A collapse in the polar vortex is letting Artic air come here. What that means, and why it happens.

As the U.S. prepares to take on another bout of cold weather, the term "polar vortex" is getting thrown around. But what is it?

Despite being notorious for bringing brutal cold and dangerous wind chills, the polar vortex has a surprising upside.

A polar vortex expansion is bringing extreme cold and heavy snow to over 150 million Americans across two dozen states.