Download Forecasting Checklist - Atmospheric Sciences at UNBC

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
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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/.
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