIRMET TURBNV UT CO AZ NM FROM LKV TO CHE TO ELP TO 60S TUS TO YUM TO EED TO RNO TO LKV OCNL MOD TURB BLW FL180 DUE TO MOD SWLYWLY WNDS CONDS CONTG BYD 20Z THRU 02Z AIRMET TURBNV WA OR CA CSTL WTRS FROM BLI TO REO TO BTY TO DAG TO SBA TO 120W FOT TO 120W TOU TO BLI OCNL MOD TURB BTWN FL180 AND FL400 DUE TO WNDSHR ASSOCD WITH JTSTR CONDS CONTG BYD 20Z THRU 02Z Example of AIRMET Zulu issued for the San Francisco FA area SFOZ WA 121345 AIRMET ZULU UPDT 2 FOR ICE AND FRZLVL VALID UNTIL 122000 AIRMET ICEWA OR ID MT NV UT FROM YQL TO SLC TO WMC TO LKV TO PDT TO YDC TO YQL LGT OCNL MOD RIMEMXD ICGICIP BTWN FRZLVL AND FL220 FRZLVL 080120 CONDS CONTG BYD 20Z THRU 02Z AIRMET ICEWA OR FROM YDC TO PDT TO LKV TO 80W MFR TO ONP TO TOU TO YDC LGT OCNL MOD RIMEMXD ICGICIP BTWN FRZLVL AND FL180 FRZLVL 060080 CONDS CONTG BYD 20Z THRU 02Z FRZLVLWA060 CSTLN SLPG 100 XTRM E OR060070 CASCDS WWD 070095 RMNDR NRN CA060100 N OF A 30N FOT40N RNO LN SLPG 100110 RMNDR 425 December 1999 CONVECTIVE SIGMET WST Convective SIGMETs are issued in the conterminous US for any of the following 1 Severe thunderstorm due to a surface winds greater than or equal to 50 knots b hail at the surface greater than or equal to 3 inches in diameter c tornadoes 2 Embedded thunderstorms 3 A line of thunderstorms 4 Thunderstorms producing precipitation greater than or equal to heavy precipitation affecting 40 or more of an area at least 3000 square miles Any convective SIGMET implies severe or greater turbulence severe icing and lowlevel wind shear A convective SIGMET may be issued for any convective situation that the forecaster feels is hazardous to all categories of aircraft Convective SIGMET bulletins are issued for the western W central C and eastern E United States Convective SIGMETs are not issued for Alaska or Hawaii The areas are separated at 87 and 107 degrees west longitude with sufficient overlap to cover most cases when the phenomenon crosses the boundaries Bulletins are issued hourly at H55 Special bulletins are issued at any time as required and updated at H55 If no criteria meeting convective SIGMET requirements are observed or forecasted the message CONVECTIVE SIGMET NONE will be issued for each area at H55 Individual convective SIGMETs for each area W C E are numbered sequentially from number one each day beginning at 00Z A convective SIGMET for a continuing phenomenon will be reissued every hour at H55 with a new number The text of the bulletin consists of either an observation and a forecast or just a forecast The forecast is valid for up to 2 hours Example of a convective SIGMET MKCC WST 251655 CONVECTIVE SIGMET 54C VALID UNTIL 1855Z WI IL FROM 30E MSN40ESE DBQ DMSHG LINE TS 15 NM WIDE MOV FROM 30025KT TOPS TO FL450 WIND GUSTS TO 50 KT POSS CONVECTIVE SIGMET 55C VALID UNTIL 1855Z WI IA FROM 30NNW MSN30SSE MCW DVLPG LINE TS 10 NM WIDE MOV FROM 30015KT TOPS TO FL300 CONVECTIVE SIGMET 56C VALID UNTIL 1855Z MT ND SD MN IA MI LINE TS 15 NM WIDE MOV FROM 27020KT TOPS TO FL380 OUTLOOK VALID 151855252255 FROM 60NW ISNINLTVCSBNBRLFSDBIL60NW ISN December 1999 IR STLT IMGRY SHOWS CNVTV CLD TOP TEMPS OVER SRN WI HAVE BEEN WARMING STEADILY INDCG A WKNG TREND TIHS ALSO REFLECTED BY LTST RADAR AND LTNG DATA WKNG TREND OF PRESENT LN MAY CONT HWVR NEW DVLPMT IS PSBL ALG OUTFLOW BDRY ANDOR OVR NE IASW WI BHD CURRENT ACT A SCND TS IS CONTG TO MOV EWD THRU ERN MT WITH NEW DVLPMT OCRG OVR CNTRL ND MT ACT IS MOVG TWD MORE FVRBL AMS OVR THE WRN DAKS WHERE DWPTS ARE IN THE UPR 60S WITH LIFTED INDEX VALUES TO MS 6 TS EXPD TO INCR IN COVERAGE AND INTSTY DURG AFTN HRS WST ISSUANCES EXPD TO BE RQRD THRUT AF TN HRS WITH INCRG PTNTL FOR STGR CELLS TO CONTAIN LRG HAIL AND PSBLY DMGG SFC WNDS ALASKA GULF OF MEXICO AND INTERNATIONAL AREA FORECASTS gFAs ALASKA AREA FORECAST FA The Alaska Aviation Weather Unit in Anchorage Alaska produces the FA for the entire state of Alaska The Alaska FA combines the FA SIGMETs and AIRMETs into one product Each FA contains a regional synopsis l2hour geographic speci c forecasts and an 18hour outlook for each geographic area Forecast weather elements are sky condition cloud height mountain obscuration visibility weather andor obstructions to visibility strong surface winds direction and speed icing freezing level and mountain pass conditions Hazards and ight precautions including AIRMETs and SIGMETs may be found in their respective geographic area AIRMETs and SIGMETs are also issued as separate products Partial example of Alaska FA JNUH FA 191445 EASTERN GULF COAST AND SE AK AIRMET VALID UNTIL 230300 TS IIVIPLY POSSIBLE SEV OR GREATER TURB SEV ICE LLWS AND IFR CONDS NON MSL HEIGHTS NOTED BY AGL OR CIG SYNOPSIS VALID UNTIL 231500 990 MB LOW VCY PACV DRFTG E AND WKN CDFNT S FM LOW BCMG STNR AND WK ICY BAY SWD BY 15Z E PACIFIC LOW S 50N MOV N TO 975 MB CNTR 50 SM W PASI AT 15Z WI OCFNT SWD LYNN CANAL AND GLACIER BAY TB VALID UNTIL 230900 CLOUDSWX AIRMET MT OBSC TEMPO MT OBSC INCLDS NC SCT030 SCTBKN050 BKN100 TOP 160 TEMPO IH LYRS TOP FL250 TEMPO BKN030 ISOL RA SFC WND S 15 KT G25 KT LYNN CANAL OTLK VALID 230900240300 VFR RA 18Z MVFR CIG RA PASSES WIHTE AND CIHLKOOT MVFR CIG RASN TURB LYNN CANAL ISOL MOD TURB BLW 060 ELSWNIL SIG ICE AND FZLVL TEMPO LGT RIME ICEIC 050120 FZLVL 030 427 December 1999 ALASKA AREA FORECAST SECTORS Figure 47 Alaska Area Forecast Sectors 428 December 1999 GULF OF MEXICO AREA FORECAST A specialized FA for the Gulf of Mexico is issued by the Tropical Prediction Center in Miami Florida The product combines the FA in ight aViation weather advisories and marine precautions This product is intended to support both offshore heliport and general aViation operations The Gulf of Mexico FA focuses on an area which includes the coastal plains and coastal waters from Apalachicola Florida to Brownsville Texas and the offshore waters of the Gulf of Mexico in an area west of 85W longitude and north of 27N latitude Each section of the FA describes the weather conditions expecting to impact the area and will include the descriptor none if no significant weather is forecast to occur Amendments to this FA are issued the same as amendments to the domestic FAs Partial example of Gulf of Mexico FA FAGXOl KNHC 151030 151100Z 152300Z OTLK152300Z 161100Z AMDT NOT AVBL 0200Z1100Z TROPICAL ANALYSIS AND FORECAST BRANCH TROPICAL PREDICTION CENTER MIAMI FLORIDA GLFMEX N OF 27N W OF 85W CSTL PLAINS CSTL WTRS AQQBRO HGTS MSL UNLESS NOTED TS IlVlPLY POSS SEV OR GTR TURB SEV ICE LOW LVL WS AND STG SFC WND IHGH WAVES CIG BLW 010 AND VIS BLW 3SM 01 SYNS WK SFC TROUGH FM 31N84W TO 26N88W AT llZ DRIFTING E THROUGH 23Z WK IHGH PRES ACRS RMNDER GLFMEX THRU FCST AND OTLK PD 02 FLT PRCTNS NONE 03 MARINE PRCTNS NONE 04 SGFNT CLDWX CSTL PLAINS CSTL WTRS BROLCH AND OFSHR WTRS W OF 94W FEW040 OTLK VFR CSTL PLAINS LCHAQQ FEW015 OCNL VIS 35SM BR AFT 14Z SCT100 AFT 19Z SCTBKN020030 BKNSCT070090 WIDELY SCT TSRAISOL TSRA 05 ICE AND FZ LEVEL BLW 120 NONE FZ LEVEL ABV 120 06 TURB BLW 120 NONE 429 December 1999 07 WND BLW 120 CSTL PLAINS CSTL WTRS LCHGPT AND OFSHR WTRS 94W89W SFC120 NEE 1015 KT OTLK NOSIG 08 WAVES CSTL WTRS BROAQQ 12 FT OTLK NOSIG NNNN INTERNATIONAL AREA FORECASTS FAs from the surface to 25000 feet are also prepared in international format for areas in the Atlantic Ocean Caribbean Sea and the Gulf of Mexico Moreover signi cant weather forecasts for 25000 feet to 60000 feet are prepared in chart form and in international text format for the Northern and Western hemispheres Example of an International FA from the surface to FL250 FANT2 KWBC 091600 091800Z TO 100600Z ATLANTIC OCEAN WEST OF A LINE FROM 40N 67W TO 32N 63W SFC TO FL250 SYNOPSIS RIDGE OVER AREA MOVING TO EAST FRONTAL SYSTEM MOVING OFF COAST BY 06Z SIGNIFICANT CLDSWX N OF 34N AND W OF 71W PATCHES OVC005015 TOP 030040 OTHERWISE BKNOVC015025 BKNOVC200240 BY 06Z INCREASING IIVIC IN SHRATS SPREADING ACROSS AREA FROM WEST TS TOPS ABOVE 240 S OF 34N AND W OF 75W SCTBKN 015250 BY 06Z INCREASING IMC IN SHRATS SPREADING ACROSS AREA FROM WEST TS TOPS ABOVE 240 ELSEWHERE CLR OCNL SCTO 15025 BY 06Z INCREASING BKN080100 ICE FZ LVL 080090 N SLOPING TO 120130 S MOD IN SHRA SEV IN TS TURB MOD IN SHRA SEV IN TS OUTLOOK 100600Z TO 101800Z FRONT CONTINUING SLOWLY EWD INCREASING IIVIC IN SHRATS SPREADNG E OVER AREA SHRATS ENDING SW PORTION AFTER FRONTAL PASSAGE 430 December 1999 Example of international signi cant weather forecast for FL250 to FL600 FAPAl KWBC 141610 SIG WX PROG FL250FL600 VALID 150600Z ISOL EMBD CB TOPS 400 NE OF 11N173W 14N166W 11N164W 01N174W ISOL EMBD CB TOPS 400 07N158W 08N137W11N137W 12N158W 07N158W ISOL EMBD CB TOPS 400 19N157W 32N143W 22N162W 15N162W MDT OR GRTR TURB AND ICG VCNTY ALL CBS MDT TURB 310410 19N145W 25N144W19N163W 15N162W 19N145W The groups of numbers and letters are the boundary points of the areas in latitude and longitude For example 11N173W is latitude 11 degrees north and longitude 173 degrees west TRAN SCRIBED WEATHER BROADCAST gTWEB TEXT PRODUCTS NWS offices prepare transcribed weather broadcast TWEB text products for the contiguous US including synopsis and forecast for more than 200 routes and local vicinities See Figure 48 Not all NWS forecast of ces issue all three of these products These products may be used in the Telephone Information Brie ng Service TIBS Pilot s Automatic Telephone Weather Answering Service PATWAS LowMedium Frequency LMF and VHF omnidirectional radio range VOR facilities as described in Section 1 TWEB products are valid for 12 hours and are issued 4 times a day at 0200Z 0800Z 1400Z and 2000Z A TWEB route forecast or vicinity forecast will not be issued if the TAF for that airport has not been issued A NIL TWEB will be issued instead A TWEB route forecast is for a 50nauticalmile wide corridor along a line connecting the end points of the route A TWEB local vicinity forecast covers an area with a radius of 50 nautical miles The route and vicinity forecasts describe specific information on sustained surface winds 25 knots or greater visibility weather and obscuration to vision sky conditions coverage and ceilingcloud heights mountain obscurement and nonconvective lowlevel wind shear vaisibility of 6SM or less is forecast obstructions to vision andor weather will be included Thunderstorms and volcanic ash will always be included regardless of the visibility Cloud bases can be described either in MSL or AGL CIGS or BASES It depends on which statement is used ALL HGTS MSL XCP CIGS or ALL HGTS AGL XCP TOPS Use of AGL CIGS and BASES should be limited to cloud bases within 4000 feet of the ground Cloud tops referenced to MSL should also be forecasted following the sky cover when expected to be below 15000 MSL using the sky cover contractions FEW SCT or BKN Nonconvective lowlevel wind shear will be included when the TAF for the airport involved has issued a nonconvective lowlevel wind shear forecast Expected areas of icing and turbulence will not be included Example of TWEB route forecast 249 TWEB 251402 KISNKMOTKGFK ALL HGTS AGL XCP TOPS KISN50NM E KISN TIL 00Z P6SM SKC AFT 00Z P6SM SCT050 LCL P6SM TSRA BKN050 50NM E KISNKDVL TIL 20Z P6SM SCT070 AFT 20Z P6SM SCT070 LCL SFC WNDS VRB35G45KT 35 SM TSRA CIGS OVC030040 KDVLKGFK TIL 16Z P6SM SCTBKN020 AREAS 35SM BR AFT 16Z P6SM SCT040 431 December 1999 Explanation of route forecast 249 route number TWEB TWEB route forecast 25 twenty fth day of the month 1402 valid 14Z on the twenty fth to 02Z on the twentysixth 12 hours KISNKMOTKGFK route Williston North Dakota ND to Minot ND to Grand Forks ND Remainder of the message explained All heights AGL except cloud tops KISN50NM E KISN until 00Z visibility greater than 6SM with clear skies After 00Z visibility greater than 6SM with scattered clouds at 5000 feet AGL Local areas of visibility greater than 6SM thunderstorm with light rain showers and broken clouds at 5000 feet AGL 50 NM E KISNKDVL Devil s Lake ND until 20Z visibility greater than 6SM scattered clouds at 7000 feet AGL After 20Z visibility greater than 6SM scattered clouds at 7000 feet AGL local surface winds variable at 35 gusting to 45 knots visibility 3 5SM thunderstorm with moderate rain showers overcast ceilings 30004000 feet AGL KDVLKGFK until 16Z visibility greater than 6SM scattered to broken clouds at 2000 feet AGL areas of visibility 3 5SM with mist After 16Z visibility greater than 6SM scattered clouds at 4000 feet AGL An example of TWEB vicinity forecast 431 TWEB 021402 LAX BASIN ALL HGTS MSL XCP CIGS TIL 18Z P6SM XCP 3SM BR VLYS BKN02018Z22Z P6SM SCT020 SCTBKN100 AFT 22Z P6SM SKC Explanation of vicinity forecast 431 TWEB vicinity number TWEB TWEB forecast 02 second day of the month 1402 valid 14Z on the second to 02Z on the third 12 hours LAX BASIN The weather conditions in the Los Angeles basin until 18Z visibility greater than 6SM except 3SM due to mist in the valleys and broken clouds at 2000 feet MSL Between 18Z and 22Z visibility greater than 6SM and scattered clouds at 2000 feet AGL also scattered to broken clouds at 10000 feet MSL After 22Z visibility greater than 6SM and sky clear A TWEB synopsis forecast is a brief description of the weather systems affecting the route during the forecast valid period The synopsis describes movement of pressure systems movement of fronts upper air disturbances or air ow An example of a TWEB synopsis BIS SYNS 250820 LO PRES TROF MVG ACRS ND TDA AND TNGT IH PRES MVG SEWD FM CANADA INTO NWRN ND BY TNGT AND OVR MST OF ND BY WED MRNG Explanation of synopsis BIS Bismarck ND WFO issuing the synopsis and route forecast SYNS Synopsis for the area covered by the route forecast 25 twenty fth day of the month 0820 Valid from 08Z on the twenty fth to 20Z on the twenty fth 12 hours The remainder of message explained Low pressure trough moving across North Dakota today and tonight High pressure moving southeastward from Canada into northwestern North Dakota by tonight and over most of North Dakota by Wednesday morning 432 December 1999 An example of another TWEB synopsis CYS SYNS 101402 STG UPSLP WNDS OVR WY TIL 01Z WITH WDSPRD IFR CONDS IN LGT SN AND BLOWING SN CONDS WL IPV FM N TO S ACRS WY AFT 01Z WITH DCRG CLDS Explanation of synopsis CYS Cheyenne WY WFO issuing the synopsis and route forecast SYNS Synopsis for the area covered by the route forecast 10 tenth day of the month 1402 Valid from 14Z on the tenth to 02Z on the eleventh 12 hours The remainder of the message explained Strong upslope winds over Wyoming until 01Z with widespread IFR conditions in light snow and blowing snow Conditions will improve from north to south across Wyoming after 01Z with decreasing clouds 433 December 1999 92 250m mm H m 25m Cma azv 335 23 mum and Inon 3020quot a2lt Eve 0 mnowau 2305 150 201 DZMUm J XEOEm Z MFDOE mm gtgt g 30 25 Eng zg 205 I gtm2v 102 Owns awn v awe I Oi 4 34 December 1999 WINDS AND TEMPERATURES ALOFT FORECAST gFDL Winds and temperatures aloft are forecasted for specific locations in the contiguous US as shown in Figure 49 The FD forecasts are also prepared for a network of locations in Alaska and Hawaii as shown in Figure 410 Forecasts are made twice daily based on the 00Z and 12Z radiosonde data for use during specific time intervals Below is a sample FD message containing a heading and two FD locations The heading always includes the time during which the FD may be used 05000900Z in the example and a notation TEMPS NEG ABV 24000 Since temperatures above 24000 feet are always negative the minus sign is omitted Example of FD report DATA BASED ON 010000Z VALID 010600Z FOR USE 05000900Z TEMPS NEG ABV 24000 FT 3000 6000 9000 12000 18000 24000 30000 34000 39000 MKC 2426 272609 282614 293021 274432 275141 275550 276050 731960 ABQ 191215 191407 191706 182017 172132 171942 192054 Explanation of FD The data are based on the radiosonde information from the 1st day of the month at 00Z The second line describes the valid time In this example the valid time is the 1st at 06Z for use on the 1st between 05 09Z Temperatures are negative above 24000 feet The line labeled FT indicates the levels of the wind and temperature data Through 12000 feet the levels are true altitude From 18000 feet and above the levels are pressure altitude The 45000foot and 53000foot levels are also available The pilot may request these levels from the FSS briefer A sixdigit group shows wind direction in reference to true north wind speed in knots and temperature in degrees Celsius Note the Kansas City MO MKC forecast for 3000 feet The group 2426 means the wind is from 240 degrees at 26 knots The first two digits give direction in tens of degrees and the second two digits are the wind speed in knots In the MKC forecast the coded group for 9000 feet is 282614 The wind is from 280 degrees at 26 knots and the temperature is negative 14 degrees Celsius Note in the Albuquerque ABQ 3000 and 6000foot examples that the wind group is omitted No winds are forecasted within 1500 feet of station elevation Also no temperatures are forecasted for any level within 2500 feet of station elevation See MKC 3000 example If a wind direction is coded between 51 and 86 the wind speed is 100 knots or greater For example the MKC forecast for 39000 feet is 731960 To decode this subtract 50 from the wind direction and add 100 knots to the wind speed Thus the wind direction is from 230 degrees 735023 and the speed is 119 knots 10019119 The temperature is minus 60 degrees Celsius Ifthe wind speed is forecasted to be 200 knots or greater the wind group is coded as 99 knots For example 7799 is decoded as 270 degrees at 199 knots or greater When the forecast speed is less than 5 knots the coded group is 9900 and read LIGHT AND VARIABLE Examples of decoding FDs Coded Decoded 990000 Wind light and variable temperature 0 degrees Celsius 2707 270 degrees at 7 knots 850552 350 degrees 855035 at 105 knots 10005105 temperature 52 degrees Celsius 9917 FORECAST WINDS AND TEMPERATURES ALOFT NETWORK Figure 49 FD Locations for Contiguous United States 6661 Jeqweoeo 4H SAB 39SNP ADK Asa n w a f 3 u C3003 A4 SAE39 Z EAD39 ALASKA LOCATIONS a lt2 R1 HNL HAWAII LOCATIONS Figure 410 FD Locations for Alaska and Hawaii December 1999 SAC December 1999 CENTER WEATHER SERVICE UNIT CWS PRODUCTS Center Weather Service Unit CWSU products are issued by the CWSU meteorologists located in the Air Route Traf c Control Centers ARTCCs Coordination between the CWSU meteorologist and other NWS facilities is extremely important since both can address the same event If time permits coordination should take place before the CWSU meteorologist issues a product METEOROLOGICAL IMPACT STATEMENT MIS A Meteorological Impact Statement MIS is an unscheduled ow control and ight operations planning forecast The MIS can be valid between 2 to 12 hours after issuance This enables the impact of expected weather conditions to be included in air traf c control decisions in the near future The MIS will be issued when the following three conditions are met If any one of the following conditions occur are forecasted to occur and if previously forecasted are no longer expected to occur convective SIGMET criteria moderate or greater icing and or turbulence heavy or freezing precipitation low IFR conditions surface winds gusts 30 knots or greater lowlevel wind shear within 2000 feet of the surface volcanic ash dust or sandstorrn If the impact occurs on air traf c ow within the ARTCC area of responsibility If the forecast lead time the time between issuance and onset of a phenomenon in the forecaster s judgment is suf cient to make issuance of a Center Weather Advisory CWA unnecessary whorl9w WP Example of a MIS ZOA MIS 01 VALID 041415041900 FOR ATC PLANNING PURPOSES ONLY FOR SFO BAY AREA DNS BRFG WITH CIG BLO 005 AND VIS OCNL BLO 1SM TIL 19Z This MIS from the Fremont California CA ARTCC is the rst issuance of the day It was issued at 1415Z on the fourth and is valid until l900Z on the fourth This forecast is for the San Francisco Bay area The forecast is of dense fogmist with ceilings below 500 feet and visibilities occasionally below 1SM until 19Z Example ZOA MIS 02 VALID 041650 FOR ATC PLANNING PURPOSES ONLY FOR SFO BAY AREA CANCEL ZOA MIS 01 DNS BRFG CONDS HAVE IPVD ERYR THAN FCST This MIS is from the Fremont CA ARTCC and cancels the previously issued MIS Speci cally it states dense fogmist conditions have improved earlier than forecasted December 1999 Example ZID MIS 03 VALID 041200042330 FOR ATC PLANNING PURPOSES ONLY FROM IND TO CIVIH TO LOZ TO EVV TO IND FRQ MOD TURBC FL310390 DUE TO JTSTR CONDS DMSHG IN INTSTY AFT 21Z This MIS from the Indianapolis Indiana IN ARTCC was issued at l200Z on the fourth and valid until the fourth at 2330Z This forecast describes an area from Indianapolis IN to Columbus Ohio OH to London Kentucky KY to Evansville IN and back to Indianapolis IN The MIS describes frequent moderate turbulence between ight levels 310390 caused by the jet stream Conditions will diminish in intensity after 2lZ CENTER WEATHER ADVISORY CWA A Center Weather Advisory CWA is an aviation warning for use by air crews to anticipate and avoid adverse weather conditions in the en route and terminal environments The CWA is not a ight planning product