Polar Vortex in North America

 

For the 2014 extreme weather event, see 2014 North American cold wave.
 

A polar vortex (also known as a polar cyclone, polar low, or a circumpolar whirl) is a persistent, large-scale cyclone located near either of a planet's geographical poles.

On Earth, the polar vortices are located in the middle and upper troposphere and the stratosphere. They surround the polar highs and lie in the wake of the polar front.
These cold-core low-pressure areas strengthen in the winter and weaken in the summer due to their reliance upon the temperature differential between the equator and the poles.
 They usually span less than 1,000 kilometers (620 miles) in which the air is circulating in a counter-clockwise fashion (in the Northern Hemisphere).
As with other cyclones, their rotation is caused by the Coriolis  effect

polar vortex and subsequent southward movement of tropospheric Arctic air was caused by sudden stratospheric warming (SSW), a phenomenon discovered in 1952. NASA states, "A major midwinter SSW event occurs when polar stratospheric temperatures increase by at least 25 K in one week, and the zonal-mean zonal wind at or near 10 hPa (at about 30 km altitude) reverses direction and becomes easterly north of 60° N.

For more details
refer Wikipedia