A “polar vortex” pattern evolves in 10 days centered north of Minnesota and causing unseasonably cold temperatures and widening snow cover into the eastern U.S. Peak cold initiates Friday, Dec. 8 with temperatures averaging 10-20F below normal in Minnesota/Wisconsin/Illinois. While new snow cover enhances the cold in the Upper Midwest the shill also emanates a southern sprawl as departures from normal reach 5-10F below normal in the Gulf States that same day. Coldest departure from normal in the East is centered on Virginia Monday, Dec. 11 (about 10F below normal). During the polar vortex pattern south-central Canada snow cover deepens maintain the cold induced by the upper trough into mid-December while to the south where the ground is bare anomalous chill erodes Dec. 12-15.