What is a polar vortex?

A blast of Arctic air is expected to push across many regions of North America this week, including the U.S. east coast. Last winter, meteorologists referred to the dreaded "polar vortex" as temperatures plunged to punishingly low levels. Some theorized the cold snap was linked to the weakening of a polar vortex spinning above the North Pole.

As shown in the graphic below, some scientists suggestedthat cold air spills out of the weakened whirlpool above the Arctic. The cold air then travels south across North America. The U.S. National Oceanic and Atmospheric Administration notes, however, that extreme winter weather is often influenced by a host of atmospheric factors.