Who has ever heard of a polar vortex?
So basically, this phenomenon is what's to blame for the extreme cold we're experiencing. The graphic you see below was found at the Washington Post. You can read more about this at the LA Times. Here's hoping you're safe and warm. And of course call 311 if you need to find a warming center. Check Chicago Weather Center for current temps and of course here's Tom Skillings seven-day forecast.