instead it re ects current conditions expected at the time of issuance and or is a shortrange forecast for conditions expected to begin within 2 hours of issuance CWAs are valid for a maximum of 2 hours If conditions are expected to continue beyond the 2hour valid period a statement will be included in the CWA A CWA may be issued for the following three situations 1 As a supplement to an existing in ight aviation weather advisory for the purpose of improving or updating the definition of the phenomenon in terms of location movement extent or intensity relevant to the ARTCC area of responsibility This is important for the following reason A SIGMET for severe turbulence was issued by AWC and the outline covered the entire ARTCC area for the total 4hour valid time period However the forecaster may issue a CWA covering only a relatively small portion of the ARTCC area at any one time during the 4hour period 2 When an in ight aviation weather advisory has not yet been issued but conditions meet the criteria based on current pilot reports and the information must be disseminated sooner than the AWC can issue the in ight aviation weather advisory In this case of an impending SIGMET the CWA will be issued as urgent UCWA to allow the fastest possible dissemination 3 When in ight aviation weather advisory criteria are not met but conditions are or will shortly be adversely affecting the safe ow of air traffic within the ARTCC area of responsibility Example of a CWA ZMEl CWA 081300 ZME CWA 101 VALID UNTIL 081500 FROM MEM TO JAN TO LIT TO MEM AREA SCT VIP 56 INTENSEEXTREME TS MOV FROM 26025KT TOPS TO FL450 This CWA was issued by the Memphis Tennessee TN ARTCC The 1 after the ZME in the first line denotes this CWA has been issued for the rst weather phenomenon to occur for the day It was written on the eighth at l300Z The 101 in the second line denotes the phenomenon number again 1 and the issuance number 01 for this phenomenon The CWA is until the eighth at 1500Z The area is bounded from Memphis TN to Jackson MS to Little Rock AR and back to Memphis TN Within the CWA is an area with scattered VIP 56 intenseextreme thunderstorms moving from 260 degrees at 25 knots Tops of the thunderstorms are at FL450 December 1999 HURRICANE ADVISORY gWHg When a hurricane threatens a coastline but is located at least 300NM offshore a Hurricane Advisory WH is issued to alert aviation interests The advisory gives the location of the storm center its expected movement and the maximum winds in and near the storm center It does not contain details of associated weather as speci c ceilings visibilities weather and hazards that are found in the FAs TAFs and in ight aviation weather advisories Example of a WH ZCZC MIATCPAT4 TTAA00 KNHC 190841 BULLETIN HURRICANE DANNY ADVISORY NUMBER 13 NATIONAL WEATHER SERVICE MIAMI FL 4 AM CDT SAT JUL 19 1997 DANN Y STILL MOVING LITTLE AN Y NORTHWARD DRIFT WOULD BRING THE CENTER ONSHORE HURRICANE WARNINGS ARE IN EFFECT FROM GULFPORT MISSISSIPPI TO APALACIHCOLA FLORIDA SMALL CRAFT SOUTHWEST OF GULFPORT SHOULD REMAIN IN PORT UNTIL WINDS AND SEAS SUBSIDE AT 4 AM CDT 0900Z THE CENTER OF HURRICANE DANNY WAS LOCATED BY NATIONAL WEATHER SERVICE RADAR AND RECONNAISSANCE AIRCRAFT NEAR LATITUDE 302 NORTH LONGITUDE 880 WEST VERY NEAR THE COAST ABOUT 25 MILES SOUTHSOUTHEAST OF MOBILE ALABAMA DANNY HAS MOVED LITTLE DURING THE PAST FEW HOURS WIHLE SOME ERRATIC MOTION CAN BE EXPECTED DURING THE NEXT FEW HOURS A GRADUAL TURN TOWARD THE NORTHEAST IS EXPECTED TODAY ON TIHS COURSE THE CENTER IS EXPECTED TO MAKE LANDFALL IN THE WARNING AREA TODAY HOWEVER ANY DEVIAITON TO THE NORTH OR THE TRACK WOULD BRING THE CENTER ONSHORE WITHIN THE WARNING AREA AT ANYTIME MAXHVIUM SUSTAINED WINDS ARE NEAR 75 MPH WITH IHGHER GUSTS SOME STRENGTHENING IS STILL POSSIBLE PRIOR TO LANDFALL DAUPHIN ISLAND RECENTLY REPORTED GUSTS TO 66 MPH AND THE PRESSURE DROPPED TO 989MB 2920 INCHES DANNY HAS A RELATIVELY SMALL WIND FIELD HURRICANE FORCE WINDS EXTEND OUTWARD UP TO 25 MPH FROM THE CENTER AND TROPICAL STORM FORCE WINDS EXTEND OUTWARD UP TO 70 MILES LATEST MINIMUM CENTRAL PRESSURE REPORTED BY A RECONNAISSAN CE AIRCRAFT WAS 986 MB2911 INCHES RADAR SHOWS RAIN BANDS AFFECTING THE AREA FROM SOUTHERN MISSISSIPPI TO THE FLORIDA PANHANDLE TOTALS OF 10 TO 20 INCHES LOCALLY IHGHER COULD OCCUR NEAR THE TRACK OF DANNY DURING THE NEXT FEW DAYS STORM SURGE FLOODING OF 4 TO 5 FEET ABOVE NORMAL TIDES IS POSSIBLE ALONG THE GULF COAST EAST OF THE CENTER 440 December 1999 Example of WH forecastadvisory ZCZC MIATCMAT4 TTAAOO KNHC 190845 HURRICANE DANNY FORECASTADVISORY NUMBER 13 NATIONAL WEATHER SERVICE MIAMI FL AL0497 0900Z SAT JUL 19 1997 HURRICANE WARNINGS ARE IN EFFECT FROM GULFPORT MISSISSIPPI TO APALACIHCOLA FLORIDA SMALL CRAFT SOUTHWEST OF GULFPORT SHOULD REMAIN IN PORT UNTIL THE WINDS AND SEAS SUBSIDE HURRICANE CENTER LOCATED NEAR 302 N 880 W AT 190900Z POSITION ACCURATE WITHIN 30 NM PRESENT MOVEMENT NEARLY STATIONARY ESTHVIATED MINIMUM CENTRAL PRESSURE 986 MB MAX SUSTAINED WINDS 65 KTS WITH GUSTS TO 80 KT 64KT 15NE 20SE 0SW ONW 50 KT 20NE 30SE 30SW ONW 34KT 30E 60SE 60SW 30NW 12FT SEAS 30NE 60SE 60SW 30NW ALL QUADRANT RADII IN NAUTICAL MILES FORECAST VALID 191800Z 302N 874W MAX WIND 70 KT GUSTS 85 KT 64 KT 20NE 20SE 20SW 20NW 50 KT 25NE 30SE 30SW 25NW 34 KT 30NE 75SE 75SW 30NW CON VECTIVE OUTLOOK AC1 A Convective Outlook AC is a national forecast of thunderstorms There are two forecasts Day 1 Convective Outlook first 24 hours and Day 2 Convective Outlook next 24 hours These forecasts describe areas in which there is a slight moderate or high risk of severe thunderstorms as well as areas of general nonsevere thunderstorms The severe thunderstorm criteria are Winds equal to or greater than 50 knots at the surface or hail equal to or greater than 3 inch in diameter at the surface or tornadoes The Refer to the Convective Outlook Chart Section 12 for risk de nitions Forecast reasoning is also included in all ACs Outlooks are produced by the Storm Prediction Center SPC located in Norman OK The times of issuance for Day 1 are 0600Z 1300Z 1630Z 2000Z and 0100Z The initial Day 2 issuance is at 0830Z during standard time and 0730Z during daylight time It is updated at 1730Z The AC is a ight planning tool used to avoid thunderstorms 441 December 1999 Example MKC AC 291435 CONVECTIVE OUTLOOK REF AF OS NMCGPH940 VALID 291500Z301200Z THERE IS A SLGT RISK OF SVR TSTMS TO THE RIGHT OF A LINE FROM 10 NE JAX 35 NNW AYS AGS 15 E SPA 30 NE CLT 25 N FAY 30 ESE EWN GEN TSTMS ARE FCST TO THE RIGHT OF A LINE FROM 55 ESE YUM 30 NE IGM 15 S CDC 30 SW U24 25 ESE ELY 40 W P38 DRA 50 SW DRA 50 NW NID SAC 30 E ACV 25 E ONP 40 E BLI SEVERE THUNDERSTORM FORECAST DISCUSSION SERN U S COOL FRONT CONTS SCNC BORDER VERY MOIST AND UNSTBL AMS ALONG AND S OF FRONT E OF APLCHNS WITH CAPES TO REACH TO 4000 JKG WITH AF TN HEATING ALTHOUGH WIND PROFILES ARE WKCOMB OF FRONTAL CNVGNC COUPLED WITH SEA BREEZE FRONT WILL INITIATE PULSE SVR TSTMS VCNTY AND S OF FRONT TIHS AF TNEVE PRIIVIARY SVR EVENTS WILL BE WET DOWNBURST TO PUSH SWD FROM CNTRL RCKYS EWD TO MID ATLC CST E OF APLCNS FRONT NOW LCTD VCNTY WND DMG GENERAL THUNDERSTORM FORECAST DISCUSSION GULF CST AREA INTO SRN PLNS SFC FNT CURRENTLY LOCATED FM THE CAROLINAS WWD INTO PARTS OF OK WL CONT TO SAG SLOWLY SWD ACRS THE SRN APLCNSLWR MS VLY THRU THE REMAINDER OF THE PD S OF THE BNDRYA VRY MOIST AMS RMNS IN PLACE AS DWPNTS ARE IN THE MID TO UPR 70S WIHLE SOME CLDNS IS PRESENT ACRS THE AREASUF HEATING SHOULD OCR TO ALLOW FOR MDT TO STG AMS DSTBLZN DURG THE LATE MRNGERY AFTN AS A RESULTSFC BASED CAPE VALUES SHOULD BE AOA 2000 JKG TIHS AFTN BNDRYS FM OVERNIGHT CNVTN AS WELL AS SEA BREEZE CIRCULATIONS SHOULD BE SUF TO INITIATE SCT TO NMRS TSTMS ACRS THE AREA MID TO UPR LVL FLOW IS RELATIVELY WKSO TIHS SUG ORGANIZED SVR TSTM ACTVTY IS NOT LIKELY SEVERE WEATHER WATCH BULLETIN S W W s and ALERT MESSAGES AWWs A Severe Weather Watch Bulletin WW de nes areas of possible severe thunderstorms or tornado activity The bulletins are issued by the SPC in Norman OK WWs are unscheduled and are issued as required A severe thunderstorm watch describes areas of expected severe thunderstorms Severe thunderstorm criteria are 3Ainch hail or larger and or wind gusts of 50 knots 58 mph or greater A tornado watch describes areas where the threat of tornadoes exists In order to alert the WFOs CWSUs FSSs and other users a preliminary noti cation of a watch called the Alert Severe Weather Watch bulletin AWW is sent before the WW WFOs know this product as a SAW 442 December 1999 Example of an AWW MKC AWW 011734 WW 75 TORNADO TX OK AR 011800Z 020000Z AXIS80 STATUTE MILES EAST AND WEST OF A LINE60ESE DALDALLAS TX 30 NW ARG WALNUT RIDGE AR AVIATION COORDS 70NM EW 58W GGG 25NW ARG HAIL SURFACE AND ALOFT1 3 INCHES WIND GUSTS70 KNOTS MAX TOPS TO 450 MEAN WIND VECTOR 24045 Soon after the AWW goes out the actual watch bulletin itself is issued A WW is in the following format 1 Type of severe weather watch watch area valid time period type of severe weather possible watch axis meaning of a watch and a statement that persons should be on the lookout for severe weather 2 Other watch information ie references to previous watches 3 Phenomena intensities hail size wind speed knots maximum CB tops and estimated cell movement mean wind vector 4 Cause of severe weather 5 Information on updating ACs Example of a WW BULLETIN IMMEDIATE BROADCAST REQUESTED TORNADO WATCH NUMBER 381 STORM PREDICTION CENTER NORMAN OK 556 PM CDT MON JUN 2 1997 THE STORM PREDICTON CENTER HAS ISSUED A TORNADO WATCH FOR PORTIONS OF NORTHEAST NEW MEXICO TEXAS PANHANDLE EFFECTIVE TPHS MONDAY NIGHT AND TUESDAY MORNING FROM 630 PM UNTIL MIDNIGHT CDT TORNADOES HAIL TO 2 3 INCHES IN DIAMETER THUNDERSTORM WIND GUSTS TO 80 MPH AND DANGEROUS LIGHTNING ARE POSSIBLE IN THESE AREAS THE TORNADO WATCH AREA IS ALONG AND 60 STATUTE MILES NORTH AND SOUTH OF A LINE FROM 50 MILES SOUTHWEST OF RATON NEW MEXICO TO 50 MILES EAST OF AMARILLO TEXAS REMEMBER A TORNADO WATCH MEANS CONDITIONS ARE FAVORABLE FOR TORNADOES AND SEVERE THUNDERSTORMS IN AND CLOSE TO THE WATCH AREA PERSONS IN THESE AREAS SHOULD BE ON THE LOOKOUT FOR THREATENING WEATHER CONDITIONS AND LISTEN FOR LATER STATEMENTS AND POSSIBLE WARNINGS OTHER WATCH INFORMATION CONTINUE WW 378 WW 379 WW 380 DISCUSSION THUNDERSTORMS ARE INCREASING OVER NE NM IN MOIST SOUTHEASTERLY UPSLOPE FLOW OUTFLOW BOUNDARY EXTENDS EASTWARD INTO THE TEXAS PANHANDLE AND EXPECT STORMS TO MOVE ESE ALONG AND NORTH OF THE BOUNDARY ON THE N EDGE OF THE CAP VEERING WINDS WITH HEIGHT ALONG WITH INCREASGING MID LVL FLOW INDICATE A THREAT FOR SUPERCELLS 443 December 1999 AVIATION TORNADOES AND AFEW SEVERE THUNDERSTORMS WITH HAIL SURFACE AND ALOFT TO 2 3 INCHES EXTREME TURBULENCE AND SURFACE WIND GUSTS TO 70 KNOTS A FEW CUMULONIIVIBI WITH MAXIMUM TOPS TO 550 MEANS STORM MOTION VECTOR 28025 Status reports are issued as needed to show progress of storms and to delineate areas no longer under the threat of severe storm activity Cancellation bulletins are issued when it becomes evident that no severe weather will develop or that storms have subsided and are no longer severe When tornadoes or severe thunderstorms have developed the local WFO of ce will issue the warnings covering those areas 4F 4 u I W GEOGRAPHICAL AREA DESIGNATOR MAP Inn 1 COMMON TERMS USED IN AVIATION WEATHER FORECASTS tr 0 K 539 7 I 395 39 I s 5 ga n 00 39IIx s 5 734 Pm mum y quot139quot 1 2 S C wuquot quot usrm x 39 quotm c mu um amigo hm x ml 3 f 5 lquot u 05quotquot I I 4quot ml um g i 7 0 b 57 5quot r a I IT39S 4quot 3 k igm iwcw w u rr 6 5 c 39 39 79 rmmm s f a I E c T I m MIL 39 miI quot quotF Comm 39 us mm Is I 1 I I mm quotW WWW I s I I Vic I 1 mmquot 39 39 quot1 ms 3 I 5 I 39 quot 5 I quotI fquot 15 I m Sr 5 E 5 quotmm IIRITquot W no law f P x 5 I mquot I m5 I 3 3 equot 1 call SM I l i l 26 u I Vbe u 111 g k m Jam J I a IvI mm 4 a 5 z 139 l mm mm I 4 quotMum It wh 39Iaf 9 g isom 5 ml 4 WENquot it If g quotf R 6 WEI quotmquot Iit nlnuE lu xfllu n39 E99915 ms mm rll I Q Q 839 II quotIt EA JM m 9 nu tummy f ri I 1 I ssquot II 5 3 Elmum 5quotquot x 3 139 39 m w m SKA 1 II Inquot 5 m i SI m rquot n m M 39 t t w T W 3939 I 0 6 mu I g t iffy If 35 9 uquot quotUn quotl 07 quotquotquotE39mquot 3 rm mm quot Rbsx Q 1 m K s c I Sam I h 39 x 39 L n 12 mm GREAT ur39 39quot quot quot 1 ml ILL UL 49931351 1 a i p i I 4 Tlfymunuml gu 1 Hm 1m mums I Immumhl I l ln um I quotI g nll rl lv m l Eigulig I my 4 5 L l 2 531 39 Q m muw may 5 m 39 5 p 13 49 I g n Hwy ms mu39 quot a a nu quot 139 r I I quot 51 min I u I 1 4 1 m SE 19 E Inquot it u I Lll vs 3 quot3155 III quotInna la ll39l quotivlls39m MU I u quot SE I 5 2 22 a m S an lt e 39zrsn I ILL E39 2quot 5quot Wm 6 I 39nquot quot quotquot man Pums 3 39k Iiiiig ru I quot quotquot III 393quot r I I 9 1 E 13940 394 x f InI39I quotmLIus I inrnmnms tum r lfff 39 mquotmuggy m mus um 39 79 g a my mum V lmirunl mm v n J 1 um I nu 1m i kquot u a t 311 8 M 39 5 5 3 1 mssounl OIIRKS 4 6 jumpy in n u sung E 3 mm b a nuquot quot5quot 39 quot n 39 In I m mm H I uumls nu SAIHIIIIII o 395 v H o y 5 Mm noI39m w n a f nonmn IOITREISI Hillr Slimquot l 1iquot 1 J 0 sum IOIICI quot 39 mm o x h 9 m A 3 6 i S L mu m mm I a aw a r a cs I s is ms nu 7quot 3 quot39l I u Hm 056 a C soumm 1 um um um ulc39uuuu E m I h IWrnr x C NORTHWEST soumus mt or sun c tllrrmi H quot 9 um g 5 5 n cmuu nuns g ER M1 quot 5 C23 TEX 3 s x r 39 E 1 mm cmnu swarm 39 E 3 mis t um i m SOUTHEIST 30qu u SOUTH C E RTRAL S TOO MILES OUTWARD FROM COAST COISTAL WATER AM s m l m msm am w s 1 I a 51 391 I 4 UP h39u KEYS 0 3 T I 0 ea quot11 mm IIng V v I 0 m FLORIOA mumgt1 i V Figure 411 Geographical Areas and Terrain Features 6661 leqweoecr December 1999 December 1999 Section 5 SURFACE ANALYSIS CHART The surface analysis chart is a computergenerated chart with frontal analysis by HPC forecasters transmitted every 3 hours covering the contiguous 48 states and adjacent areas Figure 51 is a surface analysis chart and Figure 52 illustrates the symbols depicting fronts and pressure centers VALID TIME Valid time of the chart corresponds to the time of the plotted observations A datetime group in Universal Coordinated Time UTC tells the user when conditions portrayed on the chart occurred ISOBARS Isobars are solid lines depicting the sealevel pressure pattern and are usually spaced at intervals of 4 millibar mb or hectoPascals hPa in metric units 1 millibar l hectoPascal Each isobar is labeled For example 1032 signi es 10320 mb hPa 1000 signi es l0000 mb hPa and 992 signi es 9920 mb hPa PRESSURE SYSTEMS The letter L denotes a low pressure center and the letter H denotes a high pressure center The pressure of each center is indicated by a three or fourdigit number that is the central pressure in mb hPa FRON TS The analysis shows positions and types of fronts by the symbols in Figure 52 The symbols on the front indicate the type of front and point in the direction toward which the front is moving If the front has arrowheadshaped symbols it is a cold front Ifthe front has halfmoon symbols it is a warm front A threedigit number near a front classifies it as to type see Table 51 intensity see Table 52 and character see Table 53 A bracket or before or after the number points to the front to which the number refers For example in Figure 51 the front extends from eastern Montana into central North Dakota south through South Dakota and Nebraska into northwestem Kansas The front is labeled 027 which means a quasistationary front 0 from Table 51 weak little or no change 2 from Table 5 2 and with waves 7 from Table 53 Two short lines across a front indicate a change in classification In figure 51 note that two lines cross the front in central Montana adjacent to the Low To the left of the Low the front is numbered 450 which is a cold front moderate little or no change and no specification The front to the right of the Low is numbered 027 which is a quasistationary front weak little or no change and with waves TROUGHS AND RIDGES A trough of low pressure with signi cant weather will be depicted as a thick dashed line running through the center of the trough and identi ed with the word TROF The symbol for a ridge of high pressure is very rarely if at all depicted Figure 52 December 1999 OTHER INFORMATION The observations from a number of stations are plotted on the chart to aid in analyzing and interpreting the surface weather features These plotted observations are referred to as station models There are two primary types of station models plotted on the chart Those with a round station symbol are observations taken by observers The locations with a square station symbol indicate the sky cover was determined by an automated system Other plotting models that appear over water on the chart are data from ships buoys and offshore oil platforms Figure 53 is an example of a station model that shows where the weather information is plotted Figures 54 through Figure 57 help explain the decoding of the station model An outflow boundary will be depicted as a thick dashed line with the word OUTBNDY A dry line will be depicted as a line with unshaded pips or a through symbol It will also be identified with the words DRY LINE A legend is printed on each chart stating its name valid date and valid time USING THE CHART The surface analysis chart provides a ready means of locating pressure systems and fronts It also gives an overview of winds temperatures and dew point temperatures at chart time When using the chart keep in mind that weather moves and conditions change Using the surface analysis chart in conjunction with other information gives a more complete weather picture r238 6 9 9 wz w 1 R 3899 b 395 rw x6 1 w 6 22 3 56 I 10 0 03 th366 IA 13 gure 5 1 Surface Analysi Chart 011N188 T on 6661 leqweosa December 1999 Color Blue Red Blue Red RedBlue Purple Blue Red RedBlue Blue Red RedBlue Purple Purple Brown Brown Yellow Description High Pressure Center Low Pressure Center Cold Front Warm Front Stationary Front Occluded Front Cold Frontogenesis Warm Frontogenesis Stationary Frontogenesis Cold Frontolysis Warm Frontolysis Stationary Frontolysis Occluded Frontolysis Squall Line Dryline Trough Ridge Figure 52 Symbols on Surface Analysis Chart December 1999 HIGH CLOUD TYPE TOTAL SKY COVER MIDDLE CLOUD TYPE WIND SPEED I SEALEVEL PRESSURE WIND DIRECTION PRESSURE CHANGE IN 147 PAST 3 HOURS TEMPERATURE 34 PRESENT WEATHER x 28 lt PRESSURE TENDENCY DEW POINT 32 LOW CLOUD TYPE 45 lt 6 HOUR PRECIPITATION 1 Total sky cover Overcast 2 Temperature 34 degrees F Dew Point 32 degrees F 3 Wind From the northwest at 20 knots relative to true north Examples of wind direction and speed fjfuj CALM NORTHEAST SOUTHWEST NORTH AT WEST AT SOUTH AT AT 5 KNOTS AT 10 KNOTS 15 KNOTS 50 KNOTS 60 KNOTS uh Present Weather Continuous light snow 5 Predominate low middle high cloud reported Strato fractus or cumulus fractus of bad weather altocumulus in patches and dense cirrus 6 Sealevel pressure 10147 millibars mbs NOTE Pressure is always shown in three digits to nearest tenth of an mb For 1000 mbs or greater pre x a quot10quot to the three digits For less than 1000 mbs pre x a quot9quot to the three digits 7 Pressure change in the past 3 hours Increased steadily or unsteadily by 28 mbs The actual change is in tenths of a mb 8 6 hour precipitation in hundredths of an inch 45 hundredths of an inch Figure 53 Station Model and Explanation 55 December 1999 Table 5 1 Type of Front Table 5 2 Intensity of Front Table 5 3 Character of Front GGGQ Clear FEW BKN 08 lt18 28 38 48 58 78 Figure 54 Sky Cover Symbols 690 0 December 1999 Breaks in overcast OVC 88 Total sky obscuration 88 Missing cloud or sky cover observation or partial obscuration December 1999 Description of Characteristic Primary Additional COde Requirements Requirements Graphic Figure Increasing then decreasing 0 Increasing then steady or Increasing then increasing H39gher more slowly I Atmospheric Wefmlng pressure now steadily or unsteadily 2 hlgher than 3 lieu cabling 01 steady hours ag0 then increasing or Increasing then increasing more rapidly 3 Same Increasing then decreasing 0 Atmospheric Steady 4 pressure now same as 3 hours beu easing then 1ncreas1ng 5 ago Decreasing then increasing 5 Dec easing thequot steady u Lower Decreasrng then decreas1ng Atmospheric more slowly 6 pressure now lower than 3 Decreasmg hours ago steadily or unsteadily 7 Steady or increasing then decreasing or DELI caning tilell JUL caning 8 more rapidly Figure 55 Pressure Tendencies 639S 10 30 40 50 60 70 80 90 Cloud development NOT observed or NOT observable during past hour Light iog ireezing and at time of observation S39ll storm or sandstorm has W 00 S 839 Dust storm or sandstorm within sight oi or at station during past hour Funnel clouds within Clouds generally dissolving State oi the sky on Chm Ee jmlly 0quot E Visibility reduced by smoke Visibility reduced by haze J J NOT J J 39 J J 39 J 39 i r r n d g past 1mm during past 11mm hour raised by the wind at time oi observation O v 39 39 hm 39 39 39 39 39 39 Thunder heard but no Squalls within sight at station NOT deeper