Aside From Really Cold, What's A Polar Vortex?

Just two weeks after Santa Claus made his annual journey to points south, another visitor from the North Pole has arrived in the United States bringing record-breaking subfreezing temperatures.

A gigantic mass of swirling dense air known as a "polar vortex" has traveled from the Arctic, allowing Americans who had no plans of visiting the North Pole to "experience true arctic air," said Tom Kines, a senior meteorologist at Accuweather.

"Essentially, the polar vortex sits up around polar region. It's the cold air up there. That whole air mass has pushed southward towards the northern tier of the United States," Kines told

A visit from the polar vortex "doesn't happen every year and doesn't always pushed this far south," said Kines, but it's a regular part of the Earth's weather and has "happened in the past and will happen in the future."

The good news: The vortex won't stay long in the U.S. Already, it's starting to retreat back to the arctic.

For the meantime, though, temperatures are dangerously cold. The mercury dropped to 32 below in Fargo, N.D., and minus 21 in Madison, Wisc.