CHICAGO — Icy, snow-covered roads and high winds made travel treacherous Sunday from the Dakotas and Michigan to Missouri, as much of the nation faced another winter wallop: a dangerous and potentially record-breaking cold.
A whirlpool of frigid, dense air known as a polar vortex was expected to suppress temperatures in more than half of the continental United States starting into Monday and Tuesday, with wind chill warnings in place from Montana to Alabama.
It was 5 degrees at kickoff Sunday afternoon inside sold-out Lambeau Field in Green Bay, Wis., for the Packers’ and the San Francisco 49ers’ playoff game, 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. ‘‘Without the wind, which isn’t here yet, we’re good. When it gets windy, we’ll be ready for it.”
The forecast for overnight Sunday was extreme: 25 below zero in Fargo, N.D., 31 below in International Falls, Minn., and 15 below 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.
Several Midwestern states received up to a foot of new snow on Sunday. Five to 9 inches fell in the Chicago area by Sunday afternoon, the St. Louis area had about a foot of snow, and northern Indiana had at least 8 inches. Central Illinois braced for 8 to 10 inches, and southern Michigan could see up to 15 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.
Governor Mike Pence of Indiana ordered nearly 100 National Guard members to be ready to help rescue stranded motorists, move people to shelters, and assist local emergency services workers in reaching people who need medical help.
The state General Assembly postponed Monday’s opening of its 2014 session. Parts of Indiana were expected to get up to a foot of new snow.
In Chicago, temperatures were expected to bottom out around minus 15 overnight, probably 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.
Authorities also urged people to check on elderly and disabled relatives and neighbors.
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.
West, a Chicago native, 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 at a CVS pharmacy in nearby Berkley, Mich.
Travel problems started early Sunday. About 1,200 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 and Tennessee’s Memphis and Nashville international airports.
School was called off Monday for the entire state of Minnesota, as well as cities and districts in Wisconsin, Illinois, Indiana, and Iowa, among others. Chicago officials canceled classes Monday for the nation’s third-largest district.
Southern states are bracing for possible record temperatures, too, with single-digit highs expected Tuesday in Georgia and Alabama.
Temperatures are expected to dip into the 30s in parts of Florida on Tuesday. But Florida Citrus Mutual spokesman Andrew Meadows said it must be at 28 degrees or lower four hours straight for fruit to freeze badly.