shallow iog at station NOT mum hemp NOT39 39 i e 39 5 k 0 1 1 139 391 6 k quot1quot distant irom station to but NOT at station 39 39 N V V V Rain NOT ireezing and NOT ialling as showers during past hour but NOT at time oi observation storm or sandstorm no Snow NOT ialling as o observa 39on storm or sandstorm has 96 of ob servation sandstorm has decreased hour E Fog at distance at time oi observation but NOT at station during past hour 9 during past hour Fog in patches Continuous drizzle NOT freezing slight at time oi observation Fog sky discemible Fog sky NOT discemible rain NOT ialling as showers during pa t hour but NOT at ervation n r r past hour but NOT at J tim oi observation e oi obs Severe dust storm or sandstorm asin eased sandstorm no appreciable h dunng past h change during pas hour mm Fog sky discemible Fog sky NOT discemible or oi rain and snow during past hour but NOT at time oi observation Slight or moderate 39 ting snow generally low Fog sky discernible a neg during past hour freezing moderate at time oi observation during past hour 9 99 i mm freezing moderate at time oi observation 39 39 NOT freezing slight at time oi observation X 39 39 NOT freezing slight at time oi observation 96 Intermi ent fall of snow akes Continuous fall of snow akes tt slight at time oi observation 6 slight at time oi observation V 39 39 NOT freezing moderate at NO freezing moderate at r n during past hour 9 9 9 9 9 9 freezing thick at time freezing thi at time oi observation of observation mm freezing heavy at freezing heavy at 39 r L time oi observation Intermittent iall oi snow akes moderate at time of observation V 9 X39 Continuous iall oi snow akes moderate at time oi observation 0 G V 6 Moderate or heavy showers oi hail with t rain or raln an s w mixed NOT associated with thunder rain showers l i Slight rain at time of observation thunderstorm but NOT at time of observation hour but NOT at time of observation rain and snow mixed a hour but NOT at time of observation x x 9 96 Continuous all of snow akes heavy at time of observation Int 39ttent iall oi snow akes heavy at time oi observation 0 V V Moderate or heavy slight snow showers showers oi ram and snow mixed quot hail ox fnow Slight or moderate hour but NOT at time of ob 39 Slight ireezing drizzle J Showers oi hail or oi hail and rain durin past hour but NOT at oi observation lleavy driiting snow generally low Fog sky NOT discernible has begun or become N Moderate or thick ireezing drizzle Fog during past hour but NOT at time oi observation Slight or moderate driiting snow generally high i Fog depositing rime sky discemible Drizzle and rain slight 0 R Thunderstorm with or without precipitation during past hour but NOT at time oi observation lleavy driiting snow generally high E Fog depositing rime sky NOT discemible D e and rain moderate or heavy O Rain o 39 light Min 39 ireezing rain moderate or heavy H e N A Ice needles W39I39h Granular snow with Isolated starlike snow I pellets sleet US or Whom fog or without fog uystals with or without dermalom fog X V Moderate or heavy snow showers A K Slight or moderate Figurem gIO Present Weather Symbols 6 Slight showers oi soit or sm h 39 39 39tho t rain or rain and now lleavy thnnderstorm without hail but with rain observation A V Moderate or heavy showers oi soit or small hail 39 or without 39 snow Thunderstorm combined with dust i at time of observation Slight showers oi hail with or without rain or rain and snow mixed NOT associated with thunder A 17 Heavy thunderstorm with hail at time of observation 6661 leqweoeq OI39S CLOUD ABBREVIATION DESCRIPTION Abridged from WMO Code 0 DESCRIPTION Abridged from WMO Code DESCRIPTION Abridged from WMO Code St or F5 Stratus or Fractostratus Ci Cirrus Cs Cirrostratus Cc Cirrocumulus Ac Altocumulus As Altostratus IMDDDH Sc Stratocumulus Ns Nimbostratus Cu or Fc Cumulus or Fractocumulus D4 Cb Cumulonimbus DOOQG39NUIBUJNh t Cu fair weather little vertical development and attened Cu considerable development towering with or without other Cu or Sc bases at same level Cb with tops lacking clearcut outlines but distinctly not cirroform or anvil shaped with or without Cu Sc or St Sc formed by spreading out of Cu Cu often present also Sc not formed by spreading out of Cu St or Fs or both but no Fs of bad weather Fs andor Fc of bad weather scud Cu and Sc not formed by spreading out of Cu with bases at different levels Cb having a clearly fibrous cirroform top often anvil shaped with or without Cu Sc St or scud OOQGUIBUJNh t 9 M 4 W J 4 W 4 H J Thin As most of cloud layer is semitransparent Thick As greater part sufficiently dense to hide sun or moon or Ns Thin Ac mostly semitransparent cloud elements not changing much at a single level Thin Ac in patches cloud elements continually changing andor occurring at more than one level Thin Ac in bands or in a layer gradually spreading over sky and usually thickening as a whole Ac formed by the spreading out of Cu Doublelayered Ac or a thick layer of Ac not increasing or Ac with As andor N s Ac in the form of Cu shaped tufts or Ac with turrets Ac of chaotic sky usually at different levels patches of dense Ci are usually present DOOQG39NUIBUJNh t 8LENI JLL a Filaments of Ci or quotmares tailsquot scattered and not increasing Dense Ci in patches or twisted sheaves usually not increasing sometimes like remains of Cb or towers tufts Dense Ci often anvil shaped derived from or associated Cb Ci often hook shaped gradually spreading over the sky an usually thickening as a whole Ci and Cs often in converging bands or Cs alone generally overspreading and growing denser the continuous layer not reaching 45 altitude Ci and Cs often in converging bands or Cs alone generally overspreading and growing denser the continuous layer exceeding 45 altitude Veil of Cs covering the entire sky Cs not increasing and not covering the entire sky Cc alone or Cc with some Ci or Cs but the Cc being the main cirroform cloud Figure 57 Cloud Symbols 6661 lsqwsosa December 1999 Section 6 WEATHER DEPICTION CHART The weather depiction chart Figure 63 is computergenerated with human frontal analysis from METAR reports The weather depiction chart gives a broad overview of the observed ying category conditions at the valid time of the chart This chart begins at OlZ each day is transmitted at 3hours intervals and is valid at the time of the plotted data PLOTTED DATA Observations reported by both manual and automated observation locations provide the data for the chart The right bracket indicates the present weather information was obtained by an automated system only The plotted data for each station are total sky cover cloud height or ceiling weather and obstructions to vision and visibility Ifthe stations on the chart are crowded together the weather visibility and cloud height may be moved up to 90 degrees around the station for better legibility When reports are frequently updated as at some automatic stations every 20 minutes or when the weather changes signi cantly the observation used is the latest METAR received instead of using the one closest to the stated analysis time TOTAL SKY COVER The amount of sky cover is shown by the station circle shaded as in Figure 61 Clear 08 Breaks in overcast FEW lt18 28 ovc 88 SCT 38 48 Total sky obscuration 88 BKN 58 78 Missing cloud or sky cover observation or partial obscuration 09 0 690 v Figure 61 Total Sky Cover 61 December 1999 CLOUD HEIGHT Cloud height above ground level AGL is entered under the station circle in hundreds of feet the same as coded in a METAR report Iftotal sky cover at a station is scattered the cloud height entered is the base of the lowest scattered cloud layer If total sky cover is broken or greater at a station the cloud height entered is the lowest broken or overcast cloud layer A totally obscured sky is shown by the sky cover symbol X and is accompanied by the height entry of the obscuration vertical visibility into the obscuration A partially obscured sky without a cloud layer above however is not recognized by the computer program reading the METAR report It cannot differentiate between a partial obscuration and a missing observation Therefore the computer program will enter an M in the sky cover circle for either occurrence Consequently the user will not know if the observation is missing or a partial obscuration is present To obtain the most accurate information the user must consult the METAR report for that speci c station A partially obscured sky with clouds above will have a cloud height entry for the cloud layer but there will be no entry to indicate that there is a partial obscuration at the surface So once again the user must consult the METAR report to obtain the most accurate information WEATHER AND OBSTRUCTION S TO VISIBILITY Weather and obstructions to visibility symbols are entered to the left of the station circle Figure 56 explains most of the symbols used When several types of weather and or obstructions to visibility are reported at a station the first one reported in the METAR would usually be the highest coded number in Figure 56 Also for some stations that are not ordinarily plotted the weather symbol is plotted only if the weather is signi cant such as a thunderstorm VISIBILITY When visibility is 5 miles or less it is entered to the left of the weather or obstructions to vision symbol Visibility is entered in statute miles and fractions of a mile December 1999 Total sky obscuration and the vertical visibility into the obscuration is 300 feet 1 4 visibility fog bracket indicates fog was determined by an automated system 3 FEW sky coverage no cloud height is indicated with FEW 5 CO CD SCT sky coverage cloud height 3000 AGL visibility 5 miles haze 30 3 BKN sky coverage ceiling height 2000 AGL visibility 3 miles continuous rain 20 l X OVC sky coverage ceiling height 500 AGL visibility 1 mile intermittent snow 5 SCT sky coverage cloud height 25000 AGL 250 O l 12 BKN sky coverage ceiling height 1000 AGL visibility 112 mile thunderstorm with rain shower 1 0 Missing cloud or sky cover observation or partial obscuration Figure 62 Examples of Plotting on the Weather Depiction Chart 63 December 1999 ANALYSIS The chart shows observed ceiling and visibility by categories as follows IFR Ceiling less than 1000 feet andor visibility less than 3 miles hatched area outlined by a smooth line MVFR Marginal VFR Ceiling 1000 to 3000 feet inclusive andor visibility 3 to 5 miles inclusive nonhatched area outlined by a smooth line VFR No ceiling or ceiling greater than 3000 feet and visibility greater than 5 miles not outlined The three categories are also explained in the lower right portion of the chart for quick reference In addition the chart shows fronts and troughs from the surface analysis for the preceding hour with one exception being that fronts and troughs are omitted on the 10Z and 23Z charts These features are depicted the same as the surface chart Because space on the chart is limited only about half the METAR reports are plotted on the chart The areas for each ight category are determined using all available reports whether or not they are plotted USING THE CHART The weather depiction chart is an ideal place to begin preparing for a weather brie ng and ight planning From this chart one can get a bird s eye view of areas of favorable and adverse weather conditions for chart time This chart may not completely represent the en route conditions because of variations in terrain and possible weather occurring between reporting stations Due to the delay between data and transmission time changes in the weather could occur One should update the chart with current METAR reports After initially sizing up the general weather picture final ight planning must consider forecasts progs and the latest pilot radar and surface weather reports 5 quot 4039 WinW 39 4wi A I 1 i 8 2 gym 21 I v 6bf10 866I NVP 80 nHl ZTO39 COLD IT2 a o 100 a I an NXMSUM AKJNISMNSUDN nugwn in ma sn Q 6 TofnL srn IONS r I am 5 E Finn amquot 51 1133i EllIi 0F 1 I 0130 39 iv Mm IFRHTHEszESIHRN o 39 I 39 39 1000 FT Fl IOR VSBV L SSTHR 3 MI EONTOLIRED H39ITHO I SHRDING MVF WW I RAS PL innsm gs THRN nmunls39Tnap s n o ER HaN R E0LIRL In 40 04 Ew LIIB 5 m 0 IS LITUmITIE Mr 393 3 zz253zsgasas m k a HEATHER DEE ICTIQNo 12 TjHU as JAN 1998 O G vm39 rmsns HIIH SIULSaIN e WW a i ma THRN Imam 3000 FT N VSBV GRERTER 39THRN 5 N Figure 63 Weather Depiction Chart December 1999 December 1999 Section 7 RADAR SUMMARY CHART A radar summary chart Figure 71 is a computergenerated graphical display of a collection of automated radar weather reports SDs This chart displays areas of precipitation as well as information about type intensity con guration coverage echo top and cell movement of precipitation Severe weather watches are plotted if they are in effect when the chart is valid The chart is available hourly with a valid time of H35 ie 35 minutes past each hour Figure 72 depicts the WSR SSD radar network from which the radar summary chart is developed ECHO gERECIPITATIO j TYPE The types of precipitation are indicated on the chart by symbols located adjacent to precipitation areas on the chart Table 71 lists the symbols used to denote types of precipitation Note that these symbols do not re ect the change to METAR Since the input data for the radar summary chart are the automated SDs the type of precipitation is determined by computer models and is limited to the ones listed in Table Table 7 1 Key to Radar Chart Symbols Used on Chart Sym bol Meaning Sym bol Meaning R Rain 35 Cell movement to the 1 northeastat 35 knots RW Rain shower LM Little movement S Snow Severe thunderstorm watch SW Snow shower number 999 T Thunderstorm Tornado watch number 210 NA Not available 810 or greater coverage NE N0 echoes in a line OM Out for maintenance Line of echoes December 1999 INTENSITY The intensity is obtained from the amount of energy returned to the radar from the target and is indicated on the chart by contours Six precipitation intensity levels are reduced into three contour intervals as indicated in Table 72 In Figure 71 over central Montana is an area of precipitation depicted by one contour The intensity of the precipitation area would be light to possibly moderate Whether there is moderate precipitation in the area cannot be determined However what can be said is that the maximum intensity is de nitely below heavy When determining intensity levels from this chart it is recommended that the maximum possible intensity be used To determine the actual maximum intensity level the SD for that time period should be examined It should also be noted that intensity is coded for frozen precipitation ie snow or snow showers This is due to the fact that the WSR88D is much more powerful and sensitive than previous radars Finally it is very important to remember that the intensity trend is no longer coded on the radar summary chart Table 7 2 Precipitation Intensities Digit Precipitation Rainfall Rate Rainfall Rate Highest precipitation top in area in hundreds of feet MSL 45000 feet MSL ECHO CONFIGURATION AND COVERAGE The con guration is the arrangement of echoes There are three designated arrangements a LINE of echoes an AREA of echoes and an isolated CELL See Radar Weather Reports in Section 3 for de nitions of the three con gurations Coverage is simply the area covered by echoes All the hatched area inside the contours on the chart is considered to be covered by echoes When the echoes are reported as a LINE a line will be drawn through them on the chart Where there is 810 coverage or more the line is labeled as solid SLD at both ends In the absence of this label it can be assumed that there is less than 8 10 coverage For example in Figure 71 there is a solid line of thunderstorms with intense to extreme rain showers over central Georgia December 1999 ECHO TOPS Echo tops are obtained from both radar and on occasion satellite data and displayed for precipitation tops Echo tops are the maximum heights of the precipitation in hundreds of feet MSL They should be considered only as approximations because of radar wave propagation limitations Tops are entered above a short line with the top height displayed being the highest in the indicated area Examples maximum top 22000 feet Maximum top 50000 feet It is assumed that all precipitation displayed on the chart is reaching the surface Some examples of top measurements in Figure 71 include a top of 15000 feet MSL over northeast Washington 23000 feet over northcentral Texas and 32000 feet MSL in central Georgia ECHO MOVEMENT Individual cell movement is indicated by an arrow with the speed in knots entered as a number at the top of the arrow head Little movement is identified by LM For example in Figure 71 the precipitation over northcentral Texas is moving southwest at 8 knots The precipitation in New England area is moving eastnortheast at 25 knots Line or area movement is no longer indicated on the chart SEVERE WEATHER WATCH AREAS Severe weather watch areas are outlined by heavy dashed lines usually in the form of a large rectangular box There are two types tornado watches and severe thunderstorm watches Referring to Figure 71 and Table 71 the type of watch and the watch number are enclosed in a small rectangle and positioned as closely as possible to the northeast comer of the watch box For example in Figure 71 the boxed WS0005 in northeast Georgia and western South Carolina is a severe thunderstorm watch and is the 539h severe thunderstorm watch issued so far in the year The watch number is also printed at the bottom of the chart in Mexico together with the issuance time and expiration time USING THE CHART The radar summary chart aids in pre ight planning by identifying general areas and movement of precipitation and or thunderstorms This chart displays drops or ice particles of precipitation size only it does not display clouds and fog Therefore the absence of echoes does not guarantee clear weather and cloud tops will most likely be higher than the tops of the precipitation echoes detected by radar The chart must be used in conjunction with other charts reports and forecasts Examine chart notations carefully Always determine location and movement of echoes If echoes are anticipated near the planned route take special note of echo intensity Be sure to examine the chart for missing radar reports before assuming no echoes present For example the Rapid City RAP radar report in western South Dakota is shown as not available NA Suppose the planned ight route goes through an area of widely scattered thunderstorms in which no increase in area is anticipated If these storms are separated by good VFR weather they can be visually sighted and circumnavigated However widespread cloudiness may conceal the thunderstorms To avoid these embedded thunderstorms either use airborne radar or detour the area Remember that the radar summary chart is for pre ight planning only and should be updated by current WSR 88D images and hourly reports Once airborne the pilot must evade individual storms by inflight 73 December 1999 observations This can be done by using visual sighting or airborne radar as well as by requesting radar echo information from Automated Flight Service Station AF SS Flight Watch The AF SS Flight Watch has access to current WSR SSD imagery There can be an interpretation problem concerning an area of precipitation that is reported by more than one radar site For example station A may report RW with cell movement toward the northeast at 10 knots For the same area station B may be reporting TRW with cell movement toward the northeast at 30 knots This difference in reports may be due to a different perspective and distance of the radar site from the area of echoes The area may be moving away from station A and approaching station B The rule of thumb is to use that plotted data associated with the area that presents the greatest hazard to aviation In this case the station B report would be used ucoaL mu uq gym 177 num In uzuEz yam 0252 50 L0 nL HgRNINGRRDRRSquot P 5L9 JK nvx H wjr R NX 39ug39uz39imzlgui ETQ LNNING hahkur 3n HINUIES sum E IN TIME moss my NFLy nLHnn ESU39IP PBLMS MEGMIS I REPDRT E s a m 7382 am VER 652 5458 UHE R QND LETED HIN DELETED 6 TS 1uu BURN REV RT 39 ngnsgsn N o WAX 0x quot 3 wan HER umcu nREns mmnREnsLINEsPENIENTS RR 1 5mm END NAV HVMZEELLSRRRDHS HI H SEEED H5 DIN 20332 03002 J 39 39 R IF TVPE nND EHRNG or INTENsu g W s N H DR INERG s DLRG 39 v 65E7J7C5392 39 39 39 39 439 NE 0sz THUQBOS JAN 1998 ADAR 1 K110 K 90 i 39 A v 07 Figure 71 Radar Summary Chart 869 December 1999 COMPLETED WSR88D INSTALLATIONS I Marh17199 1 F I 94 f 45quot 9 1 14 54 39v 3 r X 5 61 if 150 v A AL My 6 egg ALASKA AZORES 39 SOUTH KOREA OKINAWA 4 1 I K 6 332ch w y HAWAII W k V GUAMr pUERTO RICO KAUAI r 6493 LOKAI Lia 534534 W15 All o ENSET My v 9 OPERATIONAL SUPPORT FACILITY 5 NORMAN OKLAHOMA Figure 72 WSR88D Radar Network 76 December 1999 Section 8 CONSTANT PRESSURE ANALYSIS CHARTS Weather information for computer generated constant pressure charts is observed primarily by balloon ascending radiosonde