Tom Niziol, a winter weather expert for The Weather Channel, said the South was in for weather "that many parts have not seen in years" — perhaps the biggest winter weather event in a generation.
It was too early to say just how much snow could fall overnight and into Tuesday, but forecasters were warning that if all of the precipitation falls as snow — instead of sleet — more than 6 inches was possible in a region that rarely sees it.
"We're very concerned about a potentially crippling snowstorm for southeast Georgia and the Lowcountry of South Carolina," Wiltgen said.
At the same time, the Great Lakes shivered yet again under wind chills that approached 50 degrees below zero. School officials in major cities across the region — Cleveland, Cincinnati and Columbus, Ohio; Chicago; Milwaukee and Madison, Wis.; Detroit; Minneapolis and Duluth, Minn.; and Indianapolis — said classes would be canceled Tuesday.
"We're going to be talking about some seriously cold mornings," with temperatures as much as 35 degrees below normal for what is already historically the coldest time of the year, Weather Channel meteorologist Alex Winter said.
Lows overnight into Tuesday were forecast to plummet to 5 degrees below zero in Detroit and 20 below in Chicago, where school was already called off for Tuesday and whose airports scrapped more than 500 flights Monday.
A woman walking around Lake Harriet in Minneapolis on Sunday pauses to shoot some video of the blowing snow.
Up north, Minnesota took the brunt of the latest punishing blast of arctic air. Air temperatures dived lower than 20 below zero toward the Canadian border. Minneapolis woke up to 16 below, with a wind chill of minus-36.
Xcel Energy began telling about 100,000 customers in North Dakota, Minnesota and Wisconsin that they could crank their thermostats back up. They had been asked to keep their homes at 60 degrees after a natural gas shortage caused by a pipeline explosion in Canada over the weekend.
Still, the Anoka-Hennepin School District said it was closing based on a warning from the National Weather Service that wind chills would be severe enough to freeze exposed skin in five to 10 minutes.
For some school districts, it was the fourth cold-related closing this year.
A man waves to thank the driver of a passing car for giving he and a friend room on the road as they walk in Elkhart, Ind., during heavy snow Saturday.
"We've had a few people calling and emailing, saying, 'You know, it's Minnesota, get used to it,'" Mary Olson, a spokeswoman for the Anoka-Hennepin schools, told NBC station KARE. "But for the most part, people have been happy that we've closed."
The Northeast got a break, relatively speaking, at least for a day. New York snuck above freezing Monday morning, just enough to melt snow that has lingered on sidewalks since the middle of last week.
But the big cities of the Eastern Seaboard won't be spared for long. Forecast lows for Monday night were 9 degrees in New York, 9 in Philadelphia, 10 in Boston and 13 in Washington.