Record low temperatures left at least a dozen dead as swirling winds usually found over the North Pole traveled south over the Great Lakes. Wind chill temperatures dropped as low as minus 55 Wednesday and Chicago was 10 degrees colder than Antarctica. Classes were canceled across the region, the U.S. Postal Service suspended deliveries and more than a thousand flights were grounded.
What about global warming? Despite a tweet by President Donald Trump suggesting that winter storms disprove it, scientists say rising average temperatures contribute to more extreme weather, including polar vortexes.