packages Each package consists of weather instruments and a radio transmitter During ascent instrument data are continuously transmitted to the observation station Radiosondes are released at selected observational sites across the USA at OOZ and 12Z The data collected from the radiosondes are used to prepare constant pressure charts twice a day Constant pressure charts are prepared for selected values of pressure and present weather information at various altitudes The standard charts prepared are the 850 mb hPa 700 mb hPa 500 mb hPa 300 mb hPa 250 mb hPa and 200 mb hPa charts Charts with higher pressures present information at lower altitudes and charts with lower pressures present information at higher altitudes Table 81 lists the general altitude pressure altitude of each constant pressure chart PLOTTED DATA Data from each observation station are plotted around a station circle on each constant pressure chart The circle identifies the station position The data plotted on each chart are temperature temperature dew point spread wind height of the surface above sea level and height change of the surface over the previous 12hour period The temperature and spread are in degrees Celsius wind direction is relative to true north wind speed is in knots and height and height change are in meters The station circle is shaded black when the spread is 5 degrees or less moist atmosphere and open when spread is more than 5 degrees dry atmosphere Figure 81 illustrates a station model of the radiosonde data plot Table 82 gives station data plot examples for each constant pressure chart Aircraft and satellite observations are also used as information sources for constant pressure charts A square is used to identify an aircraft reporting position Data plotted are the ight level of the aircraft in hundreds of feet temperature wind and time to the nearest hour UTC A star is used to identify a satellite reporting position Satellite information is determined by identifying cloud drift and height of cloud tops Data plotted are the ight level in hundreds of feet time to the nearest hour UTC and wind Aircraft and satellite data are plotted on the constant pressure chart closest to their reporting altitudes Aircraft and satellite information are particularly useful over sparse radiosonde data areas ANALYSIS All constant pressure charts contain analyses of height and temperature variations Also selected charts have analyses of wind speed variations Variations of height are analyzed by contours variations of temperature by isotherms and variations of wind speed by isotachs CON TOURS Contours are lines of constant height in meters which are referenced to mean sea level Contours are used to map the height variations of surfaces that uctuate in altitude They identify and characterize pressure systems on constant pressure charts December 1999 Contours are drawn as solid lines on constant pressure charts and are identi ed by a threedigit code located on each contour To determine the contour height value affix quotzeroquot to the end of the code For example a contour with a quot315quot code on the 700 mbhPa chart identifies the contour value as 3150 meters Also af x a quotonequot in front of the code on all 200 mbhPa contours and on 250 mbhPa contours when the code begins with zero For example a contour with a quot044quot code on a 250 mbhPa chart identifies the contour value as 10440 meters The contour interval is the height difference between analyzed contours A standard contour interval is used for each chart The contour intervals are 30 meters for the 850 and 700 mb hPa charts 60 meters for the 500 mb hPa chart and 120 meters for the 300 250 and 200 mb hPa charts The contour gradient is the distance between analyzed contours Contour gradients identify slopes of surfaces that uctuate in altitude Strong gradients are closely spaced contours and identify steep slopes Weak gradients are widely spaced contours and identify shallow slopes The contour analysis displays height patterns Common types of patterns are lows highs troughs and ridges Contours have curvature for each of these patterns Contour patterns can be further characterized by size and intensity Size represents the breadth of a system Sizes can range from large to small A large pattern is generally more than 1000 miles across and a small pattern is less than 1000 miles across Intensities can range from strong to weak Stronger systems are depicted by contours with stronger gradients and sharper curvatures Weaker systems are depicted by contours with weaker gradients and weaker curvatures For example a chart may have a large weak high or a small strong ow Contour patterns on constant pressure charts can be interpreted the same as isobar patterns on the surface chart For example an area of low height is the same as an area of low pressure Winds respond to contour patterns and gradients Wind directions parallel contours In the Northern Hemisphere when looking downwind contours with relatively lower heights are to the left and contours with relatively higher heights are to the right Thus winds ow counterclockwise cyclonically around lows and clockwise anticyclonically around highs In the Southern Hemisphere these directions are reversed Winds that rotate are termed circulations Wind speeds are faster with stronger gradients and slower with weaker gradients In mountainous areas winds are variable on pressure charts with altitudes at or below mountain crests Contours have the effect of quotchannelingquot the wind ISOTHERMS Isotherrns are lines of constant temperature An isotherm separates colder air from warmer air Isotherrns are used to map temperature variations over a surface Isotherrns are drawn as bold dashed lines on constant pressure charts Isotherm values are identified by a twodigit block on each line The two digits are prefaced by quotquot for abovefreezing values as well as the zero isotherm and quotquot for belowfreezing values Isotherrns are drawn at 5degree intervals on each chart The zero isotherm separates abovefreezing and belowfreezing temperatures Isotherm gradients identify the magnitude of temperature variations Strong gradients are closely spaced isotherms and identify large temperature variations Weak gradients are loosely spaced isotherms and identify small temperature variations December 1999 ISOTACHS Isotachs are lines of constant wind speed Isotachs separate higher wind speeds from lower wind speeds Isotachs are used to map wind speed variations over a surface Isotachs are analyzed on the 300 250 and 200 mb hPa charts Isotachs are drawn as short ne dashed lines Isotach values are identi ed by a two or threedigit number followed by a quotKquot located on each line Isotachs are drawn at 20knot intervals and begin at 10 knots Isotach gradients identify the magnitude of wind speed variations Strong gradients are closely spaced isotachs and identify large wind speed variations Weak gradients are loosely spaced isotachs and identify small wind speed variations Zones of very strong winds are highlighted by hatches Hatched and unhatched areas are alternated at 40knot intervals beginning with 70 knots Areas between the 70 and llOknot isotachs are hatched Areas between the 110 and lSOknot isotachs are unhatched This alternating pattern is continued until the strongest winds on the chart are highlighted Highlighted isotachs assist in the identi cation of et streams THREE DIMENSIONAL ASPECTS It is important to assess weather in both the horizontal and vertical dimensions This not only applies to clouds l 391 quot quot and other 39 T conditions but also pressure systems and winds The characteristics of pressure systems vary horizontally and vertically in the atmosphere The horizontal distribution of pressure systems is depicted by the constant pressure charts and the surface chart Section 5 Pressure systems appear on each pressure chart as pressure patterns Pressure charts identify and characterize pressure systems by their location type size and intensity The vertical distribution of pressure systems must be determined by comparing pressure patterns on vertically adjacent pressure charts For example compare the surface chart with the 850 mbhPa chart 850 mbhPa with 700 mbhPa and so forth Changes of pressure patterns with height can be in the form of position type size or intensity The threedimensional assessment of pressure systems infers the assessment of the threedimensional variations of wind USING THE CHARTS Constant pressure charts are used to provide an overview of selected observed en route ying conditions Use all pressure charts for a general overview of conditions Select the chart closest to the desired ight altitude for assessment of en route conditions Review the winds along the route Consider their direction and speed For high altitude ights identify jet stream positions Note whether pressure patterns cause signi cant wind shifts or speed changes Determine if these winds will be favorable or unfavorable tailwind headwind crosswind Consider vertically adjacent charts and determine if a higher or lower altitude would have a more desirable en route wind Interpolate winds between charts for ights between chart levels Review other conditions along the 83 December 1999 route Evaluate temperatures by identifying isotherm values and patterns Evaluate areas with moist air and cloud potential by identifying station circles shaded black Consider the potential for hazardous ight conditions Evaluate the potential for icing Freezing temperatures and visible liquid forms of moisture produce icing Evaluate the potential for turbulence In addition to convective conditions and strong surface winds turbulence is also associated with wind shear and mountain waves Wind shear occurs with strong curved ow and speed shear Strong lows and troughs and strong isotach gradients are indicators of strong shear Vertical wind shear can be identified by comparing winds on vertically adjacent charts Mountain waves are caused by strong perpendicular ow across mountain crests Use winds on the pressure charts near mountain crest level to evaluate mountain wave potential Pressure patterns cause and characterize much of the weather As a general rule lows and troughs are associated with clouds and precipitation while highs and ridges are associated with good weather However this rule is more complicated when pressure patterns change with height Compare pressure pattern features on the various pressure charts with other weather charts such as the weather depiction and radar summary charts Note the association of pressure patterns on each chart with the weather Pressure systems winds temperature and moisture change with time For example pressure systems move change size and change intensity Forecast products predict these changes Compare observed conditions with forecast conditions and be aware of these changes December 1999 HGT HCLVM TT TD Code I Explanation WIND HGT TT CIRCLE Plotted wind direction and speed by symbol Direction is to the nearest 10 degrees and speed is to the nearest 5 knots See Figure 53 for the explanation of the symbols If the direction or speed is missing the wind symbol is omitted and an quotMquot is plotted in the HC space If speed is less than 3 knots the wind is light and variable the wind symbol is omitted and an quotLVquot is plotted in the HC space Plotted height of the constant pressure surface in meters above mean sea level See Table 81 for decoding If data is missing nothing is plotted in this position Plotted temperature to the nearest whole degree Celsius A belowzero temperature is prefaced with a minus sign Position is left blank if data is missing A bracketed computer generated temperature is plotted on the 850 mbhPa chart in mountainous regions when stations have elevations above the 850 mbhPa pressure level If two temperatures are plotted one above the other the top temperature is used in the analysis Plotted temperaturedew point spread to the nearest whole degree Celsius An quotXquot is plotted when the air is extremely dry The position is left blank when the information is missing Plot of constant pressure surface height change which occurred during the previous 12 hours in tens of meters For example a 04 means the height of the surface rose 40 meters and a 12 means the height fell by 120 meters HC data is superseded by quotLVquot or quotMquot when pertinent Identifies station position Shaded black when TD spread is 5 degrees or less moist Unshaded when spread is more than 5 degrees Figure 81 Radiosonde Data Station Plot 85 December 1999 Table 81 Features of the Constant Pressure Charts US Decode Examples of Station Station Height 2 Height Plot Plotting 63 g g T 3 1 1 3 8 5 a 5 E E a 3 a 3 3 i lt1 3 g T g a g 5 E s E E 2 E 2 3 3 2 a E m a w 3 s gt s gt a e a 5 E a a a 5 E S 5 a 8 we 8 8 E a E a E a g m g g a g E g g a 5 a v a H a o a a 3 a a m 850 5 000 1 500 yes no 30 1 530 1530 700 10000 3000 yes no 30 2 0r 3 180 3180 500 18000 5500 yes no 60 0 582 5820 300 30000 9000 yesquot yes 120 0 948 9480 250 34000 10500 yesquot yes 120 1 0 063 10630 200 39000 12000 yesquot yes 120 1 0 164 11640 NOTE 1 The pressure altitudes are rounded to the nearest 1000 for feet and to the nearest 500 for meters All heights are above mean sea level MSL Pre x a 2 or 3 whichever brings the height closer to 3000 meters Omitted when the air is too cold temperature less than 41 degrees P N December 1999 Table 82 Examples of Radiosonde Plotted Data 22 479 09 129 19 558 46 919 55 037 60 191 03 O y 17 03 10 01 O 4 LV M 850 mb 700 mb 500 mb 300 mb 250 mb 200 mb light and 01020 KT 21060 KTS 27025 KTS 24030 KTS missing WIND variable TT 22 C 9 C 19 C 46 C 55 C 60 C T D 4 C 17 C gt29 C not plotted not plotted not plotted DEW POINT 18 C 8 C drV drV drV HGT 1479 m 3129 m 5580 m 9190 m 10370 m 11910 m 30 m 30 m 100 m 10 m not plotted Hc not plotted 0083an 500 V 5 9 hf ms 1 0 5 so 2 gt P ANALYSIS HEIGHTSITEMPERATURE VALID OOZ THU 08 JAN l 987z amp us nsn nr taMERtS minusum ussaxxems 9 850MB 0030 sis 2 850 Millibarf HectoPascal Analv Figure 8 1 x 38H g Vm w a I 6 n A D DSZL 1 0882 r 1 mg 98 fegfg Vm 08 bnq 03 2va new 6 V aquot yF M 6 9 I15 DEPT BF EQHHZRCS nuaawsmczr N SHIMGYBH Figure 83 700 Milliban HectoPascal Analysis 6661 mqwaosq OI398 738 52639 I I6 5 7 19 396 x 356 35 QZESS 22 72 i M h 16 559A v 9 aqaizy 1x 35348 08 3 I 1 5 3 g I 19662 19 563 quot7 9 564 M EL gt 1 396 i 39 39 39 PERATURE VALID 002 THU 08 JAN 1998 Figure 84 500 MillibarHectoPascal Analysis ltf 5 A 41 us39nzpr or format nueamusmzsr wasmunou 666I leqweoea Figure 85 300 Milliban ectoPascal Analysis 6 M M 3 p 6661 wqwaoaq ZI398 JAN Figure 86 250 MillibarHectoPascaI Analysis 6 us pm as nuanxnusxnrzp 6661 wqwaoaq December 1999 Section 9 COMPOSITE MOISTURE STABILITY CHART The composite moisture stability chart Figure 91 is a chart composed of four panels which depict stability precipitable water freezing level and average relative humidity conditions This computer generated chart contains information obtained from upperair observation data and is available twice daily with valid times of 00Z and 12Z The availability of upperair data for analysis on all panels is indicated by the shape of the station symbols Use the legend on the precipitable water panel Figure 93 for the explanation of symbols common to all four panels Mandatory levels referred to in the legend are the routinely used levels of surface 1000 92539 85039 70039 and 500 mb hPa Signi cant levels are nonroutine levels at which signi cant changes occur in the vertical pro le of atmospheric properties during each observation STABILITY PANEL The stability panel Figure 92 is the upper left panel of the composite moisture stability chart This panel contains two indexes that characterize the moisture and stability of the air These indexes are the K index KI and the lifted index LI K INDEX KI The K index KI provides moisture and stability information KI values range from high positive values to low negative values A high positive KI implies moist and unstable air A low or negative KI implies dry and stable air KIs are considered high when values are at and above 20 and low when values are less than 20 The KI is calculated by the summation of three terms KI 850 mbhPa temp 500 mbhPa temp 850 MbhPa dew point 700 mbhPa temp dew point spread The rst term 850 mbhPa temp 500 mbhPa temp describes the vertical temperature pro le The term compares the temperature at about 5000 feet mean sea level MSL with the temperature at about 18000 feet MSL The larger the temperature difference the less stable the air and the higher the KI The smaller the temperature difference the more stable the air and the lower the KI The second term 850 mb hPa dew point is a measure of the quantity of lowlevel moisture The higher the dew point the higher the moisture and the higher the KI The lower the dew point the lower the moisture and the lower the KI The third term 700 mb hPa temp dew point spread is a measure of the level of saturation at 700 mb hPa The smaller the spread the higher the level of saturation and the higher the KI The greater the spread the lower the level of saturation drier air and the lower the KI The KI can change signi cantly over a short time period of time due to temperature and moisture changes December 1999 LIFTED INDEX LI The lifted index LI is a common measure of atmospheric stability The LI is obtained by hypothetically displacing a surface parcel upward to 500 mb hPa about 18000 feet MSL and evaluating its stability at that level A surface parcel is a small sample of air with representative surface temperature and moisture conditions As the parcel is quotliftedquot it cools due to expansion The temperature the parcel would have at 500 mb hPa is then subtracted from the actual observed 500 mb hPa temperature This difference is the LI LI values can be positive negative or zero The LI does not identify the parcel s stability behavior at any of the intermediate altitudes between the surface and 500 mb hPa A positive LI means a lifted surface parcel of air is stable With a positive LI the parcel would be colder and more dense than the surrounding air at 500 mb hPa A more dense parcel would resist upward motion The stable surface parcel is like a rock at the bottom of a pool which being more dense than the water would resist being displaced upward The more positive the LI the more stable the air Large positive values 8 or greater would indicate very stable air A negative LI means a lifted surface parcel of air is unstable With a negative LI the parcel would be warmer and less dense than the surrounding air at 500 mb hPa A parcel which is less dense than the surrounding air would continue to rise and possibly gain increasing upward speed until stabilizing at some higher altitude The unstable surface parcel is like a cork at the bottom of a pool which being less dense than the water would accelerate upward to the surface of the pool Large negative values 6 or less would indicate very unstable air A zero LI means a lifted surface parcel of air is neutrally stable With a zero LI the lifted parcel would have the same temperature and density as the air at 500 mb hPa and have a tendency to neither rise or sink A neutrally stable parcel offers no resistance to vertical motion and without further in uence would remain at the displaced level Temperature and moisture changes in the atmosphere change lifted index values LIs decrease become less stable by increasing the surface temperatures increasing surface dew points moisture and or decreasing 500 mb hPa temperatures Cold lows and troughs aloft with warm humid surface conditions tend to be associated with unstable air LIs increase become more stable by decreasing surface temperatures decreasing surface dew points andor increasing 500 mb hPa temperatures Warm highs and ridges aloft with cool dry surface conditions tend to be associated with stable air Note that the LI can change considerably just by daytime heating and nighttime cooling of surface air Daytime heating will decrease the LI and nighttime cooling will increase the LI PLOTTED DATA Figure 92 shows the two stability indexes that are computed for each upperair station The LI is plotted above the station symbol and the KI is plotted below the symbol Station circles are blackened for LI values of zero or less An quotMquot indicates the value is missing STABILITY ANALYSIS The analysis is based on the LI only and highlights weakly stable and unstable areas Solid lines are drawn for values of 4 and less at intervals of 4 4 0 4 8 etc December 1999 USING THE PANEL The KI and LI can be used in combination to assess moisture and stability properties of air masses Air masses can be classi ed as moist and stable moist and unstable dry and stable and dry and unstable When used in combination the K1 although containing stability information is used primarily to classify moisture information and the L1 primarily to classify stability information See Figure 92 Aberdeen SD has air characterized as dry and stable The K1 is 3 dry and the L1 is 19 stable Melbourne FL