You hear the StormTeam talk about the Polar Vortex, but what exactly is it?
The polar vortex is a strong area of low pressure at the surface and a cutoff low above the surface in the cold air of Canada. The vortex often moves very slowly or is stationary. The polar vortex weakens and can disappear during summer and it is usually the strongest during winter. The counterclockwise circulation around the vortex often pushes Arctic air south over the U.S.
The position of the vortex determines where in the U.S. the Arctic air will invade. When the vortex is centered over the Hudson Bay, the Arctic air usually plunges southward over the Dakotas and the northern Plains. If the vortex center shifts eastward, the core of the Arctic air invasion usually shifts eastward as a result. Other factors, such as a strong high pressure area to the west of the vortex, can enhance the southward plunge of Arctic air.