What is a 'polar vortex' and why is it so dangerous?

A reader in South Elgin, Ill. takes out a bottle of water, only to see it freeze within 7 seconds.

“The Polar Vortex, a huge system of moving swirling air that normally contains the polar cold air, has shifted so it is not sitting right on the pole as it usually does,” Laden writes. “We are not seeing an expansion of cold, an ice age, or an anti

(CNN) — Americans in two dozen states from the Midwest to the Southeast and Northeast are shivering this week courtesy of a distorted polar vortex. The rush of cold air it's sending southward is the biggest visitor from the North Pole since Santa Claus.

As of Monday afternoon, the Midwest was battling uncommonly frigid weather that threatened to break some all-time-low temperature records. January is typically cold, but not this cold, with several Midwestern cities such as Chicago gripped by daytime 

Move over, haboob. See you next summer, heat dome. The weather phenomenon hogging all the attention now is.