CHICAGO (AP) -- Icy, snow-covered roads and high winds made travel treacherous Sunday from the Dakotas and Michigan to Missouri as much of the nation braced for the next winter wallop: a dangerous cold that could break records.
A whirlpool of frigid, dense air known as a "polar vortex" was expected to suppress temperatures in more than half of the continental U.S. starting into Monday and Tuesday, with wind chill warnings stretching from Montana to Alabama.
It was 5 degrees at kickoff Sunday afternoon inside sold-out Lambeau Field for a playoff game between the Green Bay Packers and the San Francisco 49ers, one of the coldest ever played.
"We suited up, we brought all the snowboarding gear we use ... and added to it," said 49ers fan Jeff Giardinelli of Fresno, Calif.
A northwest wind made it feel like minus 10, and winds increased through the evening. But Giardinelli embraced the cold outside the game in a memorable outing that ended with his 49ers beating the Packers 23-20.
The forecast is extreme: 25 below zero in Fargo, N.D., minus 31 in International Falls, Minn., and minus 15 in Indianapolis and Chicago. Wind chills -- what it feels like outside when high winds are factored into the temperature -- could drop into the minus 50s and 60s. Northeastern Montana was warned of wind chills up to 59 below zero.
"It's just a dangerous cold," said National Weather Service meteorologist Butch Dye in Missouri.
Indianapolis Mayor Greg Ballard upgraded the city's travel emergency level to "red," making it illegal for anyone to drive except for emergency personnel, emergency purposes or seeking shelter. The last time the city issued such a travel warning was during the 1978 blizzard.
Several Midwestern states received up to a foot of new snow Sunday. The National Weather Service said snowfall at O'Hare International Airport in Chicago totaled more than 11 inches as of 6 p.m. Sunday -- the most since the Feb. 2, 2011, storm that shut down the city's famed Lake Shore Drive.
The St. Louis area had about a foot of snow and northern Indiana had at least 8 inches.
Officials closed several Illinois roadways because of drifting snow and warned residents to stay inside. Roads in the Midwest were particularly dangerous, and officials in Missouri said it was too cold for rock salt to be very effective.
Authorities also urged people to check on elderly and disabled relatives and neighbors.
In Chicago, temperatures were expected to bottom out around minus 15 overnight, likely setting a daily record, National Weather Service meteorologist Ed Fenelon said. Earlier Sunday, temperatures sank to minus 20 and colder in northern Minnesota and Grand Forks, N.D.
It hasn't been this cold for almost two decades in many parts of the country. Frostbite and hypothermia can set in quickly at 15 to 30 below zero.
Lorna West, a 43-year-old student and consultant from Columbus, Ohio, said she doesn't believe people unaccustomed to such weather are ready for what's coming.
A Chicago native, she said thermal underwear, lots of layers and "Eskimo coats" with zipped hoods to block the wind were the norm growing up.
"And don't go out if you don't have to," she said.
In Michigan, residents jammed stores to stock up on supplies.
"I made my husband go grocery shopping last night," said Kim Tarnopol, 46, of the Detroit suburb of Huntington Woods. Tarnopol was picking up cold medicine Sunday for her daughter Emma at a CVS in nearby Berkley, Mich.
Travel problems started early Sunday. In New York City, a plane from Toronto landed at Kennedy International Airport and then slid into snow on a taxiway. No one was hurt, though the airport temporarily suspended operations because of icy runways.
About 1,300 flights had been canceled Sunday at O'Hare and Midway international airports in Chicago, aviation officials said, and there also were cancellations at Logan International Airport in Boston, Tennessee's Memphis and Nashville international airports, and Lambert international airport in St. Louis.
School was called off Monday for the entire state of Minnesota, as well as cities and districts in Wisconsin, Illinois and Indiana and Iowa, among others.
Chicago Public School officials reversed course late in the day Sunday, canceling classes for Monday ahead of the expected bitterly cold temperatures. The change in plans came amid criticism from the Chicago Teachers Union, though officials say they made the decision after they "evaluated the situation again."
Southern states are bracing for possible record temperatures, too, with single-digit highs expected Tuesday in Georgia and Alabama.