Upper Air/RawinsondeReleased every 12 hours, when it is 12 at night and 12 at noon over the Greenwich time zoneMeasures temperature and humidityAs it goes upward it determines pressureTracked as it goes up so we know wind speed and directionThe World Meteorological OrganizationResponsible for the international exchange of weather data and certifies that the observation process does not vary between nations since all weather observations must be comparableMelbourne, Moscow, and Washington DC Where it all goes to be redistributedWhere Do Most People Get Their Forecasts?Radio…television…internet…newspapersAMS/NWARadio/TV seal of approval programsAMS certified broadcast meteorologistRadio stations are all recorded and you cant depend on it because its don’t by people who don’t know much about weather anywaysWeather Watches/Warnings/AdvisoriesNational weather serviceSole sourceWhen things come up on the bottom of the TV screenIssues watches, advisories, warningsWeather watchAtmospheric conditions are favorable for the type of weather specifiedGenerally larger geographic areaGenerally longer time span (4-6 hours)You can find yourself in a tornado watch when there is not a cloud in the sky, you just keep listening until you hear more laterYou shouldn’t really do anything but keep watchingWeather warningsThe type of weather specified is imminent or is occurringSmaller geographic areaGenerally shorter time spans (1/2-1 hour)Weather AdvisoryWhatever type of weather is specified is either occurring or is imminent but it is generally NOT life threateningFog, snow, freezing rain, sleetWeather Forecast Tools: ComputersNumerical weather prediction (NWP)Models are mathematical in natureComputer atmospheric models (progs)Models are run generally one to four times a day (00z, 06z, 12z, 18z)Data in and data outGiven how they are built all models have certain biasesWe use computers to try to predict the weatherProblems with NWP ModelsIf bad data in then bad data outModels make bad assumptionsCannot adequately interpret many of the factors that influence surface weatherThere is a lot of space with water which create gaps in computer readings because the computers are only over landSmall disturbances/small errors tend to be amplified (chaos) especially with timeWeather Forecast Tools: Methods of ForecastingPersistence forecastingShort termJust looking at the skyWhat it is now is what it will be a few hours from nowMiddle of the summer is the best time to do thisSteady state/trend forecastingIf a weather system is approaching your area at so many miles an hour when will it move overhead? Move to the east?Use this in the winterKey spots to watch are Cheyenne, Wyoming to see when the winds get to TexasDownfall is that it will change speedsDo this a lot with hurricanesAnalogue method forecastingEnsemble forecastingBy product generally of numerical weather predictionClimatological forecastingYou can tell things a lot about a climatological seasonYou can predict and use it in certain placesLong term climate numbers is when you can use itProbability forecastingVery misunderstood facet of forecastingPoint forecastForecaster certainty x areal coverage expected50% x 20% = 1000 or a 10% POPDoes not talk about how much of the time it will be rainingDoes not tell you how much area will be covered by rainWhen you say tomorrow 30% chance that time range for 6 am to 6 pmWe look at the forecaster’s certainty that rain will develop or move into those countiesAccuracy In Weather ForecastingShort term forecasts (today, tonight)85-90% accuracyMedium term forecasts (2-3 days)Longer range forecasts (4-8 days)Depends on the time of yearHigher accuracy rates during the summerNational Weather Service has a climate prediction group that creates an 8-14 day outlook70% accuracyBecomes necessarily vagueThunderstorm Basics2000 thunderstorms in progress at any given moment worldwideMore common in warmer, equatorial climatesMoisture, lift, and instability are important, two things you NEED to haveHeavily tied to mT air massUpdraft/Downdraft StrengthCumulus stageUpdraft is dominantNo rainMature stageDowndraft developsRaining and thunderingMust severe weatherUpdrafts and downdrafts coexistDissipation stageWhen its all downdraftCan be really strong windsThunderstorm ClimatologyIn Austin we on average see 42-43 thunderstorms days a yearIn the last 20 years we have seen as many as 73 days and as little as 20 daysAir Mass ThunderstormsBy far, the greatest number of thunderstorms on an annual basis worldwideRandom… not well organized… short lived (usually 1-1 ½ hour lifetimes)Ultimately the downdraft (colder, more dense air) cuts off the updraft and the storm commits atmospheric suicideTopographically/geographically/daytime heating relatedBy definition within an air mass (mT)Severe ThunderstormsWhat makes a thunderstorm severe?Presence of a tornado1 inch or larger diameter hail (at the surface)Convective wind gusts of 50 knots/58 miles per hourLess than 5% of all thunderstorms are considered to be severeLess than 1% of all thunderstorms produce tornadosLonger lasting because of an established/well developed wind structure (2 hours or longer)Most severe thunderstorms occur in the middle latitudes along the cold fronts/dry lines (cP/mP/mT/cT boundaries)Important Ingredients Needed for Severe Thunderstorm DevelopmentMore than marginally unstable airStrong lifting mechanisms (fronts, cyclones)Air flow aloft to encourage strong updrafts (wind speed shear and wind direction shear as you go further aloft)Wind veers with heightVeering—when winds shift clockwise with height, time, etc.Backing wind—opposite of veering wind, shifts counterclockwise with time, height, etc.The presence of an initial temperature inversion???Stable air aloft trapping warm air below itAssumption is that you will be able to explosively get rid of that inversion as the front/dry line moves through itInversion acts like a balloon when you blow it up and when you pop it the whole balloon explodes…that is the way the atmosphere isWhen you have severe weather and an inversion you want to make sure it popsSquall LinesA line of thunderstormsDensity of thunderstorms along the line can determine the severity of the individual thunderstormsDon’t have to be solid, you can have little spaces between each onemT air mass because moisture is importantThunderstorms compete for the moist, unstable airBroken squall line—when storms are still closely backed