Frigid air from the North Pole: What's this polar vortex?

Americans in two dozen states from the Midwest to the Southeast and Northeast are shivering this week courtesy of a distorted polar vortex...Much of the United States has plunged into a deep freeze from record low temperatures...It seems counterintuitive that global warming could cause significant cold snaps like this one, but some research shows that it could. We know that different types of extreme weather can result from the overall warming of the planet, melting of the Arctic Sea ice, etc. This includes extreme distortions of the jet stream, which can cause heat waves in summer and cold snaps in winter