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CU / Marine Science / IMCS 1050 / What is a weather forecast?

What is a weather forecast?

What is a weather forecast?


School: University of Colorado
Department: Marine Science
Course: Weather & the Atmosphere
Professor: Melissa nigro
Term: Fall 2015
Cost: 50
Name: ATOC exam #3
Description: This review guide has all of the info you’ll need to be ready for the test! There is a lot of memorization to do for this test. There are definitions from the book, online sources, as well as videos, which will help you understand concepts. If there is anything I would recommend looking over separately from this study guide, it would be the chapter 8 topics. Good luck on the last midterm and have a
Uploaded: 11/17/2015
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ATOC 1050 Midterm #3 with Melissa Nigro

Chapters 8, 9, 10, 11

This review guide has all of the info you’ll need to be ready for the test! There is a lot  of memorization to do for this test and all of the definitions are here. There are  definitions from the book, online sources, as well as videos, which will help you  

understand concepts. Good luck on the last midterm and have a great Thanksgiving  break. ☺

What is a weather forecast?

Chapter 8:

Mid-Latitude Cyclones:

• Polar-front theory – a working model of how a mid-latitude cyclone progresses through the stages of birth, growth, and decay.

• Stages of cyclone life –

o Stationary front: a trough of lower pressure with higher pressure on  both sides. Cold air to the north and warm air to the south flow  We also discuss several other topics like Which of the three main processes of urine formation involves movement of waste from the peritubular capillary network to the distal convoluted tubule of a nephron so that it’s added to urine?

parallel to the front, but in opposite directions. This type of flow sets  up a cyclonic wind shear

o Frontal wave: a cold front pushing southward and a warm front  moving northward. The region of lowest pressure is at the junction of  the two fronts. As the cold air displaces the war air upward along the  cold front, and as war air rises ahead of the warm front, a narrow  band of precipitation forms.

It is a type of forecasting method that involves examining today's forecast scenario and remembering a day in the past when the weather scenario looked very similar. what is it?

We also discuss several other topics like What is fdic (1934)?

o Open wave: The central pressure of the wave cyclone is now much  lower, and several isobars encircle the wave’s apex. These more

tightly packed isobars create a stronger cyclonic flow, as the winds  swirl counterclockwise an downward toward the low’s center.  

Precipitation forms in a wide band ahead of the warm front and along  a narrow band on the cold front.

o Mature (initial occlusion): the cold front eventually overtakes the  warm front and the system becomes occluded. (This is when the  

storm is the most intense!)  

o Advanced occlusion: This happens as the occluded front becomes fully  developed. Without an ample supply of energy of rising, warm, moist  air, the system will dissipate.

What determines the movement of a weathersystem?

o Cut-off cyclone: This is the end stage where a precipitation-free area is  observed. In addition, only a weak cyclonic circulation is seen in the  wind field. We also discuss several other topics like Who wrote “an essay on the principle of population” (1798)?

Don't forget about the age old question of Professional dental supply has been successfully selling dental instruments to dentists for the past 20 years, and has developed strong customer relations. when looking for new marketing opportunities, professional dental supply will most likely look firs

Chapter 9

o What is a weather forecast – 1. Weather forecasting is the application of  science and technology to predict the state of the atmosphere for a given  location. 2. Weather forecasts are issued to save lives, to save property and  crops, and to tell us what to expect in our atmospheric environment.  

o Weather organizations – World Meteorological Organization (WMO) is a  UN agency that makes sure that observation procedures do not vary among  nations. Weather observations from all around the world are sent to The  United States National Weather Service (NWS) branch: National Center for  Environmental Prediction (NCEP) – this is where they analyze the data. If you want to learn more check out What is magneto-optic disk?

o Watch  - indicates that atmospheric conditions favor hazardous weather  occurring over a particular region during a specified time period, but that the  actual location and time of the occurrence is uncertain.

o Warning – indicates that hazardous weather is either imminent or actually  occurring within the specified forecast area.

