Bone-chilling temperatures caused by a "polar vortex" enveloped the nation's midsection Monday, with record lows closing schools, forcing the cancellation of thousands of flights and even freezing the engines of an Amtrak train for nine hours.
The icy blast — described by meteorologists as the worst in decades — is set to bring below-zero temperatures to more than half of the continental U.S. on Monday and Tuesday as it spreads east and south.
The Midwest and Plains have already endured temperatures as low as minus 30 degrees and wind chills that feel like minus 50 degrees.
Anyone venturing outside without wrapping up risked frost bite "in minutes or even seconds," according to Kevin Roth, lead meteorologist at The Weather Channel.
Illinois Gov. Pat Quinn urged people to avoid venturing outside unless absolutely necessary and to dress appropriately should they need to go out.
"This winter storm will be one for the record books and we want to make sure everyone stays safe and warm until it passes," he said in a statement Sunday night.
Passengers on an Amtrak train from Detroit to Chicago were stranded for more than nine hours after both the train's engines froze.
Valerie King, a journalism student at Chicago's Northwestern University, tweeted that she was "not exactly in the best of spirits." She said the train rolled in to Chicago at 1:20 a.m. local time on Monday.
Roth said the record low temperatures were being caused by the "polar vortex" shifting down from the Arctic. It was over Hudson Bay early Monday and isn't predicted to ease until Wednesday.
Roth said Tuesday will be the coldest day in the spell, with freezing temperatures forecast for parts of all 48 continental U.S. states.
This bitter air is set to reach the Mid-Atlantic region by Monday, before spreading to the Southeast and New England. The Tri-State area could see temperatures as low as 8 degrees on Tuesday, with New York City, Boston, and Washington, D.C., forecast fortemperatures of 14 to 18, according to The Weather Channel. Add in wind chills, and the "feels like" effect will be below zero.
Rain that fell across an area from Atlanta to Charlotte, N.C., created wet conditions on pavements and roads early Monday. As temperatures plummeted, this moisture was expected to turn to black ice on untreated surfaces, Roth said.
At least 10 inches of snow fell on parts of Illinois, Michigan and Indiana on Sunday. But by Monday, almost all of the snow showers were over, except for some lake-effect snow from northeast Ohio to southwest New York.
Schools were canceled across Minnesota, one of the coldest states. There were other closures across Wisconsin, Illinois, Indiana, and Iowa, The Associated Press reported.
Adding to the misery are power outages. More than 50,000 customers are without electricity in Indiana, Illinois and Wisconsin.
The mix of snow and bitter temperatures has severely affected air travel, with almost 14,000 flights due to come in or out of the U.S. canceled over the weekend. Another 2,500 scheduled for Monday were canceled by 5 a.m. ET, according to FlightAware.
Most of these, about 1,100, were at Chicago's O'Hare International Airport. But as the storm moved toward the Atlantic similar disruptions are expected at major East Coast hubs.
Flights were temporarily grounded for two hours at New York's John F. Kennedy International Airport on Sunday after a plane skidded off the runway and into a snow bank at 8 a.m. No one was injured.
One person died after a small private jet skidded on a runway while landing in Aspen, Colo., Sunday.
Sunday's NFC wild-card game between the Green Bay Packers and the San Francisco 49ers kicked off with temperatures at 5 degrees in Wisconsin. Wind chills hovered in the minus-teens.
--By NBC News.The Associated Press contributed to this report.