is an example of dry and unstable air The K1 is 8 dry and the L1 is l unstable Moist and unstable air is depicted at Key West FL The K1 is 29 moist and the L1 is 3 unstable The last example Albany NY indicates moist and stable air The K1 is 31 moist and the L1 is 15 stable Moisture and stability properties of air masses characterize the weather High KIs are associated with the potential for clouds and precipitation Weather associated with high Us and stable air are stratiform clouds and steady precipitation Weather associated with low and negative US are unstable air convective clouds and showery precipitation The KI and LI can also be used to evaluate thunderstorm information The K1 is an indicator of the probability of thunderstorms Table 91 Higher KIs imply higher probabilities Lower KIs imply lower probabilities The low and negative LIs are indicators of intensities of thunderstorms if they occur Higher negative LIs imply greater instability and stronger updrafts in thunderstorms High positive LIs suggest little if any chance of thunderstorms Air masses classi ed with negative LIs do not always contain thunderstorms This can occur for several reasons Thunderstorm development is inhibited when a layer of stable air is located between the surface and 500 mb hPa This stable layer is referred to as a quotcapquot Inadequate amounts of moisture may also limit thunderstorm development in the presence of negative US It is also possible to have a positive LI and still have thunderstorms develop This can happen when a layer of air aloft located above stable surface air such as above a front is unstable and is sufficiently lifted or if temperature and moisture conditions change rapidly and stabilities decrease Seasons affect the use of the K1 regarding thunderstorm information During the warmer seasons of spring summer and fall a high KI generally indicates conditions are favorable for thunderstorms Table 91 During winter with cold temperatures fairly high values do not necessarily mean conditions are favorable for thunderstorms Cold 850 mb hPa temperatures mean low dew points low moisture The temperature profile term can generate high KI values but low dew points may mean inadequate moisture to support thunderstorm development December 1999 Table 9 1 Thunderstorm Potential Thunderstorm Lifted Index LI Severe Potential K Index KI Probability lt 15 near 000 0 to 2 Weak 15 19 20 20 25 21 40 2 to 6 Moderate 26 30 41 60 31 35 61 80 j 6 Strong 36 40 81 90 gt 40 near 100 o PRECIPITABLE WATER PANEL The precipitable water panel Figure 93 is the upper right panel of the composite moisture stability chart This panel is an analysis of the quantity of water vapor in the atmosphere from the surface to the 500 mb hPa level 18000 feet MSL The quantity of water vapor is shown as precipitable water which is the amount of liquid water that would result if all the water vapor were condensed Two constant factors affect precipitable water reports Warm air is capable of holding higher quantities of water vapor than cold air Therefore warm air masses generally have more precipitable water than cold air masses For example precipitable water values are higher during summer months than during winter months Also high elevation stations have smaller vertical columns of air between surface and 500 mb hPa than low elevation stations Therefore higher elevation stations tend to have lower precipitable water than lower stations December 1999 PLOTTED DATA Precipitable water values are plotted above each station symbol to the nearest hundredth of an inch The percent relative to normal for the month is plotted below the station symbol Blackened circles indicate stations with precipitable water values of 100 inch or more An M plotted above the station symbol indicates missing data ANALYSIS Isopleths lines of equal values of precipitable water are drawn and labeled for every 025 inches with heavier isopleths drawn at 050inch intervals USING THE CHART This panel is used to determine the quantity of water vapor in the air between the surface and 500 mb hPa 18000 feet MSL Higher moisture content indicates more fuel for convective conditions In Figure 93 Glasgow MT has a plot of 22100 This indicates that 22 hundreds of an inch of precipitable water is present which is the average for the month At Oklahoma City OK the 72196 indicates that 72 hundredths of an inch of precipitable water is present which is 196 percent of normal about double for any day during this month At Aberdeen SD the percent of normal value is not plotted due to insuf cient climatological data FREEZING LEVEL PANEL The freezing level panel Figure 94 is the lower left panel of the composite moisture stability chart This panel is an analysis of observed freezing levels The freezing level is the height above MSL at which the temperature is zero degrees Celsius Freezing levels are affected by air mass temperatures Colder air masses have lower freezing levels and warmer air masses have higher freezing levels Freezing levels change with the movement of contrasting cold and warm air masses For example freezing levels tend to lower behind cold fronts and rise ahead of warm fronts Generally a station has one freezing level Relative to the freezing level the lower levels have above freezing temperatures and the upper levels have belowfreezing temperatures During very cold periods all temperatures over a station may be below freezing and there would be no freezing level During colder periods of the year and with certain weather systems such as fronts stations may have more than one freezing level There would be several layers of air with alternating abovefreezing and belowfreezing temperatures A report from such a station would contain multiple freezing levels Table 92 illustrates a vertical temperature pro le drawn relative to zero degrees Celsius which contains multiple freezing levels In this table there are two layers with abovefreezing temperatures and two layers with belowfreezing temperatures Abovefreezing layers extend from the surface to 3000 feet MSL and from 6000 to 9000 feet MSL Belowfreezing layers extend from 3000 to 6000 feet MSL and above 9000 feet MSL December 1999 Table 9 2 Vertical Temperature Pro le with Freezing Levels Height O Plotted Data 9000 Feet MSL 6000 Feet MSL 3000 Feet MSL December 1999 PLOTTED DATA Observed freezing levels are plotted on the chart in hundreds of feet MSL Multiple freezing level events have plots for each freezing level BF is plotted on the chart to indicate belowfreezing temperatures at the surface quotMquot indicates missing data Note in Table 92 the freezing level plots associated with the illustrated vertical temperature pro le Table 93 provides examples of several station plots for various types of freezing level conditions ANALYSIS Freezing levels are analyzed with contours lines of constant height and are drawn as solid lines The lines are drawn with intervals of 4000 feet beginning with 4000 feet Multiple freezing levels are analyzed for the lowest freezing level Contours are labeled in hundreds of feet MSL The surface freezing level is drawn and labeled as the 32degree Fahrenheit 0 Cisotherm The surface freezing level line encloses stations with BF data plots USING THE PANEL The freezing level chart is used to assess freezing level heights and their values relative to ight profiles In Figure 94 Salt Lake City UT is an example where all temperatures above the station were below freezing below 0 C or 32 F Lake Charles LA depicts a single freezing level at 11500 feet MSL North Platte NE is an example of multiple freezing levels The temperatures were below freezing at the surface but warmed to above freezing between 4400 and 6100 feet MSL Above 6100 feet MSL the temperatures were again below freezing In areas with single freezing levels ights above the freezing level will be in belowfreezing temperatures and ights below the freezing level will be in abovefreezing temperatures In areas with multiple freezing levels there are multiple layers of above and belowfreezing temperatures According to Figure 94 a ight en route from Seattle WA to Portland OR at 7000 feet would be ying above the freezing level and in belowfreezing temperatures A ight en route at 7000 feet from Atlanta GA to Washington DC would be ying below the freezing level and in abovefreezing temperatures Special care must be exercised to properly identify the altitudes of layers with above and below freezing temperatures when there is a potential for icing conditions December 1999 Table 9 3 Plotting Freezing Levels Plotted Interpretation 0 Entire observation is below freezing 0 degrees Celsius BF Freezing level is at 2800 feet MSL temperatures below freezing above 2800 feet MSL All significant levels are missing 120 Freezing level at 12000 feet temperatures above 12000 feet are below freezing Some mandatory levels are missing 110 Temperatures are below freezing from the surface to 51 5100 feet above freezing from 5100 to 11000 feet MSL O and below freezing above 11000 feet MSL BF 90 Lowest freezing level is at 300 feet below freezing from 34 300 feet to 3400 feet above freezing from 3400 to 9000 0 feet and below freezing above 9000 feet 3 Oz Data is missing December 1999 AVERAGE RELATIVE HUMIDITY PANEL The average relative humidity panel Figure 95 is the lower right panel of the composite moisture stability chart This panel is an analysis of the average relative humidity for the layer surface to 500 mb hPa Relative humidity is the ratio of the quantity of water vapor in a sample of air compared to the air s capacity to hold water vapor expressed in percent The air s capacity to hold water vapor depends primarily on its temperature and to a lesser extent its pressure Warm air can hold more water vapor than cold air Air at lower pressure can hold more water vapor than air at higher pressure Average relative humidities of the layer are changed primarily by vertical motion of air Upward motion increases relative humidities and downward motion decreases relative humidities Relative humidity is an indicator of the degree to which air is saturated Air is saturated when it contains all of the water vapor it can hold High relative humidities moist air identify air which is at or close to saturation Air with high relative humidites often contain clouds and may produce precipitation Low relative humidities dry air identify air that is not close to saturation Low relative humidity air tends to be free of clouds PLOTTED DATA The average relative humidity is plotted above each station symbol Blackened circles indicate stations with humidities of 50 percent and higher An M indicates the value is missing ANALYSIS Isopleths of relative humidity called isohumes are drawn and labeled every 10 percent with more heavily shaded isohumes drawn for values of 10 50 and 90 percent USING THE PANEL This panel is used to determine the average relative humidity of air from the surface to 500 mb hPa Areas with high average relative humidities have a higher probability of thick clouds and possibly precipitation Areas with low average relative humidities have a lower probability of thick clouds although shallow cloud layers may be present Weatherproducing systems such as lows and fronts which are moving into areas with high average relative humidities have a high probability of developing clouds and precipitation Signi cant values of average relative humidities which support the possibility of developing clouds and precipitation are 50 and higher with unstable air and 70 and higher for stable air Weatherproducing systems affecting areas with low average relative humidities 30 and less may produce only a few clouds if any According to Figure 95 much of Arkansas has very moist air with average relative humidities greater than 90 while western Arizona has dry air with average relative humidities less than 30 High values of relative humidity do not necessarily mean high values of water vapor content precipitable water For example in Figure 93 Oakland CA had less water vapor content than Miami FL 64 and 143 respectively However in Figure 95 the average relative humidities are the same for both stations If rain were falling at both stations the result would likely be lighter precipitation totals for Oakland December 1999 USING THE CHART This chart is used to identify the distribution of moisture stability and freezing level properties of the atmosphere These properties and their association with weather systems provide important insights into existing and forecast weather conditions as well as possible aviation weather hazards Generally these properties tend to move with the associated weather systems such as lows highs and fronts Contrasting property values within weather systems are redistributed relative to the systems by advecting winds Also changes in property values relative to the systems can occur as a result of development and dissipation processes In some instances property values will remain stationary relative to geographical features such as mountains and coastal regions 1396 FREEZING LEVEL aNaLVSIS 122 use 0 MN 199 4 29 LIFTED INDEX 1142 i 7 3 3 QLL mama ts 1 ss 15 v a sum nannyng iEgELs ms 1M i 13 8 K m 7 2 sums HQNB n sieLEust ms 5 4 PRECIPITA g ii K INDEX 1 12 5 7 J 19E87m my 3411 PERCENT 18 5 f W us am or mm s LIFTED muzx aanvsxs 122 can a m 1993619 insastmczouns mm PRECIPITRBLE mum mavens 122 us a Jan 1998 4 a 6 an an C i i 5 E f t 1 i 539 0223 p V TREEgRIG LEVEL lt X71 izuoz sh g fn dgj a AF JFK 61 AyERAgg LA HUMI is an 10 nvs SFEYBSDGHE RanLvSIS Figure 91 Composite Moisture Stability Chart 122 um 07 mm 1998 6661 wqwaoaq ZI396 LIFTED INDEX 12uuz LIED n J N 1 1 K INDEX A A 8 39 us um nr cum N100 0181 LIFTED INDEX RNRLVSIS 122 NED U JRN 1998MB V NnaaNwschr wasl Figure 92 Stability Panel 6661 mlwma 81396 LL SI 1 SOME R BMW ONE H I 12002 NED UJhN1 G 7 7 HIS ING I 8 SS N L ELS ND ND S G LEVELS HIS ING 8 3 7 PRECIPITABLE wATERIEE 1 w PrERCENT OF NORMAL 2 u 2 Emu PRECIPITRBLE HRTER RNRLVSIS 12Z NED U JRN 1998 Figure 93 Precipitable Water Panel 6661 mlwma 71396 1 5 REEERIG LEVEL Lazr am an 1 F AAF N1uu 0181 FREEZING LEVEL aNaLVSIS 122 MED D7 JaN 1998 Figure 94 Freezing Level Panel 6661 mlwma 91396 7D 1 o 6 in 3 5 3 HUMIDITY SFE TD 500MB 339 3 AVERAE E RELA 7 E 85w QVG SFET SDDMB RaNaLVSIS 122 MED D7 JaN 1998 Figure 95 Average Relative Humidity Panel 6661 mlwma December 1999 Section 10 WINDS AND TEMPERATURES ALOFT CHARTS Winds aloft charts both forecast and observed are computergenerated products The forecast winds aloft charts also contain forecast temperatures aloft FORECAST WINDS AND TEMPERATURES ALOFT gFDL Forecast winds and temperatures aloft FD charts are prepared for eight levels on eight separate panels The levels are 6000 9000 12000 18000 24000 30000 34000 and 39000 feet MSL They are available daily and the 12hour progs are valid at 1200Z and 0000Z A legend on each panel shows the valid time and the level of the panel Levels below 18000 feet are in true altitude and levels 18000 feet and above are in pressure altitude Figure 101 shows examples from a winds and temperatures aloft forecast chart Figure 102 provides a closer view of the winds and temperature aloft forecast chart Temperature is in whole degrees Celsius for each forecast point and is entered above and to the right of the station circle Arrows with pennants and barbs similar to those used on the surface map show wind direction and speed Wind direction is drawn to the nearest 10 degrees with the second digit of the coded direction entered at the outer end of the arrow To determine wind direction obtain the general direction from the arrow and then use the digit to determine the direction to the nearest 10 degrees For example a wind in the northwest quadrant with a digit of 3 indicates 330 degrees A calm or light and variable wind is shown by 99 entered to the lower left of the station circle See Table 101 for examples of plotted temperatures and winds with their interpretations December 1999 Table 101 Plotted Winds and Temperatures Plotted Interpretation 12 degrees Celsius wind 060 degrees 6 1 at 5 knots 3 degrees Celsius wind 160 degrees at 25 knots 6 0 0 degrees Celsius wind 250 degrees Q at 15 knots 5 9 degrees Celsius wind 260 degrees at 50 knots 6 6 47 degrees Celsius wind 360 degrees at 115 knots 47 11 11 degrees Celsius wind calm or light and variable 99 December 1999 OBSERVED WINDS ALOFT Charts of observed winds for selected levels are sent twice daily on a fourpanel chart valid at 1200Z and 0000Z The chart depicts winds and temperatures at the second standard level 14000 24000 and 34000 feet Figure 103 is an example of this chart and Figure 104 is an example of one of the panels Wind direction and speed are shown by arrows the same as on the forecast charts A calm or light and variable wind is shown as LV and a missing wind as M both plotted to the lower right of the station circle The station circle is filled in when the reported temperaturedew point spread is 5 degrees Celsius or less Observed temperatures are included on the upper two panels of this chart 24000 feet and 34000 feet A dotted bracket around the temperature means a calculated temperature The second standard level Figure 103 for a reporting station is found between 1000 and 2000 feet above the surface depending on the station elevation The second standard level is used to determine lowlevel wind shear and frictional effects on lower atmosphere winds To compute the second standard level nd the next thousandfoot level above the station elevation and add 1000 feet to that level For example the next thousandfoot level above Oklahoma City OK station elevation 1290 feet MSL is 2000 feet MSL The second standard level for Oklahoma City OK 2000 feet 1000 feet is 3000 feet MSL or 1710 feet AGL For example Station Amarillo TX Bismarck ND Topeka KS Key West FL Station elevation 3604 MSL 1677 MSL 879 MSL 0 MSL Next thousandfoot level above station 4000 MSL 2000 MSL 1000 MSL 1000 MSL 1000 1000 1000 1000 Second standard level 5000 MSL 3000 MSL 2000 MSL 2000 MSL or or or or 1396 AGL 1323 AGL 1121 AGL 2000 AGL Note that the 12000 foot MSL panel is true altitude while the 24000 and 34000 feet MSL panels are in pressure altitude See Figure 101 USING THE CHARTS The use of the winds aloft chart is to determine winds at a proposed ight altitude or to select the best altitude for a proposed ight Temperatures also can be determined from the forecast charts Interpolation must be used to determine winds and temperatures at a level between charts and data when the time period is other than the valid time of the chart December 1999 Forecast winds are generally preferable to observed winds since they are more relevant to ight time Although observed winds are 5 to 8 hours old when received they still can be a useful reference to check for gross errors on the 12hour prog INTERNATIONAL FLIGHTS Computergenerated forecast charts of winds and temperatures aloft are available for international ights at speci ed levels The US National Centers of Environmental Prediction NCEP near Washington DC is a component of the World Area Forecast System WAF S NCEP is designated in the WAF S as both a World Area Forecast Center and a Regional Area Forecast Center RAF C Its main function as a World Area Forecast Center is to prepare global forecasts in gridpoint form of upper winds and upper air temperatures and to supply the forecasts to associated RAFCs One of NCEP s main RAFC functions is to prepare and supply to users charts of forecast winds temperatures and signi cant weather For example Figures 105 and 106 are originated by NCEP The ight level of Figure 105 is 34000 feet MSL and Figure 106 is 45000 feet MSL This along with the valid time of the chart and the data base time data from which the forecast was derived makes up the legend along an edge of each chart Forecast winds are expressed in knots for spot locations with directions and speed depicted in the same manner as the US forecast winds and temperatures aloft chart Figure 101 Forecast temperatures are depicted for spot locations inside circles that are expressed in degrees Celsius For charts with ight levels FL at or below FL180 18000 feet temperatures are depicted as negative or positive On charts for FLs above FL180 temperatures are always negative and no sign is depicted December 1999 quot4 are Imps m m a we I Ragga 25 I 23 3 39 3 Q as 354 D 93 1m triage mu me mm M 3 as ms 122 m m 519 m 1 V 571 5 I 9 5A 3 K ae z mr w 3 was 122 M J a 12 m i 1239 05 12m W592 my pm m9 m an a u 3932 M Canaan mamasgm ssmmu I 7 Figure 101 Forecast Winds and Temperatures Aloft Chart 105 106 Figure 102 Panels from r y x x W Forecast Windra and Temperatures Alo Chan December 1999 December 1999 3911qu 301V semmledulel p112 spugm pauesqo 01 9mg 1 390va 44019 mm 50an 516mm NAH mam an axansmuuun a 1 53W WM W ZVLCI 901M 35m A W W m 31 m in nunsquot a I SUNIH 314099 39 L aw L var man m 39sau 39530 1501 5pm ass 3mm mt aumums a I A x 5 am A W mu m 39sau 1 sdwax aw sum1 madam NM 4 1 314092 ld 00078 6 1 am L var man m 55 A swoon 1 13 0007 107 December 