o Advisory – issued to inform the public of less hazardous conditions caused  by wind, dust, fog, snow, sleet, or freezing rain.  

o How do we observe weather - http://www.rmets.org/weather-and climate/observing Don't forget about the age old question of The dots around the symbol of lewis electron-dot symbol, represents what?

o Meteograms – a chart that shows how one or more weather variables has  changed at a station over a given period of time.

o Soundings – a two-dimensional vertical profile of temperature, dew point,  and winds.  

o Numerical weather prediction, MOS, ensemble forecasting o Numerical weather prediction uses mathematical models of the  atmosphere and oceans to predict the weather based on current  weather conditions.  

o Model Output Statistics (MOS) is a technique used to objectively  interpret numerical model output and produce site-specific guidance. o Ensemble forecasting is a numerical weather prediction method that  is used to attempt to generate a representative sample of the possible  future states of a dynamical system.

o Types of forecasting methods (i.e. persistence, analog, etc.) o Persistence forecast: a prediction that future weather will be the same  as present weather.

o Steady-state or trend forecasting: because surface weather systems  tend to move in the same direction and at approximately the same  speed as they have been moving, one can forecast when and where  the weather will arrive.

o Analogue method: It involves examining today's forecast scenario and  remembering a day in the past when the weather scenario looked  very similar (an analog). The forecaster would predict that the  weather in this forecast will behave the same as it did in the past.

o For example, suppose today is very warm, but a cold front is  approaching your area. You remember similar weather conditions one  last week, also a warm day with cold front approaching. You also  remember how heavy thunderstorms developed in the afternoon as  the cold front pushed through the area. Therefore, using the analog  method, you would predict that this cold front will also produce  thunderstorms in the afternoon.

o Statistical method: forecasts made routinely of weather elements  based on the past performance of computer models.

o Probability forecast: A probability forecast specifies how likely a  defined event is to occur, as a percentage, and can help users to assess  the risks associated with particular weather events to which they are  sensitive.  

o Types of forecasts (i.e. nowcast, short-range, etc.)

o Nowcast: a forecast for up to a few hours (usually not more than 6) o Short-range forecast: forecasts that range from about 6 hours to a few  days (generally up to 3 days or 72 hours).

o Medium-range forecast: extends from about 3 to 8 days.

o Long-range forecast: extends beyond 8 days.

o What determines the movement of a weather system?  o For short time intervals, mid-latitude cyclonic storms and fronts tend  to move in the same direction and at approximately the same speed as  they did during the previous six hours

o Low-pressure areas tend to move in a direction that parallels the  isobars in the warm air ahead of the cold front

o Lows tend to move toward the region of greatest surface pressure  drop, whereas highs tend to move toward the region of greatest  surface pressure rise.  

o Surface pressure systems tend to move in the same direction as the  wind at 5500m – the 500 mb level. The speed at which surface  systems move is about half the speed of the winds at this level.

Chapter 10

o Ordinary (air-mass) Thunderstorms – they go through multiple stages: o 1. Cumulus stage (or growth stage) they tend to form in warm, humid  air masses away from significant weather fronts. A parcel of warm,  humid air rises, it cools and condenses into a single cumulus cloud or  a cluster of clouds. The clouds will continue to grow as long as it is  constantly fed by rising air from below. There is no precipitation,  

thunder, or lightning yet.

o 2. Mature Stage - Storm is most intense, cloud tops can reach the  Tropopause - with overshooting tops, seen in satellite imagery. Ice  and water are both present in the cloud and perhaps lightning and  thunder. The storm is characterized by warm updraft and cold,  

downdraft, with precipitation reaching the surface. The downdraft  can produce strong, gusty winds at surface. 

o 3. Dissipating stage - Storm is dominated by the downdrafts.  

