After a warm autumn and mild start to December the “polar vortex weather pattern” made famous during winter 2013-14 and 2014-15 but absent the last 2 winter season’s makes a bold return. Evolution of this pattern arrives late this week and becomes established during the middle third of December. After the mild temperatures of late autumn and early meteorological winter this air mass will feel cold!
Initially, the relative warm Great Lakes moderate the air mass especially in the Midwest/Great Lakes/Northeast U.S. However, in time the Great Lakes temperatures cool dramatically and early season ice forms and expands. Lake-effect snows widen and snow cover spreads throughout the Northeast piling deep downwind of the Great Lakes to the mountainous Northeast.
The 15-day snowfall forecast by the European ensemble indicates snow cover could dip southward to northeast Georgia and extend to the Mid-Atlantic Coast with several inches on the ground inland to a foot or more in parts of the Great Lakes and New England. The evolving snow cover helps to sustain and intensify the cold effect of the polar vortex with time.
Heavy snows are also likely in the Upper Midwest. A blizzard warning is in effect now for the eastern Dakotas.