The National Weather Service's map, pasted below, charts how temperatures plunged overnight. (And in Forbes: The Advisory Board's Dan Diamond and Graham McLaughlin discuss how to help the homeless through the cold snap.)
The alarming weather put hospitals from Chicago to Atlanta on high alert.
"When you are responsible for the care of patients," said Temple University Hospital President and CEO John Kastanis, "You have to be ready for the worst possible situation at all times."
Kastanis said his Philadelphia-based hospital implemented the first phase of its emergency preparedness plan as temperatures began to fall last week.
In the Twin Cities, where temperatures dropped as low as 23 below zero, Regions Hospital had treated a "record-breaking" eight patients for hypothermia and 14 for frostbite as of early Monday evening. At UW Health in Madison, Wis., about half a dozen patients were treated for frostbite, while nearby Meriter also reported a handful of cases.
For emergency responders, the cold has created a serious obstacle in efforts to get injured patients to area hospitals. "Days like this, you dress a little bit warmer, but the problem is you cannot dress too warm because we are in and out all the time," says Dick Carpenter, an Allina paramedic.
Stay safe. Before going outside, check out these doctors' tips for surviving the record-breaking cold weather.