Precipitation intensity at the ground weakens and you end up with a  cold pool of air at the ground and warm air aloft. Hence, the storm has  stabilized the environment.  

o Severe thunderstorms - The National Weather Service defines a severe  thunderstorm as having large hail, at least 3/4 inches (0.75 inches) in  diameter, and/or damaging winds, at least 58 mph, or 50 knots.

o Supercell thunderstorms – In a region where there is strong vertical wind  shear (speed and/or directional shear), the thunderstorm may form in such a  way that the outflow of cold air from the downdraft never undercuts the  updraft. In such a storm, the windshear may be so strong as to create  horizontal spin, which, when tilted into the updraft, causes it to rotate. Here  is a more simple definition: An intense long-lasting thunderstorm with a  single violently rotating updraft.

o Squall lines – multicell thunderstorms may form as a line of thunderstorms.  The line of storms may form directly along a cold front and extend for  hundreds of kilometers. Sometimes squall lines develop in the warm air mass  tens to hundreds of kilometers ahead of a cold front.

o Roll clouds - A Roll cloud is a relatively rare, low-level horizontal, tube shaped accessory cloud completely detached from the cumulonimbus base,  unlike the more common shelf cloud. When present, it is located along the  gust front and most frequently observed on the leading edge of a line of  thunderstorms, a cold front or line squalls. The roll cloud will appear to be  slowly "rolling" about its horizontal axis.  

o Downbursts - a strong downdraft that causes an outflow of damaging winds  at or near the surface. These downdrafts are referred to as macrobursts or  microbursts, depending on their size. Downbursts are a serious hazard to  aircraft, especially during takeoffs and landings, because they produce large  and abrupt changes in the wind speed and direction near the ground.

o Flash floods – floods that develop with little to no advance warning. Floods  can cause a massive amount of damage and kill people.  

o Q: What causes rising motion? A: Convergence at the surface!

o Lightning – a discharge of electricity, a giant spark, which usually occurs in  mature thunderstorms.  (Check out this website for a clear explanation:  http://www.britannica.com/science/lightning-meteorology)

o Lightning occurs when regions of excess positive and negative charge  develop within the cloud. Typically, there is a large volume of positive  charge in the upper regions of the cloud, a large negative charge in the  center, and a small positive charge in the lower regions. These charges  reside on water drops, ice particles, or both.  

A preliminary breakdown process within the cloud initiates  

cloud-to-ground lightning, typically between the center region of  negative charge and the small positive charge below it. This process

creates a channel of partially ionized air—air in which neutral atoms  and molecules have been converted to electrically charged ones. Next,  a stepped leader (initial lightning stroke) forms and propagates  downward, following channels created by the preliminary breakdown  process. The leader is highly branched in the direction of its  propagation. Most leader channels are negatively charged. When the  stepped leader nears the ground, an upward, connecting discharge of  opposite polarity rises and meets it at a point typically about 30  meters (100 feet) above the ground. When the junction is complete,  the cloud is effectively connected to the ground, and a very bright  return stroke propagates back to the cloud at a speed about one-third  the speed of light, following the leader channel.

Lightning may travel within a cloud, from one cloud to another,  from a cloud to the surrounding air, or from a cloud to the ground.  The lightning stroke can heat the air through which it travels to an  incredible 54,000 degrees F (which is 5 times hotter than the surface  of the sun!). This extreme heat causes the air to expand explosively,  thus initiating a shock wave that becomes a booming sound wave  (thunder).

o Tornadoes

o What is a tornado – A tornado is a rapidly rotating column of air  extending down from a cumuliform cloud that blows around a small  area of intense low pressure with a circulation that reaches the  ground. (https://www.youtube.com/watch?v=BMLZpjRYK9Q)

o What are the different parts of a tornado? (I.e. wall cloud, funnel cloud, etc.) A funnel cloud is used to refer to a visible funnel that does  not tough the ground (If one just sees a funnel cloud, there might or  might not be a tornado…it might look as if there is no tornado because  it isn’t touching the ground, but don’t be so sure!).

o What is the life cycle of a tornado

▪ Dust-whirl stage: where dust swirling upward from the surface  marks the tornado’s circulation on the ground and a short  

funnel often extends downward from the thunderstorm’s base.  ▪ Mature stage: damage is most severe during this time as the  funnel reaches its greatest width and is almost vertical.

