What is the 'polar vortex'?

AUSTIN (KXAN) -- A polar vortex has the potential to bring extremely cold temperatures to much of the lower 48 states.
It is "a large area of low pressure and cold air surrounding both of Earth’s poles," according to the National Weather Service. A counter-clockwise flow of cold air in the stratosphere forms the "vortex."Undisrupted polar vortex- stable cold air in the ArcticIn winter, the polar vortex can weaken and destabilize, causing it to dip southward and sending cold air into the mi