CHICAGO (AP) — Temperatures not seen in years are likely to set records in the coming days across the Midwest, Northeast and South, creating dangerous travel conditions and prompting church and school closures.

A "polar vortex" will affect more than half of the continental U.S. starting Sunday and into Monday and Tuesday, with wind chill warnings stretching from Montana to Alabama. The vortex is a counterclockwise-rotating pool of cold, dense air, and is behind the startling forecast: 25 below zero in Fargo, N.D., minus 31 in International Falls, Minn., and 15 below in Indianapolis and Chicago.

The bitterly cold temperatures already pushed into northern states Sunday morning. The National Weather Service reported a temperature of 9 below zero in Bismarck, N.D., and negative 21 at Duluth, Minn. At the height of the cold, wind chills may reach 50, 60 or even 70 below zero.

"It's just a dangerous cold," National Weather Service meteorologist Butch Dye in Missouri said Sunday morning.

Snow preceded the polar air and was expected to fall throughout much of Sunday from Michigan to Kentucky. Forecasts called for up to a foot in eastern Missouri and parts of central Illinois, several inches in western Tennessee and 1 to 3 inches in Kentucky.

Already, the weather created travel problems Sunday morning. In New York City, a plane from Toronto landed at Kennedy International Airport and then slid into snow on a taxiway. No injuries were reported, but the airport temporarily suspended operations for domestic and international flights because of icy runways.

Mike Duell, with flight-tracking website FlightAware.com, said Saturday to expect delays and flight cancellations because of the cold temperatures.

"For some of them, they run into limitations on the aircraft. They're only certified to take off at temperatures so low so if they get into a particular cold front it can prevent them from being able to legally take off," he said. "In a lot of cases, it's just ice."

The roads aren't much better in Missouri, where the state Department of Transportation warned that most major roadways were snow-covered, it was too cold for rock salt to be very effective and the wind was whipping.

"We're experiencing thunder snow and whiteout conditions," said MoDOT spokeswoman Marie Elliott. "If it gets to the point where it's no longer safe, we will consider suspending operations."

It hasn't been this cold for almost two decades in many parts of the country. Because of that, medical experts are reminding people that frostbite and hypothermia can set in quickly at 15 to 30 below zero, and it's key to be dressed for the temperatures.

"They have to wear a hat, they have to have face protection," said Dr. Brian Mahoney, medical director of emergency services at Hennepin County Medical Center in Minneapolis. He said mittens are better than gloves, layers of dry clothing are best, and anyone who gets wet needs to get inside.

"A person not properly dressed could die easily in those conditions," said National Weather Service meteorologist Scott Truett in St. Louis, describing the expected wind chill in Missouri at daybreak Monday.

Southern states are bracing for possible record temperatures, too. Meteorologists in central and north Georgia say temperatures could drop into the single digits by Tuesday, accompanied by wind chills as low as 15 degrees below zero.

Elsewhere, Minnesota has called off school Monday for the entire state — the first such closing in 17 years — as well as the Wisconsin cities of Milwaukee and Madison.

Sunday's NFL playoff game in Green Bay's Lambeau Field could be among one of the coldest ever played: A frigid minus 2 degrees when the Packers and San Francisco 49ers kick off around 3:30 p.m. Doctors suggest fans wear at least three layers and drink warm fluids — not alcohol.

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Associated Press reporters Jim Salter in St. Louis; Shelley Adler in Washington; Bill Draper in Kansas City, Mo.; Carson Walker in Sioux Falls, S.D.; and Brett Barrouquere in Louisville, Ky., contributed to this report.