The polar vortex has been in the news again because it is contributing to the cold conditions we have been experiencing in the Southeast recently. But there is still a lot of confusion about what it is and how it has come to affect us here. PBS/Nova has a very interesting discussion of how there are really two different definitions of the polar vortex and how it has changed over time. You can read the article here. It quotes a couple of my friends from grad school days in Wisconsin, Jon Martin and Steve Vavrus.

Visualization of stratospheric polar vortex on Dec. 18. (earth.nullschool.net)