MET1010 Chapter 9 11 Review Chapter 9 Time Ranges of Weather Forecasts Use computer models mostly Seasonal forecasts Outlooks Climate change Exceeds 8 5 Day Long Range Forecasts 3 8 5 Days Medium Range Forecasts 6 hours to a few days Short Range Forecasts Use radar data mostly Nowcasts Minutes to a few hours Procedure for Computer Forecasts Gather current data Input to computer models that simulate atmosphere Forecaster analyzes output and adds skill Standard land based like TLH airport Issue forecast Surface Data Ocean buoys Ships Aircraft reports Geostationary Satellites See clouds Cloud Track Winds The geostationary satellite moves through space at the same rate that the earth rotates so it remains above a fixed spot on the equator and monitors one area constantly Infrared Images Sees temp of cloud top whiter colder higher grey warmer lower On an enhanced infrared image red colder higher Typical cloud images infer weather systems Sees humid and dry areas in mid troposphere Water Vapor Images Brown dry Green humid Polar Orbiting Satellites Assimilate all the Data Get 3 D depiction Current situation Chaos every time a butterfly flaps its wings The Most Basic Equations for Computer Models Equations actually used much more complex Parameterization 3 D Forecasts created in short time steps Two Outputs Valid at Same Time Which to believe NAM WRS or GFS About 300 mi above surface Get temperature and RH soundings but poor vertical resolution Polar orbiting satellites scan from north to south and on each successive orbit the satellite scans an area farther to the west Ensemble forecasting of same model 48 hours into the future The chart is constructed by running the model 15 different times each time beginning with a slightly different initial condition The blue lines represent the 5790 meter contour line the red lines the 5940 meter contour line and the green line the 500 mb 25 year average called climatology Vocabulary Watch indicates that atmospheric conditions favor hazardous weather occurring over a particular region during a specified time period Warning indicates that hazardous weather is either imminent or actually occurring within AWIPS helps handle all the available charts and maps and is a high speed data modeling a specified forecast area system that using computers station over a given period of time Meteogram a chart that shows how one or more weather variables has changed at a Sounding a two dimensional vertical profile of temperature dew point and winds Analysis the final chart that interprets weather patterns Numerical weather prediction the routine daily forecasting of weather by the computer using mathematical equations Atmospheric models describes the present state of the atmosphere Prognostic chart prog the final forecast chart representing the atmosphere at a specified future time Chaos small unpredictable atmospheric fluctuations Ensemble forecasting technique that involves running several forecast models each beginning with slightly different weather information to reflect the errors inherent in the measurements Persistence forecast a prediction that future weather will be the same as present weather Steady state trend forecast principle that surface weather systems tend to move in the same direction and at approximately the same speed as they have been moving Analogue method relies on the fact that existing features on a weather chart may strongly resemble features that produced certain weather conditions sometime in the past Statistical forecasts made routinely of weather elements based on the past performance of computer models Probability forecast forecast based on an average in the past to show likelihood Weather types weather patterns put into groups using such criteria as the position of the subtropical highs the upper level flow and the prevailing storm track Climatological forecast a forecast based on the climate of a particular region Nowcast a weather forecast for up to a few hours usually no more than 6 Short range forecasts weather forecast that range from about 6 hours to a few days Medium range forecast forecast that extends from about 3 to 8 days into the future Long range forecast forecast that extends beyond about 8 days Outlooks summary of general trends that cover 6 to 10 day and 8 to 14 day periods Chapter 10 Thunderstorms Convective storms that form with rising air Begins with a rising parcel of unstable air Triggered by things such as turbulent eddies unequal surface heating terrain Three requirements for a thunderstorm Adequate moisture especially near the surface Conditional instability Source of vertical motion a low a front a thermal flow over a mountain etc For a severe storm a fourth requirement is needed strong vertical wind shear winds change rapidly with height Produce one of the following large hail strong surface gust winds or a tornado More severe thunderstorms in east south especially southeast such as Florida Thunderstorms can also occur in cold weather when cold air aloft destabilizes the atmosphere and parcels of air move up because they remain warmer less dense than the colder air around them Ordinary Cell Thunderstorms Ordinary cell thunderstorm a thunderstorm produced by local convection within a conditionally unstable air mass Tend to form in warm humid air masses away from weather fronts Non severe thunderstorms or simple thunderstorms because they rarely become Often form along shallow zones where surface winds converge there is limited vertical severe wind shear Total life about 1 hour Three stages Cumulus growth stage Rising warm humid air develops into a cumulus cloud Updrafts only No precipitation reaches the ground The updrafts keep droplets and ice crystals suspended up in the cloud Cloud starts to build above freezing level and cloud particles collide and grow Bergeron process and the particles start to fall because they are so heavy This causes entrainment in which drier air from around the cloud is drawn in This leads to evaporation hence the chilling of air This cold air begins to descend as a downdraft Mature stage The appearance of downdrafts marks the mature stage There are both updrafts and downdrafts the updrafts and downdrafts the cell This stage is the most intense the storm gets a thunderstorm is occurring Cloud extends to near the tropopause 30 000 ft More severe storms can be taller The cold downdrafts reach the surface and spread horizontally this is called the gust front This gust front forces
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