Last winter was extremely mild except for about a week and a half in early February. Subzero weather during that time was initiated by a disruption of the polar vortex. A new study released in the journal, "Science," shows evidence that links an increase in these polar vortex disruptions to the warming climate of the Arctic region.
The polar vortex is a band of upper-level winds which normally form a tight circle around the Arctic. From time to time, this circulation weakens and becomes wobbly, allowing intrusions of bitterly cold air into the mid-latitudes. This new research shows that the still cold but rapidly warming arctic region is associated with an increase in these polar vortex disruptions. The increase in open Arctic waters and deeper Eurasian snow cover both help to provide the trigger. This explains the seemingly contradictory observations at our latitude of warmer winters in general combined with an increase in short bursts of extreme winter cold.