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ENSC408/608ForecastingResources Winter2016 ForecastingChecklist Thisisageneralchecklistthatcanbeusedinmakingroutineforecasts. 1. Willcloudcoverplayanimportantroleinyourtemperatureforecast? Cloudinessduringthedayblockssunshineandtendstokeeptemperatureslower.Nighttime cloudinessincreasesincominglongwaveradiationandreducesradiativeheatlossfromthe surface,whichmakesovernighttemperatureswarmer.Thethickertheclouds,themoreeffectit willhave. 2. Willtemperatureadvectionplayanimportantroleinyourtemperatureforecast? Ifthewindsatthesurfaceorat850hPaareblowingfromanareawithmuchwarmerorcooler temperatures(acrossthetemperatureorthicknesscontourlines),thenitwillhelptomovethat airmassintoyourlocation.Ifthewindsarestrongenough(greaterthan10or15knots),this couldhaveasignificantwarmingorcoolingeffectonyourtemperatures. 3. Willfrontsplayanimportantroleinyourtemperatureforecast? Ifacoldfrontmovesthrough,youcanexpectcoolertemperaturesbehindit.Anyprecipitation willusuallyoccurinclosevicinityofthefront.Ifawarmfrontmovesthrough,expectwarmerair behindit.Precipitationisnormallyaheadofthefront,butoveralargearea.Stationaryfronts cansometimescauseprecipitation,buttheywillnotaffectyourtemperatureforecastunless theyareveryclosetoyourlocation. 4. Istheresufficientmoisture(fromsurfaceto850hPa)forprecipitationtooccur? Ifthereismoistureavailable,isthereaforcingmechanismtoliftit? Dewpointisagoodindicatorofmoistureintheatmosphere.Ifthereislessthana10°C differencebetweentheairtemperatureandthedewpointtemperature,thenyouwould considertheremaybesufficientmoistureforprecipitation.Relativehumidity(RH)mayalsobe used.Inorderforprecipitationtooccur,however,thisairhastobeliftedforthemoistureto condense.Goodforcingmechanismsincludebutarenotlimitedtofronts,vorticity,divergence intheupperatmosphere,andconvergencenearthesurface. 5. Istherevorticityat500hPa? Vorticityreferstoatypeofrotatingmotionintheatmosphere.Themovementofhighandlow areasofvorticityat500hPacanbeagoodindicatorforwhereupwardanddownwardmotion willoccur.Ifanareaofhighvorticitywillmovingintoyourlocationinthenext12hoursorso, thenyoucanexpectupwardmotiontooccuraheadofit.Conversely,ifanareaoflowvorticityis 1 ENSC408/608ForecastingResources Winter2016 approaching,thenyouwillexperiencedownwardmotion.Cloudsandprecipitationrequire upwardmotion–solookforweathertooccurwherevorticityisincreasing. 6. Arethereanyshortwavesat500hPa? Shortwavescanbeobservedassmall"kinks"intheflowoftheatmosphere(lookatthecontour linesandvorticitycontourstofindwheretheyare).Youcanexpectupwardmotiontooccurin areaswherethesearelocated. 7. Isthejetstreamat250hPapositionedfordevelopment? Ifyoudividetheareaofhighestwindsinthejetstreamintofourquadrants,theleftexitand rightentrancesectionsarethemostfavorableareasforupwardmotionandprecipitationto occur.Therightexitandleftentrancesectionssupportdownwardmotionandarenotgoodfor precipitation. Resourcestouseformakingforecasts 1. UsetheWeatherViewerpageasastartingpoint.http://cirrus.unbc.ca/wxv. a. ANALYSIShasweathermapsat250hPa(jetstream–approx10km),500hPa(thickness– approx5km)andSurface(fronts),aswellasat850hPa(temperature–approx1.5km)and 700hPa(temperature,moisture–approx3km) b. SATELLITEhassatelliteimages.TheAlaskasectorisparticularlygoodforourarea. c. RADARisusefulforshort-rangeprecipitationforecasting–XPGisthePrinceGeorgeradar. d. VERT-PROFILEhasradiosonde(weatherballoon)data.CZXSisthePrinceGeorgestation. e. PROGNOSIShasnumericalweatherpredictionmodeloutputs 2. Otherresourcescanbefoundathttp://cirrus.unbc.ca/common/wxref.html 3. YouwillbedevelopingyourownsetofresourcesinLab1.Thesewebpagesfromeveryonewillbe madeavailableonlineathttp://cirrus.unbc.ca/wiki/. 2