What is a polar vortex?

Most of the Midwest is bracing for dangerously cold temperatures this week caused by something called a polar vortex.

A polar vortex is basically a large low-pressure system – a wide area of swirling cold air -- that is parked over the polar regions, according to the National Atmospheric and Oceanic Administration (NOAA).

"The term "vortex" refers to the counter-clockwise flow of air that helps keep the colder air near the poles, the National Weather Service said on its website, but when it strays south, it can cause brutal weather conditions in the U.S., including sub-zero temperatures.

In the winter, the polar vortex expands or migrates, which happens fairly regularly, and forces frigid air southward. Parts of the system have even reached as far south as Florida in years past, NOAA officials said.

During winters with long periods of freezing cold weather, scientists say the polar vortex is usually to blame.

Polar vortexes are not new, according to the NWS, it's just that they've been getting more attention in recent years. It's a weather feature that has always been around.

When you hear the term “polar vortex” it just means get ready for frigidly cold conditions.