Polar Vortex

A polar vortex refers to very large low-pressure areas centered over both the poles throughout the year. In the Northern Hemisphere, the jet stream, a current of fast moving westerly winds high in the atmosphere, encircles this feature and keeps the frigid air ‘trapped’ at the North Pole. Sometimes, the atmospheric conditions shift, which can cause the polar vortex to split and allow extremely cold Arctic air to flow into the U.S.

Source: NWS | NOAA | Washtington Post