Cold Front | SKYbrary Aviation Safety

Fronts are usually hundreds of miles long. A cold front forms when a cold, dense air mass pushes under a warm, lighter air mass, forcing the warm air to ... Skiptomaincontent Youarehere Home » Portals » OperationalIssues » Weather ColdFront ColdFront ArticleInformation Category: Weather Contentsource: SKYbrary Contentcontrol: SKYbrary Description Whenlargemassesofwarmairandcoldairmeet,theydonotmixbecauseofdensitydifferences.InWorldWarI,meteorologistsinthe“NorwegianSchoolofMeteorology”referredtothisboundaryasa“front”,amilitaryanalogytoabattlelinewhereinthiscasethewarmandcoldairmasseswere“fighting”forsupremacy. Frontsareusuallyhundredsofmileslong.Acoldfrontformswhenacold,denseairmasspushesunderawarm,lighterairmass,forcingthewarmairtorise.Thecoldairadvances,replacingthewarmairatthesurface.Rainandeven thunderstorms canformasthemoistureinthewarmairmassrises,cools,andcondenses.Withacoldfrontalpassage,thewindswilltypicallyshiftfromthesouthtothewestornorth.Asthefrontmovesthrough,cool,fairweatherislikelytofollow. Thetemperaturesbehindacoldfrontvarydependingonthetypeofairmassmovingin.Apolarairmasswillbringincoldairinthewinterandcoolairatothertimes.AnArcticairmasswillbeassociatedwithbitterlycoldtemperaturesinthewinter.Anairmasscomingoffhighlatitudeoceanareaswillbeunusuallycoldinsummerbutmoremoderateinwinter. ColdFront CloudtypesassociatedwithaColdFront Ifthecoldfrontishighlyunstable,cumulonimbuscloudsproducingthunderstormscommonlyformalongoraheadofthefront.Anvilcirruscloudsmayspreadaconsiderabledistancedownwindfromthethunderstorms.Theothercloudtypesassociatedwithacoldfrontdependonatmosphericconditionssuchasairmassstabilityandwindshear.Asthefrontapproaches,altostratusandlow-levelstratocumuluswithintermittentlightprecipitationmayformifthewarmairmassbeingdisplacedbythecoldfrontismostlystable. Afterthepassageofthecoldfront,theskyusuallyclearsashighpressurebuildsinbehindthesystem,althoughsignificantamountsofcumulusorstratocumulus,oftenintheformoflongbandscalledcloudstreetsmaypersistiftheairmassbehindthefrontremainshumidfromasourceofmoisture.Smallandunchangingamountsofcumulusorcirruscloudsinanotherwiseclearskyareusuallyindicationsofcontinuingfairweatheraslongasthebarometricpressureremainscomparativelyhigh. Precipitation Theamountofprecipitationassociatedwithacoldfrontdependsontheamountofmoistureintheairandtheamountofliftingthefrontproduces.Youneedbothabundantmoistureandstrongliftingtoproducesignificantprecipitation.Sometimesbandsofprecipitationcanoccurwellaheadofthefrontespeciallyifthewarmairmassisunstable. Thecoldfrontitselfcommonlybringsanarrowbandofprecipitationthatfollowsalongtheleadingedgeofthecoldfront.Thesebandsofprecipitationcanbeverystrongandcanbringseverethunderstorms,hailstorms,snowsqualls,and/ortornadoes.Inthespring,thesecoldfrontscanbeverystrong,andcanbringstrongwindswhenthepressuregradientishigherthannormal.Coldfrontssometimescomethroughanareawithlittleornoprecipitation.Thesedrycoldfrontscancausewildfirecontrolproblems.Widerrainbandscanoccurbehindsomeshallowcoldfrontswhichtendtohavemorestratiform,andlessconvective,precipitation.Theserainstormssometimesbringflooding,andcanmoveveryslowlywhenthestormsteeringitisstrongandembeddedwithinameridionalflowpattern(withmorepoletoequatormotionratherthanwesttoeastmotion).Ifthelow-levelcoldairbehindsuchafronthasbelowfreezingtemperatures,icestormsduetofreezingrainarepossible. Inthewinter,coldfrontscanbringcoldspells,andoccasionallysnow.Inthespringorsummerintemperatelatitudes,hailmayoccasionallyfallalongwiththerain.Ifmoistureisnotsufficient,suchaswhenasystemhaspreviouslymovedacrossamountainbarrier,coldfrontscanpasswithoutcloudiness. Frontalsnowsqualls Snow-coveredsurfaces Acoldfront,canproducefrontalsnowsqualls—anintensefrontalconvectiveline,whentemperatureisnearfreezingatthesurface.Thestrongconvectionthatdevelopshasenoughmoisturetoproducewhiteoutconditionsatplaceswhichlinepassesoverasthewindcausesintenseblowingsnow.Thistypeofsnowsquallgenerallylastslessthan30minutesatanypointalongitspathbutthemotionofthelinecancoverlargedistances.Frontalsquallsmayformashortdistanceaheadofthesurfacecoldfrontorbehindthecoldfrontwheretheremaybeadeepeninglow-pressuresystemoraseriesoftroughlineswhichactsimilartoatraditionalcoldfrontalpassage.Insituationswheresquallsdeveloppost-frontallyitisnotunusualtohavetwoorthreelinearsquallbandspassinrapidsuccessiononlyseparatedby25miles(40kilometers)witheachpassingthesamepointinroughly30minutesapart.Incaseswherethereisalargeamountofverticalgrowthandmixingthesquallmaydevelopembeddedcumulonimbuscloudsresultinginlightningandthunderwhichisdubbed"thundersnow". Depictiononweathermaps Onweathermaps,thesurfacelocationofacoldfrontismarkedwithabluelineoftrianglespointinginthedirectionofthefront. AmaturelowpressuresystemshowingawarmfrontaheadofthewarmmidlatitudeairmassstreamingtowardsthePolewhereitmeetsthecoldpolarairmass RelatedArticles ExtratropicalCycloneModels WarmFront LakeEffectSnow StationaryFront Categories Weather, WeatherPhenomena Feedback SKYbraryPartners: Safetyknowledgecontributedby: JoinSKYbrary IfyouwishtocontributeorparticipateinthediscussionsaboutarticlesyouareinvitedtojoinSKYbraryasaregistereduser Contactus MessagetotheEditor AboutSKYbrary WhatisSKYbrary Copyright©SKYbraryAviationSafety,2021-2022.Allrightsreserved.