1999 sewn an sum1 madam NAH was new sumwdwu rm 51mm Imusqo um sued 1701 mm swoon 1 15 0007 f L 4 1 mm Nurman 2m 3955s 53 f 4 December 1999 Section 11 SIGNIFICANT WEATHER PROGNOSTIC CHARTS Signi cant weather prognostic charts progs Figure 111 portray forecasts of selected weather conditions at specified valid times Each valid time is the time at which the forecast conditions are expected to occur Forecasts are made from a comprehensive set of observed weather conditions The observed conditions are extended forward in time and become forecasts by considering atmospheric and environmental processes Forecasts are made for various periods of time A 12hour prog is a forecast of conditions which has a valid time 12 hours after the observed data base time thus a 12hour forecast A 24hour prog is a 24hour forecast and so on For example a 12hour forecast based on 00Z observations is valid at 12Z Altitude information on the prog charts is referenced to mean sea level MSL and compatible with aviation Altitudes below 18000 feet are true altitudes while above 18000 feet are pressure altitudes or ight levels FL The prog charts for the conterminous United States are generated for two general time periods Day 1 progs are forecasts for the rst 24hour period Day 2 progs are forecasts for the second 24hour period Day 1 prog charts are prepared for two altitude references in the atmosphere Forecast information for the surface to 24000 feet is provided by the low level signi cant weather prog chart Forecast information from above 24000 to 60000 feet is provided by the highlevel significant weather prog chart The day 2 prog chart is prepared without regard to altitude and is provided by the 36 and 48hour surface pro g chart U S LOW LEVEL SIGNIFICANT WEATHER g SIG WX PROG The lowlevel significant weather prog chart Figure 111 is a day 1 forecast of signi cant weather for the conterminous United States Weather information provided pertains to the layer from surface to FL240 400 mbs The information is provided for two forecast periods 12 hours and 24 hours The chart is composed of four panels The two lower panels depict the 12 and 24hour surface progs that are produced at Hydrometeorolgical Prediction Center HPC in Camp Springs Maryland The two upper panels depict the 12 and 24hour signi cant weather pro gs that are produced at the Aviation Weather Center AWC in Kansas City Missouri The chart is issued four times a day39 and the observation data base times for each issuance are 00Z 06Z 12Z and 18Z SURFACE PROG PANELS The surface prog panels display forecast positions and characteristics of pressure systems fronts and precipitation Surface Pressure Systems Surface pressure systems are depicted by pressure centers troughs and on selected panels isobars High and low pressure centers are identified by quotHsquot and quotLsquot respectively The central pressure of each center is speci ed Pressure troughs are identi ed by long dashed lines and labeled quotTROFquot Isobars are shown on selected panels Isobars are drawn as solid lines and portray pressure patterns The value of each isobar is identi ed by a twodigit code placed on each isobar Isobars are drawn with intervals of 8 mbs relative to the 1000 mb isobar Note that this interval is larger than the 4mb interval used on the surface analysis chart The 8mb interval provides a less sensitive analysis of pressure patterns than the 4mb interval Occasionally nonstandard isobars will be drawn using 4mb intervals to highlight patterns with weak pressure gradients Nonstandard isobars are drawn as dashed lines Examples of standard isobars drawn are the 992 1000 and 1008 mb isobars December 1999 Fronts Surface fronts are depicted on each panel Formats used are the standard symbols and threedigit characterization code used on the surface analysis chart See Section 5 Precipitation Solid lines enclose precipitation areas Symbols specify the forms and types of precipitation See Table 111 A mix of precipitation is indicated by the use of two pertinent symbols separated by a slash Identifying symbols are positioned within or adjacent to the precipitation areas Precipitation conditions are described further by the use of shading Stable precipitation events are classi ed as continuous or intermittent Continuous precipitation is a dominant and widespread event and therefore shaded Intermittent precipitation is a periodic and patchy event and unshaded Shading is also used to characterize the coverage of unstable precipitation events Areas with more than half coverage are shaded and half or less coverage are unshaded See Table 112 A bold dashed line is used to separate precipitation with contrasting characteristics within an outlined area For example a dashed line would be used to separate an area of snow from an area of rain Table 11 1 Standard Weather Symbols December 1999 A Moder ate turbulence A Severe turbulence w Moderate icing W Severe icing Rain X Snow 9 Drizzle lt0 7 E 39n shower ltgtK Snow Shower N Thunderstorm 392 Freezing rain Q Tropical storm Hurricane Typhoon Decerrbex 19w mumm nlrw aqu Iain scmncANerA39nIm mus m yn cam wallan my dls ay necast wratth ylrg camganzs fnenrg 1mg ard n unlmce funk layxsun39ace m mm A lzgendan m chm mum 5mm andcmzm usedfm Lhasa summons 52 Figure m Wm Flying Catngnr39n m wzathx ymg camganzs m vlsml mgm nllzs vm marme m MVFR and mm mgm ndzs mo Ceiling mawamnymm usedfm each camgaxym m m as usedfm m wzadnzxdzpl tmnchm 5quot 52mm 6 1m mas a emlnsedbysnhdhms MVFR mas m enclasedbyscallnpdhms A mth mas m m Flun39lg ma December 1999 intersection of the surface freezing level line and freezing level contours encloses an area with surface based multiple freezing levels Turbulence Areas of moderate or greater turbulence are enclosed by bold long dashed lines Turbulence intensities are identi ed by symbols The vertical extent of turbulence layers is specified by top and base heights in hundreds of feet Height values are relative to MSL with the top and base heights separated by a line A top height of quot240quot indicates turbulence at or above 24000 feet The upper limit of the prog is 24000 feet The base height is omitted where turbulence reaches the surface For example quot080 quot identi es a turbulence layer from the surface to 8000 feet MSL Thunderstorms always imply a variety of hazardous conditions to aviation including moderate or greater turbulence Generally turbulence conditions implied with thunderstorms is not depicted on the chart However for added emphasis moderate to severe turbulence surface to above 24000 feet is depicted for areas that have thunderstorms with more than half coverage on the surface prog Intensity symbols and layer altitudes appear within or adjacent to the forecast area USING THE CHART The lowlevel significant weather prog chart provides an overview of selected ying weather conditions up to 24000 feet for day 1 Much insight can be gained by evaluating the individual elds of pressure patterns fronts precipitation weather ying categories freezing levels and turbulence displayed on the chart In addition certain inferences can be made from the chart Surface winds can be inferred from surface pressure patterns Structural icing can be inferred in areas which have clouds and precipitation above freezing levels and in areas of freezing precipitation The lowlevel prog chart can also be used to obtain an overview of the progression of weather during day l The progression of weather is the change in position size and intensity of weather with time Progression analysis is accomplished by comparing charts of observed conditions with the 12 and 24hour prog panels Progression analysis adds insight to the timecontinuity of the weather from before ight time to after ight time The lowlevel prog chart makes the comprehension of weather details easier and more meaningful A comprehensive overview of weather conditions does not provide sufficient information for ight planning Additional weather details are required Essential weather details are provided by observed reports forecast products and weather advisories Weather details are often numerous An effective overview of observed and prog charts allows the many essential details to t into place and have continuity 36 AND 48 HOUR SURFACE PROG The 36 and 48hour surface prog chart Figure 112 is a day 2 forecast of general weather for the conterminous United States The chart is an extension of the day 1 US lowlevel significant weather prog chart issued from the same observed data base time These two prog charts make up a forecast package The chart is issued twice daily The observation data base times for each issuance are 00Z and l2Z For example a chart issued based on 00Z Tuesday observations has a 36hour valid time of l2Z Wednesday and a 48hour valid time of 00Z Thursday The chart is composed of two panels and a forecast discussion The two panels contain the 36 and 48hour surface progs SURFACE PROG PANELS The surface prog panels display forecast positions and characteristics of pressure patterns fronts and precipitation December 1999 Surface Pressure Systems Surface pressure systems are depicted by pressure centers troughs and isobars Formats used for each feature are the same as used for the surface prog panels of the US lowlevel signi cant weather prog chart Fronts Surface fronts are depicted by using the standard symbols and threedigit characterization code used on the surface analysis chart See Section 5 Precipitation Precipitation areas are outlined on each panel Formats used to locate and characterize precipitation are the same as used for the surface prog panels of the US lowlevel prog chart FORECAST DISCUSSION The forecast discussion is a discussion of the day l and day 2 forecast package The discussion will include identi cation and characterization of weather systems and associated weather conditions portrayed on the prog charts USING THE CHART The 36 and 48hour surface pro g chart provides an outlook of general weather conditions for day 2 The 36 and 48hour prog can also be used to assess the progression of weather through day 2 HIGH LEVEL SIGNIFICANT WEATHER PROG The highlevel signi cant weather prog Figures 113 and 114 is a day l forecast of signi cant weather Weather information provided pertains to the layer from above 24000 to 60000 feet FL25 0FL600 The pro g covers a large portion of the Northern Hemisphere and a limited portion of the Southern Hemisphere Coverage ranges from the eastern Asiatic coast eastward across the Paci c North America and the Atlantic into Europe and northwestern Africa The prog extends southward into northern South America The area covered by the prog is divided into sections Each section covers a part of the forecast area Some sections overlap The various sections are formatted on polar or Mercator projection background maps and issued as charts Each pro g chart is issued four times a day The valid times are 00Z 06Z l2Z and 18Z Conditions routinely appearing on the chart are jet streams cumulonimbus clouds turbulence and tropopause heights Surface fronts are also included to add perspective Other conditions will appear on the chart as pertinent They are tropical cyclones squall lines volcanic eruption sites and sandstorms and dust storms December 1999 Jet Streams Jet streams with a maximum Speed of more than 80 knots are identi ed by bold lineS Jet stream lineS lie along the core of maximum windS Arrowheads on the lineS indicate the orientation of each jet stream Double hatched lineS positioned along the jet core identify changes of wind Speed These Speed indicators are drawn at 20knot intervals and begin with 100 knots Wind Speed maximums along the jet core are characterized by wind symbols and altitudes A standard wind symbol Shaft pennants and barbs is placed at each pertinent position to identify velocity The altitude in hundreds of feet prefaced with quotFLquot is placed adjacent to each wind symbol Example Cumulonimbus Clouds Cumulonimbus clouds CBS are thunderstorm clouds Areas of CBS meeting select criteria are enclosed by scalloped lineS The criteria are wideSpread CBS within an area or along a line with little or no Space between individual cloudS and CBS are embedded in cloud layerS or concealed by haze or dust The prog doeS not diSplay isolated or scattered CBS onehalf or leSS coverage which are not embedded in cloudS haze or dust Cumulonimbus areaS are identified with quotCBquot and characterized by coverage and topS Coverages are identi ed aS isolated ISOL occaSional OCNL and frequent FRQ Isolated and occaSional CBS are further characterized aS embedded EMBD Coverage valueS for the identifiers are isolated leSS than 18 occaSional 18 to 48 and frequent more than 48 TopS are identi ed in hundredS of feet uSing the standard top and base format BaseS extend below 24000 feet below the prog S forecast layer and are encoded quotXXXquot The identi cation and characterization of each cumulonimbus area will appear within or adjacent to the outlined area Thunderstorms alwayS imply a variety of aviation hazardS including moderate or greater turbulence and hail Examples ISOL EMBD CB OCNL EMBD CB XXX XXX Turbulence AreaS of moderate or greater turbulence are enclosed by bold daShed lineS Turbulence conditionS identified are those associated with wind Shear zoneS and mountain waveS Wind Shear zoneS include Speed ShearS associated with jet streams and areaS with Sharply curved ow Turbulence associated with thunderstorms iS not identi ed Thunderstorms imply turbulence Turbulence intenSitieS are identi ed by symbolS The vertical extent of turbulence layerS iS Speci ed by top and base heightS in hundredS of feet Turbulence baseS which extendS below the layer of the chart are identi ed with quotXXXquot Top and 117 December 1999 base heights are separated by a line Height values are pressure altitudes For example quot310XXXquot identifies a layer of turbulence from below FL240 to FL310 Example J33 XXX Tropopause Heights Tropopause heights are plotted in hundreds of feet at selected locations Heights are enclosed by rectangles Centers of high and low heights are identified with quotHquot and quotLquot respectively along with their heights and enclosed by polygons Examples Surface Fronts Surface fronts are depicted on the prog to provide added perspective Symbols used are the standard symbols used on the surface analysis chart Movements of fronts are identi ed at selected positions A vector with a number plotted adjacent to the vector identi es the direction and speed of movement See Section 5 Example 15 December 1999 Tropical Cyclones The positions of hurricanes typhoons and tropical storms are depicted by symbols The only difference between the hurricanetyphoon symbol and tropical storm symbol is the circle of the hurricanetyphoon symbol is shaded in When pertinent the name of each storm is positioned adjacent to the symbol Cumulonimbus cloud activity meeting chart criteria is identi ed and characterized relative to each storm Example Tropical Storm Squall Lines Severe squall lines are lines of CBS with 58 coverage or greater Squall lines are identified by long dashed lines and each dash is separated by a quotvquot Cumulonimbus cloud activity meeting chart criteria is identified and characterized with each squall line Example V V Volcanic Eruption Sites Volcanic eruption sites are identi ed by a trapezoidal symbol The dot on the base of the trapezoid locates the latitude and longitude of the volcano The name of the volcano its latitude and its longitude are noted adjacent to the symbol Pertinent SIGMETs containing information regarding volcanic ash will be in effect Example TUNGURAHUA 15S 784w December 1999 Sandstorms and Dust Storms Areas of widespread sandstorrns and dust storms are labeled by symbol The symbol with the arrow depicts areas of widespread sandstorm or dust storm while the symbol without the arrow depicts severe sandstorm or dust haze Example USING THE CHART The highlevel sig weather prog is used to get an overview of selected ying weather conditions above 24000 feet Much insight can be gained by evaluating jet streams cumulonimbus clouds turbulence associated surface fronts signi cant tropical storm complexes including tropical cyclones squall lines sandstorms and dust storms 1110 II39II mum 5m 5 rc VT 082 THU JFIN B 138 12HR 516 NX P LON LVL SFC I mm mm n HunUR LESS mm mus Mnnmmr n nnrmw maume W wmm mu m swam VT OSZ THU JHN 8 19953 IZHR SIB NX FROG mm mva VU HLSU wk on an mm was 5w mm mm mm VT 182 THU JHN 8 19953 74HR SIB NX FROG Figure 111 US LowLevel Significant Weather Prog 6661 mqumaq ZI39II ORRVEC quot SEC PROG VII I22 SRT OS J NCEP PROGNOSTIC DISCUSSION FROH I2OOZ TNU JRN O39I Io sPRRn MIIO IOMIOMI IMRu IM CNTRL PP L CHI NS RMO IMIO IM MIO RIL RMO MERM us OM I39RI IM assoc IIIIII R LRO RRR or IIRRM ROVECIIOM PUSNING MIIO RMnO or IM nMPLIFvIMO uPsIRRM IROF R CNRNGE OVER TO R HIX BRO OF PCPN IS LIKELY RCRS NERRLV RLL OF THE NERN u s I39RI INTO sRI Rs IIRRMR RIR IIL sIRRM MIIO RIIRO Or III ISSS NVDRONE TEOROLOGICRL PREDICT ION CENTER NHS CRNP SPRINGS ND R 2 MRMunL ORRPMIcs IIIE LRIESI MOOEL RUNS RR IN GOOD RGRMMI IIIIII III OVRRLL TREND Or RMPLIFIcRIIOM IO IIIE BRORO cchOMIO FLOII RcRs III u s R uPsIRRM RMPLII39VIM I I39 RcRs III LOHER Ms V LLEVCNTR RIOO ILDS ovR IM MRM PRC Run a OOIIMSIRRM IRDF RMPLIFI consILoanLv MVV RRIM LIKELV COMI IMIO RI LERST IOMIOMI RLOMO TNE HS RLLE RE N NEVERSOHE F IRLV SOFNT DIFFS NITN THE R STN V FRONTRL DNDRV RCRS TNIS REGION FRONT L CONVECTION SNOU D DETRILS F THIS HPLIFIb TION RND THE R SOC EC FERTURES TNEN P ERD NEHO INTO THE N VRLLEV FRI INT S RS LON T NIO LEVEL PRI39 III MGMRVM sOLM IIII II I FCSIG R sLIsIIILv MDR RMPLII39IO OVMRMIcs sIRMsIIIM LONG III RI39ORMMIIOMEO Ms sIREMOIIIEM G IROF DIOGINO sIIn av nR v III I I0 IM M 1 Ms an vM M FROMI MORV cRs I E quotIO 5 I M OF IME M IIOMR REIMFORCIMO RHPLITUDE OF THE UPSTRERH NERN PRC UPR RIDGE IN DDITIONTNE ETR SNOT O RRCT IR NL CONT TO PUSN OUICKLV SND INTO THE NRN PLRIN R SLONER EIIO PUSN FROM IOMIOMI IMIO R v sRI FIDDIII MnL LIOMI SNOHS Mrquot S RR TO E H IN NS DRROCLINIC BNDRV STRENGTHENINO OV TNE ON V SE D I O E NR PL INS O SRT NE O OF R DEVELOPING RLDERTR I39RI INTO s I III e I MOR RMPLII39IO UPR IROI39 CLIPPER PUSHING sIIn RLOMG III RRcIII R MI IIx run I SNOULO RLSO SUPPORT INCRERSED POST FR NTRL PCPN DEVELOPING OV 5TB SI D S PERIOD RS SEC HIGH PRESSURE BUILOS IN RESPONSE TO THE UPSTRERH HPLIFVING RIDOE TNIS OTBRSIN SEC RIDGE NL STRENOTNEN E RLV FRI IMIs POsI FROMIRL PCPN IIL LIIltLV a CHRNGINO FROM RRIM I0 I sRMIn N 39S a Rs SRM CR av SRI IIIIM MIGM IIIMOS POSSIBLE SS B E II NGE IIH IIIIIII Inns IM III 3 IO 639 N IIHIII DIINI snous RLsO LIKELV IxPLERsE MOIxx III PC IIEB ROOREss IIRS OIIRMGEOx GRRPIIIcs RR MOII Figure 112 US LowLevel 36 and 48hour Signi cant Weather Prog 6661 mqwaoaq EI39II 39 m w GB 1H 1 L A 6 PBBE IO KHBC L Namp L R 39 39 SEVERE TURBULENCE FIND HRIL 39 FL HO H C ECK SIGMETS FDR VDLL FINIC FISH Figure 113 US HighLevel Signi cant Weather Prog 6661 Jequleoea 1713911 mw 67 S s SW7 39 PGNEfif BfI rmwqu a 39 xxx quotII I I I RN 39 L 4L nude6 S HJ 39 m w DNXXXJ I D 39 39 39 39 39 v I u a I quotnw 39 39 39 39 m u I 03w 1 also a FC NH HleIUN GNX FL 250500 V 002 FRI 10 HPR 1998 Bank HND ca IMPLY non DR ERE TURBULENCE nun HHIL CK smuns FDR VDLCHNIC HSH 6661 Jeqmeoeq December 1999 Section 12 CONVECTIVE OUTLOOK CHART The convective outlook chart Figure 121 delineates areas forecast to have thunderstorms This chart is presented in two panels The lefthand panel is the Day 1 Convective Outlook and the righthand panel is the Day 2 Convective Outlook These guidance products are produced at the Storm Prediction Center SPC in Norman OK DAY 1 CONVECTIVE OUTLOOK The Day 1 Convective Outlook Figure 121 outlines areas in the continental United States where thunderstorms are forecasted during the Day 1 period It is issued ve times daily The first issuance is 06Z and is the initial Day 1 Convective Outlook that is valid l2Z that day until l2Z the following day The other issuances are l300Z l630Z 2000Z and 0100Z and all issuances are valid until l2Z the following day The outlook issued qualifies the level of risk ie SLGT MDT PHGH as well as the areas of general thunderstorms DAY 2 CONVECTIVE OUTLOOK The Day 2 Convective Outlook contains the same information as the Day 1 Convective Outlook It is issued twice a day It is initially issued at 0830Z during standard time and 0730Z during daylight time It is updated at l730Z The timeframe covered is from l2Z the following day to l2Z the next day For example if today is Monday the Day 2 Convective Outlook will cover the period l2Z Tuesday to l2Z Wednesday The outlook issued qualifies the level of risk ie SLGT MDT PHGH as well as the areas of general thunderstorms LEVELS OF RISK Risk areas come in three varieties and are based on the expected number of severe thunderstorm reports per geographical unit and forecaster confidence Table 121 indicates the labels that appear on both the Day 1 and Day 2 Convective Outlook charts December 1999 Table 12 1 Notations ofRisk NOTATION EXPLANATION SEE TEXT Used