▪ Decay stage: the tornado begins stretching into the shape of a  rope. The tornado becomes thinner and greatly distorted  

before it finally dissipates.

o Q: What are the ideal conditions for the formation of a tornado? ▪ The answers are on this website!  

http://www.wunderground.com/resources/severe/tornadoF AQ.asp

o Watches vs. warnings:  

o A Tornado watch is issued by the NOAA Storm Prediction  Center meteorologists who watch the weather 24/7 across the  entire U.S. for weather conditions that are favorable for  tornadoes. A watch can cover parts of a state or several states.  Watch and prepare for severe weather and stay tuned to NOAA  Weather Radio to know when warnings are issued.

o A Tornado warning is issued by your local NOAA National  Weather Service Forecast Office meteorologists who watch the  weather 24/7 over a designated area. This means a tornado  has been reported by spotters or indicated by radar and there  is a serious threat to life and property to those in the path of  the tornado. ACT now to find safe shelter!

o How are tornadoes classified?

o Q: How do tornadoes form?

▪ A: They are usually the extreme result of a supercell  thunderstorm. During the storm cold air and warm air  

combine in a set pattern: the cold air drops as the warm air  rises. The warm air eventually twists into a spiral and forms the funnel cloud that we all associate with a tornado.

o How are tornadoes forecasted? What instrument is used? ▪ Doppler radars

o Distribution of tornado occurrences

Chapter 11

o Hurricanes: an intense storm of tropical origin, with sustained winds of at  least 64 knots (74mi/hr.), and with considerably higher gusts, which forms  over the warm northern Atlantic and eastern north pacific oceans.  

o Anatomy of a hurricane:  

o Eye: the relatively clear area at the center. Within the eye, winds are  light and clouds are mainly broken. The surface air pressure is VERY  low, around 955mb.

o Eyewall: adjacent to the eye is the eyewall, a ring of intense  thunderstorms that whirl around the storm’s center and may extend  upward to almost 18 km above sea level. (Heaviest precipitation is in  the eyewall)

o Q: Where do you have rising motion? Sinking motion? And what kind of  weather would you expect with each?

o A:  

o Q: What is needed for a hurricane to form? What will cause a hurricane to  strengthen? Dissipate?

o A: Hurricanes form over tropical waters where the winds are light, the  humidity is high in a deep layer extending up through the  

troposphere, and the surface water temperature is warm, typically  26.5 degrees C (80 degrees F) or greater, over a vast area. These  conditions usually prevail over the tropical and subtropical North  Atlantic and North Pacific oceans during the summer and early fall.

o http://spaceplace.nasa.gov/hurricanes/en/ 

o As long as a hurricane has a heat source, aka the water stays at 80  degrees F, it will survive.

o Hurricanes weaken rapidly when they travel over colder water and  lose their heat source.

o Q: Why don’t hurricanes form over the equator?

o A: Hurricanes do not form over the equator because the Coriolis effect  is 0.

o Q: How do hurricanes form?

o A: http://spaceplace.nasa.gov/hurricanes/en/ 

o A: http://earthobservatory.nasa.gov/Features/Hurricanes/ 

o What are the different stages for a hurricane?

o Tropical depression: the winds increase to between 20 and 34 knots  and several closed isobars appear about its center on a surface  weather map.

o Tropical storm: when the isobars are packed together and the winds  are between 35 and 64 knots (at this point, the storm gets a name) o Hurricane (tropical cyclone): when wind speeds reach 64 knots.

o Q: What wind speeds are needed to classify a storm as a hurricane? o A: at least 64 knots or 74mi/hr.

o Q: How are hurricanes classified?

o A: The Saffir-Simpson Hurricane Wind Scale

▪ http://www.nhc.noaa.gov/aboutsshws.php 

o Q: How are hurricanes named?

o A: http://oceanservice.noaa.gov/facts/storm-names.html 

On the next page you will find the alphabetized names for hurricane  naming: no need to memorize!!! Just something to know about.

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