What's a Polar Vortex?: The Science Behind Arctic Outbreaks

One of several semi-permanent weather systems over the Earth, the polar vortex is an area of low pressure in the upper atmosphere that, on average in the Northern Hemisphere, typically has centers in two main areas: near Canada's Baffin Island, and over northeast Siberia...Occasionally, the polar vortex can either be forced well south of its typical position, or a significant piece of the larger spin can break off and plunge south into the U.S....In essence, instead of cold, Canadian air grazing the northern tier of the U.S., then draining off into the north Atlantic Ocean, the heart of this Arctic air plunged south into the U.S.