for those situations where a SLGT risk was considered but at the time of the forecast was not warranted SLGT Slight risk A high probability of 5 to 29 reports ofl inch or larger hail andor 3 5 tornadoes andor 5 to 29 wind events or a lowmoderate probability of moderate to high risk being issued later if some conditions come together MDT Moderate risk A high probability of at least 30 reports of hail 1 inch or larger or 6 19 tornadoes or numerous wind events 30 HIGH High risk A high probability of at least 20 tornadoes with at least two of them rated F3 or higher or an extreme derecho causing widespread 50 or more wind events with numerous higher end wind 80 mph or higher and structural damage reports SEE TEXT is used for those situations where a slight risk was considered but at the time of the forecast was not warranted Although there is no severe outlook for the labeled area users should read the text of the convective outlook AC forecast message to learn more about the potential for a threat to develop if some particular conditions do come together Slight SLGT risk implies wellorganized severe thunderstorms are expected but in small numbers and or low coverage Moderate MDT risks imply a greater concentration of severe thunderstorms and in most situations greater magnitude of severe weather High IHGH risk almost always means a major severe weather outbreak is expected with great coverage of severe weather and enhanced likelihood of extreme severe events ie violent tornadoes or unusually intense damaging wind events SPC issues a public information statement PWO describing a quotparticularly dangerous situationquot when IHGH risk areas are in effect and it sometimes issues a PWO for MDT risk situations Some National Weather Service NWS of ces will include in their public forecasts the phrase quotsome thunderstorms may be severequot when a MDT or IHGH risk is issued In addition to the severe risk areas general thunderstorms nonsevere are outlined but with no label on the graphic map USING THE CHART The Day 1 and Day 2 Convective Outlooks Charts are ight planning tools used to determine forecast areas of thunderstorms DAYl CONVEC TTTTTTTT OK FROM V 00000000 I98 UNTIL IZDUZ 0443498 FORECASTER HART EEEEEEEEEEEEEEEEE OK ISSUED UUUUUUU 43998 FROM IZUUZ 0410498 UNTI 39 12002 DtlJ39IJSJ39DS L FORECASTER HART Figure 121 Severe Weather Outlook Chart 6661 mqwaoaq December 1999 Section 13 VOLCANIC ASH ADVISORY CENTER VAAC PRODUCTS The Volcanic Ash Advisory Center VAAC may issue two products when there is a volcanic eruption the Volcanic Ash Advisory Statement VAAS and forecast charts of ash dispersion The US VAACs are the AAWU in Anchorage Alaska and the Washington DC VAAC located in Camp Springs Maryland Other international centers contribute to the tracking of volcanic ash events The VAACs do not issue routine products but create and issue them when a volcanic eruption occurs The products are based on information from PIREPs MWO SIGMETs satellite observations and volcanic observatory reports Since the products are triggered by the occurrence of an eruption pilot reports concerning volcanic activity are extremely important VOLCANIC ASH ADVISORY STATEMENT gVAASL Usually the first VAAC product to be issued is the Volcanic Ash Advisory StatementVAAS The VAAS is required to be issued within 6 hours of an eruption and every 6 hours after that However it can be issued more frequently if new information about the eruption is received The VAAS summarizes the currently known information about the eruption It may include the location of the volcano height of the volcano summit height of the ash plume a latitude longitude box of the ash dispersion cloud and a forecast of ash dispersion The height of the ash cloud is estimated by meteorologists analyzing satellite imagery and satellite cloud drift winds combined with any pilot reports volcano observatory reports and upperair wind reports The VAASs are transmitted to users via the Global Telecommunications System GTS the World Area Forecast System WAF S the Aeronautical Fixed Telecommunications Network AF TN the FAA communications system WMWCR and the NWS Family of Services In addition VAASs are available on several Internet sites listed on the last page of this document December 1999 Example of a VAAS FVAK20 PANC 190323 VOLCANIC ASH ADVISORY ALERT ALASKA AVIATION WEATHER UNIT NATIONAL WEATHER SERVICE ANCHORAGE AK ISSUED 0300 UTC SUNDAY JULY 19 1998 BY ANCHORAGE VAAC VOLCANO KARYMSKY 1000 13 9801 KAMCHATKA 5405N 15943E 1486 M 4875 FT SOURCES OF INFORMATION PILOT REPORT ERUPTION DETAILS ERUPTION TO FL100 REPORTED BY PILOT REPORT AT 190200 UTC VIA WASIHNGTON DC VAAC ASH CLOUD DESCRIPTION NA ASH CLOUD TRAJECTORY NE 10 KT 12 HOUR OUTLOOK IF ASH PERSISTS ALOFT AT 12 HOURS THE FORECAST AREA FROM THE PUFF MODEL BELOW 15000FT IS 56N 161E 55N 166E 54N 165E 55N 162E ADDITIONAL INFORMATION NO ERUPTION VISIBLE ON SATELLITE IIVIAGERY DUE TO CLOUD IN AREA TIHS WILL BE THE ONLY ADVISORY ISSUED FOR TIHS EVENT DAC JUL98 AAWU VOLCANIC ASH FORECAST TRANSPORT AND DISPERSION gVAFTAD CHART The Volcanic Ash Forecast Transport and Dispersion VAF TAD Chart Figures 131 and 132 is generated by a threedimensional timedependent dispersion model developed by the National Oceanic and Atmospheric Administration NOAA Air Resources Laboratory ARL The VAF TAD model focuses on hazards to aircraft ight operations caused by a volcanic eruption with an emphasis on the ash cloud location in time and space It uses National Centers for Environmental Prediction NCEP forecast data to determine the location of ash concentrations over 6hour and 12hour intervals with valid times beginning 6 12 24 and 36 hours following a volcanic eruption This computerprepared chart is not issued on a routine basis but only as volcanic eruptions are reported Since the VAF TAD chart is triggered by the occurrence of volcanic eruption PIREPs concerning volcanic activity are very important Initial input to the VAF TAD model run and the resulting chart include geographic region volcano name volcano latitude and longitude eruption date and time and initial ash cloud height Utilizing the NCEP meteorological forecast guidance volcanic ash particle transport and dispersion are depicted horizontally and vertically through representative atmospheric layers The charts from an actual eruption will be labeled with ALERT Another possible reason to generate a chart could be for potential volcanic eruption This chart would be labeled WATCH as shown on Figure 131 132 December 1999 VAFTAD PRODUCT The VAF TAD product presents the relative concentrations of ash following a volcanic eruption for three layers of the atmosphere in addition to a composite of ash concentration through the atmosphere Atmospheric layers depicted are surface to ight level FL 200 surface to FL550 composite FL200 to FL350 and FL350 to FL550 Figure 131 shows 8 panels of ash cloud relative concentrations for 12 to 24 hours and Figure 132 shows 18 to 24 hours after a volcanic eruption Note that the rst 6 hours after the volcanic eruption are not depicted An appropriate SIGMET will be issued by an MWO for that period concerning the volcanic eruption and the area affected by the ash cloud The four panels in any column are valid for the same time interval speci ed and located below the third panel The top three panels in each column provide the ash location and relative concentrations for an atmospheric layer identi ed by top and bottom ight levels The highest layer is at the top of the chart Volcano eruption information is given in the legend at the lower left see Figure 131 which includes the volcano name with location symbol latitude and longitude eruption date and time duration and ash column height USING THE CHART The VAF TAD chart is strictly for advanced ight planning purposes It is not intended to take the place of SIGMETs regarding volcanic eruptions and ash December 1999 EU UPPER HALF 1 r lt X r 39 1 39x 1 xx 4 z x r 2 V V39 r r q v 1 x x v r I A X x x x 1 x x 5 I W x r 1 r x 1 g r 3 39 r a 1 w 39 z a l 1 r x I k v x ERLA E 17 CEWERLON 62 3 RAGEUS3CL CHART 1 RR 395 I Lye TM m A H Lgxm raj 2 I r a x r quotk C xi x x 2 x E r 1 z x x 1 7 r X r cr quotj 3 5W 1 1 xgtL N V7 gk i 1 g 39a a g x 39 J 1 RSV quota r r 2 J quotV E m r r I r r 2 J l I LWW Hr r A 1 r l 1 x r I V J 2 J I p 1 39 FL350 I pal E I r FLzoo egggggw 4 39 x quotu x r a ip a xvKM Vquot rfJ quot quot x39w 139 y 5 rlt 39 v T r a a x w a 7 M f 4 i quot 8 J 4 r4 2 LMOI U39W ZP IL x i X x s H La1quot Rik i l V 39 1 l x I wt I 39 w s Q A 4 x a 2 quot gt z quotquotx K quot1 39 A A V a a quotquotquot VJ V SURFACE e 13 x x 9 J 23 a 5 E VALID 062 24 OCT 97 ERUPTiON12H VALID 182 24 OCT 97 ERUPTION24H r quot a I x x 3 x x r x quot x u r x a q r y x x x v z x J 39 a r R 39 x 1 x r 2 x 1 x5 3 x i x u39 r r r r t quot s X x x 2 Hr i I 4 u i x 1 4 r r r v amp FL550 39 SURFACE COMPOSITE 39 CHART quot 1 a E S LOWER HALF r wE NCAAARE VOLCANEIE ASH FORE AS E TRANSPORT AND DiSPERSEON VATAD SSUED BY NWSLNCEPNCO a ESEEmERE HILLSISJN 622w AVN FcEZEc Assrogcg ViSUAL ASH CLOUD ERUPTION 182 23 OCT 97 ALERTW DURAEON 1 HR SEE QURRENT ASEi COLUMN FL4OO WATCH Figure 131 Volcanic Ash Forecast Chart 134 December 1999 ESL QERLAT 17 CEMETERLGN 62RAoausz3o r 3 a x I v C rquot y r x 1 g 7 a x x s I 7 1 K I r x v a r HR CHART 2 UPPER HALF H W T 39I Whorm a 02 r 9 5 FLsso FL350 0m HR W V l r J V r w r x V U L TquotV H x g W quot r x r r v lt H FL350 F L200 H x m M i r lt I y 4 f 39 WA r I 39 i 3 a HWJ Jae J y quot c a 2 c 3 E w 4 w 2 I d x 1 5 a 331 g H200 9 9 a e SURFACE vx lt a VALID 122 24 OCT 97 ERUPTIONHBH VALID 132 24 o T 97 ERUPTION 4 2 MW a a z c v r39 3 g a 2 it V x v 24H 1 x x x 1 x m x r 39 a 3 3 X 1 r I 39 X N 39 s v ru 1 pt 39 1 k Y LJL r I i I A H550 39 SURFACE f3 COMPOSITE r 4 Al Vn wmf 7 r M E a l W MHMA X a A 1 I k M c f Er MKJJJ Low fiism NOMARL VOLCANtC ASH FORECAST TRANSPCRT AND DEPERSEON VAFi AE I VISUAL CLOUD ERUPTEON 182 23 OCT 97 AL mi39m DURATION 1 HR WATCH SEE CURRENT S G V ET ASH COLUMN FLACO WARNING AREA Figure 132 Volcanic Ash Forecast Chart 13 5 December 1999 Section 14 TURBULENCE LOCATIONS CONVERSION AND DENSITY ALTITUDE TABLES CONTRACTION S AND ACRONYMS SCHEDULE OF PRODUCTS NATIONAL WEATHER SERVICE STATION IDENTIFIERS WSR 88D SITES AND INTERNET ADDRESSES This section provides text graphs and tables that can be used by the pilot to further understand the weather Information included covers Locations of probable turbulence Standard conversions table Density altitude and chart Contractions and acronyms Scheduled issuance and valid times of forecast products National Weather Service station identi ers and WSR88D sites Internet addresses 899P N1 LOCATIONS OF PROBABLE TURBULENCE Turbulence occurs due to either terrain features or weather phenomenon which can produce intensities from light to extreme The type and intensity of the turbulence will depend on the situations as described in the following paragraphs LIGHT TURBULEN CE Light turbulence can be caused by obstruction of the wind in hilly or mountainous terrain Even with light winds there can be enough displacement of the wind to produce smallscale eddies or turbulence Weather conditions that can cause light turbulence are associated with clearair convective currents over a heated surface or near and in small cumulus clouds Weak wind shear in the vicinity of troughs aloft lows aloft jet streams or the tropopause can cause light turbulence Also in the lower 5000 feet of the atmosphere light turbulence can occur when winds are near 15 knots or where the air is colder than the underlying surfaces MODERATE TURBULEN CE Moderate turbulence will be reported in mountainous areas with a wind component of 25 to 50 knots perpendicular to and near the level of the ridge The turbulence will be located at all levels from the surface to 5000 feet above the tropopause The areas most likely to have moderate turbulence is within 5000 feet of the ridge level at the base of relatively stable layers below the base of the tropopause or within the tropopause layer The turbulence will extend downstream from the lee of the ridge for 150 to 300 miles Also moderate turbulence can be encountered in and near towering cumuliform clouds and thunderstorms in the dissipating stage Moderate turbulence can occur in the lower 5000 feet of the troposphere when surface winds are 30 knots or more where heating of the underlying surface is unusually strong where there is an invasion of very cold air or in fronts aloft December 1999 Wind shear in the vertical direction that exceeds 6 knots per 1000 feet and or horizontal wind shear that exceeds 18 knots per 150 miles will produce moderate turbulence SEVERE TURBULEN CE Severe turbulence is likely in mountainous areas with a wind component exceeding 50 knots perpendicular to and near the level of the ridge The location of the severe turbulence will be in 5000 foot layers at and below the ridge level in rotor clouds or rotor action at the tropopause and sometimes at the base of other stable layers below the tropopause The severe turbulence will extend downstream from the lee of the ridge for 50 to 150 miles Severe turbulence can be encountered in and near growing and mature thunderstorms and occasionally in other towering cumuliform clouds Severe turbulence will also occur 50 to 100 miles on the cold side of the center of the jet stream in troughs aloft and in lows aloft where vertical wind shear exceeds 10 knots per 1000 feet and horizontal wind shear exceeds 40 knots per 150 miles EXTREME TURBULEN CE Extreme turbulence will be found in mountain wave situations The turbulence will be located in and below the level of welldeveloped rotor clouds Sometimes the turbulence extends to the ground Besides mountain wave situations extreme turbulence will occur in severe thunderstorms A severe thunderstorm is indicated by large hailstones diameter 3 inch or greater strong radar echoes or continuous lightning December 1999 STANDARD CONVERSION TABLE Speed 7 Distance Temperature Pressure 7 Almude Alllmeier Semng MH F C Masgggas 1 180 120 5 7 1107 7 7970 7 7170 0 90 7 40 7 1007 71 so 100 7980 7 7150 80 90 907 7 30 7 1 so 7990 70 20 71000 so 7100 5 0 71010 607 7 7 5 7 90 40 7 507 7 80 30 0 71020 7 40 70 7 20 40 7 60 710 7 1030 7 30 7 10 25 307 50 26 7 1040 7 7 40 720 900 ii 20 7 27 7 207 quot0 7 7 30 28 7 7 7 7 7 31 0771050 20 730 29 7 730 30 1000 7 771060 740 740 31 105077 I F C INS MBSIhPas 00395 31 57711065 INS MES IhPas 39Sandald Armnsphere Figlre 1471 Standard Conversion Table December 1999 DENSITY ALTITUDE Density altitude can affect the takeoff climb and landing performance of any aircraft The distance required to take off and land and the rate of climb are affected by density altitude Aircraft will perform better in low density altitude conditions Low density altitude conditions exist when the air is dense This occurs when the temperature is cold combined with a high pressure system The air is the most dense in this situation and the aircraft will perform as if it were at a lower altitude For example a plane is at an airport with a station elevation of 7000 feet MSL The atmospheric conditions at that airport indicate a low density altitude situation The density altitude is calculated to be 5500 feet MSL The plane will perform as if it were at 5500 feet MSL instead of 7000 feet MSL This low density altitude situation will decrease takeoff and landing roll while increasing the initial rate of climb While low density altitude increases aircraft performance high density altitude can lead to an aircraft accident High density altitude situations are more prevalent at higher elevations High temperatures combined with a low pressure system will produce a high density altitude situation The air is least dense in this situation Airports in mountainous terrain are more susceptible to high density altitude situations because they already have a high station elevation The combination of a high station elevation high temperatures and low pressure will produce a very high density altitude situation For example a plane is at an airport with a station elevation of 7000 feet MSL Using the values of station elevation temperature and pressure the density altitude is calculated to be 12000 feet MSL Any aircraft taking off or landing at that airport will perform as if it were at an airport with a station elevation of 12000 MSL For some aircraft a high density altitude situation will indicate an altitude higher than the service ceiling of that speci c aircraft In that case if a pilot attempts to take off during a high density situation the aircraft will not be able to gain altitude but stay in ground effect and possibly crash Use Figure 142 to nd density altitude either on the ground or aloft Set the aircraft s altimeter at 2992 inches The altimeter will indicate pressure altitude Read the outside air temperature Enter the graph at the pressure altitude value and move horizontally to the temperature value Read the density altitude from the sloping lines Examples Density altitude in ight Pressure altitude is 9500 feet and the temperature is 8 degrees C Find 9500 feet on the left of the chart and move to 8 degrees C Density altitude is 9000 feet See dot on the chart that is labeled number 1 Density altitude for takeoff Pressure altitude is 4950 feet and the temperature is 97 degrees F Enter the graph at 4950 feet and move across to 97 degrees F Density altitude is 8200 feet See dot on the chart that is labeled number 2 145 Figure 142 Density Altitude Computation Chart L 50 40 20 ampr 20 l 1 40 TEMPERATURE F 1 60 80 1 100 l 120 TEMPERATURE C PRESSURE ALTITUDE FEET O 20000 15 00 10000 5000 o O 5 i i quot f 4Zm I I if I I l Afyfnnll r 1 n 7934 II Iquot quotI 4 L317 I 1 1391 7325 L 37 w i 1 Arum mm H LglmzzlgWA m 0 40 30 1 20 10 i 4 0 4 10 391quotTquot fjf39 I T 20 30 47 T9quotT I DENSITY ALTITUDE T 40 O 5 9L 1 v1 4 j 50 December 1999 December 1999 CONTRACTIONS AND ACRONYMS Contractions and acronyms are used extensively in surface reports pilot reports and forecasts A AAWU 7 Alaskan Aviation Weather Unit ABNDT Abundant ABNML Abnormal AC Convective outlook or altocumulus ACC Altocumulus castellanus ACCUM Accumulate ACFT Aircraft ACLT Accelerate ACLTD Accelerated ACLTG Accelerating ACLTS Accelerates ACPY Accompany ACRS Across ACSL Altocumulus standing lenticular ACTV Active ACTVTY Activity ACYC Anticyclone ADJ Adjacent ADL Additional ADQT Adequate ADQTLY Adequately ADRNDCK Adirondack ADVCT Advect ADVCTD Advected ADVCTG Advecting ADVCTN Advection ADVCTS Advects ADVN Advance ADVNG Advancing ADVY Advisory ADVYS Advisories AF CT Affect AF CTD Affected AF CTG Affecting AF DK After dark AF OS Automated Field Operations System AF SS Automated Flight Service Station AFT After AF TN Afternoon AGL Above ground level AGN Again 146 AGRD Agreed AGRS Agrees AGRMT Agreement AHD Ahead AK Alaska AL Alabama ALF Aloft ALG Along ALGHNY Allegheny ALQDS All quadrants ALSTG Altimeter setting ALT Altitude ALTA Alberta ALTHO Although ALTM Altimeter ALUTN Aleutian AMD Amend AMDD Amended AMDG Amending AMDT Amendment AMP Amplify AMPG Amplifying AMPLTD Amplitude AMS Air mass AMT Amount ANLYS Analysis ANS Answer AOA At or above AOB At or below AP Anomalous Propagation APCH Approach APCHG Approaching APCHS Approaches APLCN Appalachian APLCNS Appalachians APPR Appear APPRG Appearing APPRS Appears APRNT Apparent APRNTLY Apparently APRX Approximate APRXLY Approximately AR Arkansas ARL 7 Air Resources Lab ASAP As soon as possible ASSOCD Associated ASSOCN Association ATLC Atlantic ATTM At this time ATTN Attention AVBL Available AVG Average AVN Aviation model AWC 7 Aviation Weather Center AWT Awaiting AZ Arizona AZM Azimuth BACLIN Baroclinic BAJ A Baja California BATROP Barotropic BC British Columbia BCH Beach BCKG Backing BCM Become BCMG Becoming BCMS Becomes BDA Bermuda BDRY Boundary BFDK Before dark BFR Before BGN Begin BGNG Beginning BGNS Begins BHND Behind BINOVC Breaks in overcast BKN Broken BLD Build BLDG Building BLDUP Buildup BLKHLS Black Hills BLKT Blanket BLKTG Blanketing BLKTS Blankets BLO Below clouds BLW Below BLZD Blizzard BN Blowing sand BND Bound BNDRY Boundary BNDRYS Boundaries BNTH Beneath BOOTHEEL Bootheel 147 December 1999 BR Branch BRKG Breaking BRKPHC Breaks in higher clouds BRKS Breaks BRKSHR Berkshire BRM Barometer BS Blowing snow BTWN Between BYD Beyond C Celsius CA California CAA Cold air advection CARIB Caribbean CASCDS Cascades CB Cumulonimbus CC Cirrocumulus CCLDS Clear of clouds CCLKWS Counterclockwise CCSL Cirrocumulus standing lenticular CDFNT Cold front CFP Cold front passage CHC Chance CHCS Chances CHG Change CHGD Changed CHGG Changing CHGS Changes CHSPK Chesapeake CI Cirrus CIG Ceiling CIGS Ceilings CLD Cloud CLDNS Cloudiness CLDS Clouds CLKWS Clockwise CLR Clear CLRG Clearing CLRS Clears CMPLX Complex CNCL Cancel CNCLD Canceled CNCLG Canceling CNCLS Cancels CNDN Canadian CNTR Center CNTRD Centered December 1999 CNTRL Central CNTY County CNTYS Counties CNVG Converge CNVGG Converging CNVGNC Convergence CNVTN Convection CNVTV Convective CNVTVLY Convectively CONFDC Con dence