What is the polar vortex?

The frigid air will come from a brief visit by the polar vortex — which is a real meteorological phenomenon, not just a sensational headline. It’s a whirling mass of cold air circulating in the mid- to upper-levels of the atmosphere, present every winter.

It usually stays closer to the poles but sometimes breaks apart, sending chunks of Arctic air southward into the U.S. during winter.

This week’s particularly cold…