What’s a polar vortex and why is it menacing Michigan?

AstheGreatLakesregionbracesforapredictednear-recordcoldthisweekend,Michiganiansareagaincursingthedreaded“polarvortex.” Butwhatexactlyisthismeteorologicalmenace?AndwhyisitmakingMichigan’sunpredictablewinterweatherunbearable? TheanswerstartsattheNorthPole. Swirling,coldairfromtheArcticCircle(alsoknownasthepolarvortex)isusuallycontainedtothatpartoftheglobe.Buteverysooften,thesystemthatholdsitthereweakens,pushingitsouthward. “ThepolarjetstreamusuallycontainsthatArcticairtothenorth,”saidKevinKacan,ameteorologistattheNationalWeatherService’sDetroitregionaloffice.“Butwhenthere’sadisturbancethatbreaksthatnortherntrackofthejetstream,itallowsairtosinkdownintothenorthernU.S.” Inthiscase,expertssaidawarmupinEarth’sstratospheredislodgedapolar,low-pressuresystem,bringingfrigidairfromtheNorthPolesouthward. IntheDetroitregion,themeteor