CO Colorado COMPR Compare COMPRG Comparing COMPRD Compared COMPRS Compares COND Condition CONT Continue CONTD Continued CONTLY Continually CONTG Continuing CONTRAILS Condensation trails CONTS Continues CONTDVD Continental Divide CONUS Continental US COORD Coordinate COR Correction CPBL Capable CRC Circle CRLC Circulate CRLN Circulation CRNR Comer CRNRS Comers CRS Course CS Cirrostratus CSDR Consider CSDRBL Considerable CST Coast CSTL Coastal CT Connecticut CTGY Category CTSKLS Catskills CU Cumulus CUFRA Cumulus fractus CVR Cover CVRD Covered CVRG Covering CVRS Covers CWSU Center Weather Service Units CYC Cyclonic CYCLGN Cyclogenesis DABRK Daybreak DALGT Daylight DBL Double DC District of Columbia DCR Decrease DCRD Decreased DCRG Decreasing DCRGLY Decreasingly DCRS Decreases DE Delaware DEG Degree DEGS Degrees DELMARVA DelawareMarylandVirginia DFCLT Dif cult DFCLTY Dif culty DFNT De nite DFNTLY De nitely DFRS Differs DFUS Diffuse DGNL Diagonal DGNLLY Diagonally DIGG Digging DIR Direction DISC Discontinue DISCD Discontinued DISCG Discontinuing DISRE Disregard DISRED Disregarded DISREG Disregarding DKTS Dakotas DLA Delay DLAD Delayed DLT Delete DLTD Deleted DLTG Deleting DLY Daily DMG Damage DMGD Damaged DMGG Damaging DMNT Dominant DMSH Diminish DMSHD Diminished DMSHG Diminishing DMSHS Diminishes DNS Dense DNSLP Downslope DNSTRM Downstream DNWND Downwind DP Deep DPND Deepened DPNG Deepening DPNS Deepens DPR Deeper DPTH Depth DRFT Drift DRFTD Drifted DRFTG Drifting DRFTS Drifts DRZL Drizzle DSCNT Descent DSIPT Dissipate DSIPTD Dissipated DSIPTG Dissipating DSIPTN Dissipation DSIPTS Dissipates DSND Descend DSNDG Descending DSNDS Descends DSNT Distant DSTBLZ Destabilize DSTBLZD Destabilized DSTBLZG DestabiliZing DSTBLZS Destabilizes DSTBLZN Destabilization DSTC Distance DTRT Deteriorate DTRTD Deteriorated DTRTG Deteriorating DTRTS Deteriorates DURC During climb DURD During descent DURG During DURN Duration DVLP Develop DVLPD Developed DVLPG Developing DVLPMT Development DVLPS Develops DVRG Diverge DVRGG Diverging DVRGNC Divergence DVRGS Diverges DVV Downward vertical velocity DWNDFTS Downdrafts DWPNT Dew point DWPNTS Dew points E E East December 1999 EBND Eastbound EFCT Effect ELNGT Elongate ELNGTD Elongated ELSW Elsewhere EMBDD Embedded EMERG Emergency ENCTR Encounter ENDG Ending ENE Eastnortheast ENELY Eastnortheasterly ENERN Eastnortheastem ENEWD Eastnortheastward ENHNC Enhance ENHNCD Enhanced ENHNCG Enhancing ENHNCS Enhances ENHNCMNT Enhancement ENTR Entire ERN Eastern ERY Early ERYR Earlier ESE Eastsoutheast ESELY Eastsoutheasterly ESERN Eastsoutheastem ESEWD Eastsoutheastward ESNTL Essential ESTAB Establish EST Estimate ETA Estimated time of arrival or ETA model ETC Et cetera ETHVI Elapsed time EVE Evening EWD Eastward EXCLV Exclusive EXCLVLY Exclusively EXTDG Extending EXTDS Extends EXTN Extension EXTRAP Extrapolate EXTRAPD Extrapolated EXTRM Extreme EXTRMLY Extremely EXTSV Extensive December 1999 F Fahrenheit FA Aviation area forecast FAM Familiar FCST Forecast FCSTD Forecasted FCSTG Forecasting FCSTR Forecaster FCSTS Forecasts FIG Figure FILG Filling FIR 7 Flight information region FIRAV First available FL Florida or ight level FLG Falling FLRY Flurry FLRYS Flurries FLT Flight FLW Follow FLWG Following FM From FMT Format FNCTN Function FNTS Fronts FNTGNS Frontogenesis FNTLYS Frontolysis FORNN Forenoon FPM Feet per minute FQT Frequent FQTLY Frequently FRM Form FRMG Forming FRMN Formation FROPA Frontal passage FROSFC Frontal surface FRST Frost FRWF Forecast wind factor FRZ Freeze FRZLVL Freezing level FRZN Frozen FRZG Freezing FT Feet FTHR Further FVRBL Favorable FWD Forward FYI For your information G 1410 G Gust GA Georgia GEN General GENLY Generally GEO Geographic GEOREF Geographical reference GF Fog GICG Glaze icing GLFALSK Gulf of Alaska GLFCAL Gulf of California GLFMEX Gulf of Mexico GLFSTLAWR Gulf of St Lawrence GND Ground GRAD Gradient GRDL Gradual GRDLY Gradually GRT Great GRTLY Greatly GRTLKS Great Lakes GSTS Gusts GSTY Gusty GTS 7 Global Telecommunication System H HAZ Hazard HDFRZ Hard freeze HDSVLY Hudson Valley HDWND Head wind HGT Height IH High IH Hawaii HIFOR High level forecast HLF Half HLTP Hilltop HLSTO Hailstones HND Hundred HPC 7 Hydrometeorological Prediction Center HR Hour HRS Hours HRZN Horizon HTG Heating HURCN Hurricane HUREP Hurricane report HV Have HVY Heavy HVYR Heavier HVYST Heaviest HWVR However HWY Highway IA Iowa IC Ice in PIREPs only ICAO International Civil Aviation Organization ICG Icing ICGIC Icing in clouds ICGICIP Icing in clouds and in precipitation ICGIP Icing in precipitation ID Idaho IFR Instrument ight rules IL Illinois IMDT Immediate IMDTLY Immediately IMPL Impulse IMPLS Impulses IMPT Important INCL Include INCLD Included INCLG Including INCLS Includes INCR Increase INCRD Increased INCRG Increasing INCRGLY Increasingly INCRS Increases INDC Indicate INDCD Indicated INDCG Indicating INDCS Indicates INDEF Indefinite INFO Information INLD Inland INSTBY Instability INTCNTL Intercontinental INTL International INTMD Intermediate INTMT Intermittent INTMTLY Intermittently INTR Interior INTRMTRGN Interrnountain region INTS Intense INTSFCN Intensification INTSFY Intensify INTSFYD Intensi ed INTSFYG Intensifying INTSFYS Intensi es INTSTY Intensity 1411 December 1999 INTVL Interval INVRN Inversion IOVC In overcast INVOF In vicinity of IP Ice pellets IPV Improve IPVG Improving ISOL Isolate ISOLD Isolated JCTN Junction JTSTR Jet stream K KFRST Killing frost KLYR Smoke layer aloft KOCTY Smoke over city KS Kansas KT Knots KY Kentucky LA Louisiana LABRDR Labrador LAT Latitude LAWRS Limited aviation weather reporting station LCL Local LCLY Locally LCTD Located LCTN Location LCTMP Little change in temperature LEVEL Level LFTG Lifting LGRNG Longrange LGT Light LGTR Lighter LGWV Long wave LI Lifted Index LIS Lifted Indices LK Lake LKS Lakes LKLY Likely LLJ Low level jet LLWAS Lowlevel wind shear alert system LLWS Lowlevel wind shear LMTD Limited December 1999 LMTG Limiting LMTS Limits LN Line LO Low LONG Longitude LONGL Longitudinal LRG Large LRGLY Largely LRGR Larger LRGST Largest LST Local standard time LTD Limited LTG Lightning LTGCC Lightning cloudtocloud LTGCG Lightning cloudtoground LTGCCCG Lightning cloudtocloud cloudto ground LTGCW Lightning cloudtowater LTGIC Lightning in cloud LTL Little LTLCG Little change LTR Later LTST Latest LV Leaving LVL Level LVLS Levels LWR Lower LWRD Lowered LWRG Lowering LYR Layer LYRD Layered LYRS Layers MA Massachusetts MAN Manitoba MAX Maximum MB Millibars MCD Mesoscale discussion MD Maryland MDFY Modify MDFYD Modi ed MDFYG Modifying MDL Model MDLS Models MDT Moderate MDTLY Moderately ME Maine MED Medium MEGG Merging MESO Mesoscale MET Meteorological METAR Aviation routine weather report METRO Metropolitan MEX Mexico MHKVLY Mohawk Valley MI Michigan MID Middle MIDN Midnight MIL Military MIN Minimum MISG Missing MLTLVL Melting level MN Minnesota MNLD Mainland MNLY Mainly MO Missouri MOGR Moderate or greater MOV Move MOVD Moved MOVG Moving MOVMT Movement MOVS Moves MPH Miles per hour MRGL Marginal MRGLLY Marginally MRNG Morning MRTM Maritime MS Mississippi MSG Message MSL Mean sea level MST Most MSTLY Mostly MSTR Moisture MT Montana MTN Mountain MTNS Mountains MULT Multiple MULTILVL Multilevel MWO 7 Meteorological Watch Office MXD Mixed N North NAB Not above NAT North Atlantic NATL National NAV Navigation NB New Brunswick 1412 NBND Northbound NBRHD Neighborhood NC North Carolina NCEP National Center of Environmental Prediction NCO 7 NCEP Central Operations NCWX No change in weather ND North Dakota NE Northeast NEB Nebraska NEC Necessary NEG Negative NEGLY Negatively NELY Northeasterly NERN Northeastern NEWD Northeastward NEW ENG New England NFLD Newfoundland NGM Nested grid model NGT Night NH New Hampshire NIL None N New Jersey NL No layers NLT Not later than NLY Northerly NM New Mexico NMBR Number NMBRS Numbers NML Normal NMRS Numerous NNE Northnortheast NNELY Northnortheasterly NNERN Northnortheastern NNEWD Northnortheastward NNW Northnorthwest NNWLY Northnorthwesterly NNWRN Northnorthwestern NNWWD Northnorthwestward NNNN End ofmessage NOAA National Oceanic and Atmospheric Administration NOPAC Northern Paci c NPRS Nonpersistent NR Near NRLY Nearly NRN Northern NRW Narrow NS Nova Scotia NTFY Notify NTFYD Noti ed 1413 December 1999 NV Nevada NVA Negative vorticity advection NW Northwest NWD Northward NWLY Northwesterly NWRN Northwestern NWS National Weather Service NY New York NXT Next 0 OAT Outside air temperature OBND Outbound OBS Observation OBSC Obscure OBSCD Obscured OBSCG Obscuring OCFNT Occluded front OCLD Occlude OCLDS Occludes OCLDD Occluded OCLDG Occluding OCLN Occlusion OCNL Occasional OCNLY Occasionally OCR Occur OCRD Occurred OCRG Occurring OCRS Occurs OFC Of ce OFP Occluded frontal passage OFSHR Offshore OH Ohio OK Oklahoma OMTNS Over mountains ONSHR On shore OR Oregon ORGPHC Orographic ORIG Original OSV Ocean station vessel OTLK Outlook OTP On top OTR Other OTRW Otherwise OUTFLO Out ow OVC Overcast OVHD Overhead OVNGT Overnight OVR Over OVRN Overrun December 1999 OVRNG Overrunning OVTK Overtake OVTKG Overtaking OVTKS Overtakes PA Pennsylvania PAC Pacific PATWAS Pilot s automatic telephone weather answering service PBL Planetary boundary layer PCPN Precipitation PD Period PDMT Predominant PEN Peninsula PERM Permanent PGTSND Puget Sound PHYS Physical PIBAL Pilot balloon observation PIREP Pilot weather report PL 7 Ice pellets PLNS Plains PLS Please PLTO Plateau PM Postmeridian PNHDL Panhandle POS Positive POSLY Positively PPINA Radar weather report not available PPINE Radar weather report no echoes observed PPSN Present position PRBL Probable PRBLY Probably PRBLTY Probability PRECD Precede PRECDD Preceded PRECDG Preceding PRECDS Precedes PRES Pressure PRESFR Pressure falling rapidly PRESRR Pressure rising rapidly PRIM Primary PRIN Principal PRIND Present indications are PRJMP Pressure jump PROB Probability PROC Procedure PROD Produce PRODG Producing PROG Forecast PROGD Forecasted PROGS Forecasts PRSNT Present PRSNTLY Presently PRST Persist PRSTS Persists PRSTNC Persistence PRSTNT Persistent PRVD Provide PRVDD Provided PRVDG Providing PRVDS Provides PS Plus PSBL Possible PSBLY Possibly PSBLTY Possibility PSG Passage PSN Position PSND Positioned PTCHY Patchy PTLY Partly PTNL Potential PTNLY Potentially PTNS Portions PUGET Puget Sound PVA Positive vorticity advection PVL Prevail PVLD Prevailed PVLG Prevailing PVLS Prevails PVLT Prevalent PWB Pilot weather briefing PWR Power Q QN Question QSTNRY Quasistationary QTR Quarter QUAD Quadrant QUE Quebec R Rain RADAT Radiosonde additional data RAOB Radiosonde observation RCH Reach RCHD Reached RCHG Reaching RCHS Reaches RCKY Rocky RCKYS Rockies RCMD Recommend RCMDD Recommended RCMDG Recommending RCMDS Recommends RCRD Record RCRDS Records RCV Receive RCVD Received RCVG Receiving RCVS Receives RDC Reduce RDGG Ridging RDVLP Redevelop RDVLPG Redeveloping RDVLPMT Redevelopment RE Regard RECON Reconnaissance REF Reference RES Reserve REPL Replace REPLD Replaced REPLG Replacing REPLS Replaces REQ Request REQS Requests REQSTD Requested RESP Response RESTR Restrict RGD Ragged RGL Regional model RGLR Regular RGN Region RGNS Regions RGT Right RH Relative humidity RI Rhode Island RIOGD Rio Grande RLBL Reliable RLTV Relative RLTVLY Relatively RMK Remark RMN Remain RMND Remained RMNDR Remainder RMNG Remaining RMNS Remains 1415 December 1999 RNFL Rainfall ROTG Rotating ROTS Rotates RPD Rapid RPDLY Rapidly RPLC Replace RPLCD Replaced RPLCG Replacing RPLCS Replaces RPRT Report RPRTD Reported RPRTG Reporting RPRTS Reports RPT Repeat RPTG Repeating RPTS Repeats RQR Require RQRD Required RQRG Requiring RQRS Requires RSG Rising RSN Reason RSNG Reasoning RSNS Reasons RSTR Restrict RSTRD Restricted RSTRG Restricting RSTRS Restricts RTRN Return RTRND Returned RTRNG Returning RTRNS Returns RUF Rough RUFLY Roughly RVS Revise RVSD Revised RVSG Revising RVSS Revises RWY Runway S South SAB 7 Satellite Analysis Branch SASK Saskatchewan SATFY Satisfactory SBND Southbound SBSD Subside December 1999 SBSDD Subsided SBSDNC Subsidence SBSDS Subsides SC South Carolina or stratocumulus SCND Second SCNDRY Secondary SCSL Stratocumulus standing lenticular SCT Scatter SCTD Scattered SCTR Sector SD South Dakota SE Southeast SEC Second SELY Southeasterly SEPN Separation SEQ Sequence SERN Southeastern SEV Severe SEWD Southeastward SFC Surface SG Snow grains SGFNT Signi cant SGFNTLY Significantly SHFT Shift SHFTD Shifted SHFTG Shifting SHFTS Shifts SHLD Shield SHLW Shallow SHRT Short SHRTLY Shortly SHRTWV Shortwave SHUD Should SHWR Shower SIERNEV Sierra Nevada SIG Signature SIGMET Significant meteorological information SIMUL Simultaneous SKC Sky clear SKED Schedule SLD Solid SLGT Slight SLGTLY Slightly SLO Slow SLOLY Slowly SLOR Slower SLP Slope SLPG Sloping SLW Slow SLY Southerly 1416 SM Statute mile SML Small SMLR Smaller SMRY Summary SMTH Smooth SMTHR Smoother SMTHST Smoothest SMTM Sometime SMWHT Somewhat SN Snow SNBNK Snowbank SNFLK Snow ake SNGL Single SNOINCR Snow increase SNOINCRG Snow increasing SNST Sunset SOP Standard operating procedure SPC 7 Storm Prediction Center SPCLY Especially SPD Speed SPKL Sprinkle SPLNS Southern Plains SPRD Spread SPRDG Spreading SPRDS Spreads SPRL Spiral SQ Squall SQLN Squall line SR Sunrise SRN Southern SRND Surround SRNDD Surrounded SRNDG Surrounding SRNDS Surrounds SS Sunset SSE Southsoutheast SSELY Southsoutheasterly SSERN Southsoutheastem SSEWD Southsoutheastward SSW Southsouthwest SSWLY Southsouthwesterly SSWRN Southsouthwestern SSWWD Southsouthwestward ST Stratus STAGN Stagnation STBL Stable STBLTY Stability STD Standard STDY Steady STFR Stratus fractus STFRM Stratiform STG Strong STGLY Strongly STGR Stronger STGST Strongest STM Storm STMS Storms STN Station STNRY Stationary SUB Substitute SUBTRPCL Subtropical SUF Suf cient SUFLY Sufficiently SUG Suggest SUGG Suggesting SUGS Suggests SUP Supply SUPG Supplying SUPR Superior SUPSD Supersede SUPSDG Superseding SUPSDS Supersedes SVG Serving SVRL Several SW Southwest SWD Southward SWWD Southwestward SWLY Southwesterly SWRN Southwestern SX Stability index SXN Section SYNOP Synoptic SYNS Synopsis SYS System T TAF Aviation terminal forecast TCNTL Transcontinental TCU Towering cumulus TDA Today TEMP Temperature THK Thick THKNG Thickening THKNS Thickness THKR Thicker THKST Thickest THN Thin THNG Thinning THNR Thinner THNST Thinnest THR Threshold 1417 December 1999 THRFTR Thereafter THRU Through THRUT Throughout THSD Thousand THTN Threaten THTND Threatened THTNG Threatening THTNS Threatens TIL Until TMPRY Temporary TMPRYLY Temporarily TMW Tomorrow TN Tennessee TNDCY Tendency TNDCYS Tendencies TNGT Tonight TNTV Tentative TNTVLY Tentatively TOPS Tops TOVC Top of overcast TPG Topping TRBL Trouble TRIB Tributary TRKG Tracking TRML Terminal TRMT Terminate TRMTD Terminated TRMTG Terminating TRMTS Terminates TRNSP Transport TRNSPG Transporting TROF Trough TROFS Troughs TROP Tropopause TRPCD Tropical continental air mass TRPCL Tropical TRRN Terrain TRSN Transition TS Thunderstorm TSFR Transfer TSFRD Transferred TSFRG Transferring TSFRS Transfers TSNT Transient TURBC Turbulence TURBT Turbulent TWD Toward TWDS Towards TWI Twilight TWRG Towering TX Texas December 1999 U UA Pilot weather reports UDDF Up and downdrafts UN Unable UNAVBL Unavailable UNEC Unnecessary UNKN Unknown UNL Unlimited UNRELBL Unreliable UNRSTD Unrestricted UNSATFY Unsatisfactory UNSBL Unseasonable UNSTBL Unstable UNSTDY Unsteady UNSTL Unsettle UNSTLD Unsettled UNUSBL Unusable UPDFTS Updrafts UPR Upper UPSLP Upslope UPSTRM Upstream URG Urgent USBL Usable UT Utah UTC 7 Universal Time Coordinate UVV Upward vertical velocity UWNDS Upper winds VA Virginia VAAC 7 Volcanic Ash Advisory Center VAAS 7 Volcanic Ash Advisory Statement VAL Valley VARN Variation VCNTY Vicinity VCOT VFR conditions on top VCTR Vector VFR Visual ight rules VFY Verify VFYD Verified VFYG Verifying VFYS Verifies VLCTY Velocity VLCTYS Velocities VLNT Violent VLNTLY Violently 1418 VMC Visual meteorological conditions VOL Volume VORT Vorticity VR Veer VRG Veering VRBL Variable VRISL Vancouver Island BC VRS Veers VRT MOTN Vertical motion VRY Very VSB Visible VSBY Visibility VSBYDR Visibility decreasing rapidly VSBYIR Visibility increasing rapidly VT Vermont VV Vertical velocity W W West WA Washington WAA Warm air advection WAF S 7 Word Area Forecast System WBND Westbound WDLY Widely WDSPRD Widespread WEA Weather WFO Weather Forecast Office WFSO Weather Forecast Service Office WFP Warm front passage WI Wisconsin WIBIS Will be issued WINT Winter WK Weak WKDAY Weekday WKEND Weekend WKNG Weakening WKNS Weakens WKR Weaker WKST Weakest WKN Weaken WL Will WLY Westerly WND Wind WNDS Winds WNW Westnorthwest WNWLY Westnorthwesterly WNWRN Westnorthwestern WNWWD Westnorthwestward WO Without WPLTO Western Plateau WRM Warm WRMG Warming WRN Western WRMR Warmer WRMST Warmest WRMFNT Warm front WRMFNTL Warm frontal WRNG Warning WRS Worse WS Wind shear WSHFT Windshift WSFO Weather Service Forecast Office WSTCH Wasatch Range WSW Westsouthwest WSWLY Westsouthwesterly WSWRN Westsouthwestem WSWWD Westsouthwestward WTR Water WTSPT Waterspout WUD Would WV West Virginia WVS Waves WW Severe weather watch WWD Westward WX Weather WY Wyoming XCP Except 1419 December 1999 XPC Expect XPCD Expected XPCG Expecting XPCS Expects XPLOS Explosive XTND Extend XTNDD Extended XTNDG Extending XTRM Extreme XTRMLY Extremely Y YDA Yesterday YKN Yukon YLSTN Yellowstone ZN Zone ZNS Zones December 1999 SCHEDULED ISSUANCE AND VALID TIMES OF FORECAST PRODUCTS Table 141 shows scheduled issuance and valid times of the TAFs All times are UTC Table 14 1 Scheduled Issuance and Valid Times of TAFs Scheduled Issuance Valid Period Transmission The Table 142 has scheduled issuance and valid times of the TWEBs All times are UTC Table 14 2 Scheduled Issuance and Valid Times of TWEBs Scheduled Valid Period Transmission Table 143 shows the scheduled issuance times of the FAs for their respective areas The FA is valid 1 hour after issuance time All times are UTC The times the FA is issued depends on whether the FA area is in local standard or local daylight time Table 14 3 Scheduled Issuance Times of FAs Area Boston and Chicago and San Francisco and Alaska Hawaii Forecast Miami Ft Worth Salt Lake City LDTLST Table 144 shows the scheduled issuance times of the Gulf of Mexico FA All times are UTC Table 14 4 Scheduled Issuance Times ofthe Gulf of Mexico FA Gulf of Mexico FA Issuance Times LDTLST 1st issuance 10401140 2 d issuance 17401840 1420 December 1999 NATIONAL WEATHER SERVICE STATION IDENTIFIERS NORTHEAST REGION AKQ NorfolkWakefield VA ALY AlbanyEast Beme NY BGM Binghamton NY BOX BostonTaunton MA BTV Burlington VT BUF Buffalo NY CLE Cleveland OH CTP State College PA GYX PortlandGray ME ILN CincinnatiWilmington OH LWX Washington DC Sterling VA OKX New York CityBrookhaven NY PBZ PittsburghCoraopolis PA PHI Philadelphia PAMount Holly NJ RLX CharlestonRuthdale WV RNK RoanokeBlacksburg VA SOUTHCENTRAL REGION AMA Amarillo TX BMX Birmingham AL BRO Brownsville TX CRP Corpus Christi TX EPZ El Paso TXSanta Theresa NM EWX Austin San Antonio TX FWD DallasForth Worth TX HGX HoustonDickinson TX JAN Jackson MS LCH Lake Charles LA LIX New OrleansSlidell LA LUB Lubbock TX LZK North Little Rock AR MAF Midland TX MEG MemphisGermantown TN MOB Mobile MS MRX KnoxvilleTri Cities TN OHX Nashville Old Hickory TN OUN Oklahoma CityNorman OK SHV Shreveport LA SJT San Angelo TX TSA Tulsa OK 1421 SOUTHEAST REGION CAE Columbia SC CHS Charleston SC FFC AtlantaPeachtree City GA GSP GreenvilleSpartanburgGreer SC ILM Wilmington NC JAX Jacksonville FL MFL Miami FL MHX Morehead CityNewport NC MLB Melbourne FL RAH RaleighDurham NC TAE Tallahassee FL TBW TampaRuskin FL TJSJ San Juan PR MOUNTAIN REGION ABQ Albuquerque NM BIL Billings MT BOI Boise ID BOU DenverBoulder CO CYS Cheyenne WY FGZ FlagstaffBellemont AZ GGW Glasgow MT GJT Grand Junction CO LKN Elko NV MSO Missoula MT PIH Pocatello ID PSR Phoenix AZ PUB Pueblo CO REV Reno NV RIW Riverton WY SLC Salt Lake City UT TFX Great Falls MT TWC Tucson AZ VEF Las Vegas NV N ORTHCEN TRAL REGION ABR Aberdeen SD APX Alpena Gaylord MI ARX La Crosse WI BIS Bismarck ND DDC Dodge City KS DLH Duluth MN DMX Des MoinesJohnston IA DTX DetroitPontiac MI DVN Quad CitiesDavenport IA December 1999 FGF FargoGrand Forks ND PHFO Honolulu IH EAX Kansas CityPleasant Hill MO FSD Sioux Falls SD GID Hastings NE GLD Goodland KS GRB Green Bay WI GRR Grand Rpaids MI ICT Wichita KS ILX Lincoln IL IND Indianapolis IN JKL JacksonNoctor KY LBF North Platte NE LMK Louisville KY LOT ChicagoRomeoville IL LSX St Louis MO MPX MinneapolisChanhassen MN MKX MilwaukeeDousman WI MQT Marquette MI OAX OmahaValley NE PAH Paducah KY SGF Spring eld MO TOP Topeka KS UNR Rapid City SD WEST COAST REGION EKA Eureka CA HNX Hanford CA LOX Los AngelesOxnard CA MFR Medford OR MTR San FranciscoMonterey CA OTX Spokane WA PDT Pendelton OR PQR Portland OR SEW Seattle WA SGX San Diego CA STO Sacramento CA ALASKAN REGION PAF C Anchorage AK PAFG Fairbanks AK PAJK Juneau AK PACIFIC REGION PGUA Tiyan GU 1422