This Is Why It Was So Insanely Cold Last Month

That incredibly cold, it-hurts-to-be-outside weather that much of the U.S. experienced last month may come back to bite the country again next week.

So what's causing these temperature extremes?

The polar vortex is a mass of winds that form over the Arctic each winter, and tend to move in a circular motion around the region, according to NASA. This year, however, a few factors caused the vortex to dip south, like the jet stream moving further south than usual and a low-pressure system forming over Canada, according to the video.

As this animation progresses from early December 2013 to early January 2014, you can watch the polar vortex -- represented by the purple colors -- bend southward over time. It features data collected by NASA's Atmospheric Infrared Sounder Mission instrument, and shows temperatures at 3,000 feet above the Earth's surface.

As NASA points out on their website, this year's cold wave set many temperature records. And that wasn't all: flights were canceled, Canada experienced frost quakes and a jail escapee returned to prison because it was so cold.