MILWAUKEE -- Hundreds of schools and several large universities closed their campuses Tuesday as temperatures plummeted across the Midwest, with forecasters warning that the frigid weather will get worse and could be life-threatening.
The extreme cold and record-breaking temperatures are crawling into a swath of states spanning from North Dakota to Missouri and into Ohio after a powerful snowstorm pounded the region earlier this week.
Arctic air early Tuesday dropped temperatures in the Dakotas and Minnesota to as low as minus 27 degrees (negative 33 degrees Celsius), with wind chills as cold as minus 59 (negative 51 degrees Celsius)
"You're talking about frostbite and hypothermia issues very quickly, like in a matter of minutes, maybe seconds," said Brian Hurley, a meteorologist with the Weather Prediction Center.
Among the universities closed into Thursday are the University of South Dakota, Iowa State University and the University of Minnesota. Minneapolis Public Schools officials also cancelled classes through Wednesday, when the region is expected to experience frigidly low temperatures not seen in a quarter century. Hundreds of Michigan schools were closed Tuesday, including in Detroit, while Chicago Public Schools cancelled Wednesday classes because of the anticipated cold snap.
Closing schools for an extended stretch isn't an easy decision, even though most school districts build potential makeup days into their schedules to provide flexibility, said Josh Collins, spokesman for the Minnesota Department of Education.
"Many students, they might have two working parents, so staying home might mean they're not supervised," Collins said. "For some low-income students, the lunch they receive at school might be their most nutritious meal of the day."
Subzero temperatures hit some states Tuesday, but Wednesday is expected to be the worst. Wind chills in northern Illinois could fall to negative 55 degrees (negative 48 degrees Celsius), which the National Weather Service called "possibly life threatening."
Minnesota temperatures could hit minus 30 degrees (negative 34 degrees Celsius) with a wind chill of negative 60 (negative 51 degrees Celsius).
The potentially record-breaking low temperature forecast in Milwaukee is negative 28 degrees (negative 33 degrees Celsius), with a wind chill as low as negative 50 (negative 45 degrees Celsius). The current record of minus 26 degrees (negative 32 degrees Celsius) was set in 1996.
"That's 40 degrees below normal," Hurley said.
The unusually frigid weather is attributed to a sudden warming far above the North Pole . A blast of warm air from misplaced Moroccan heat last month made the normally super chilly air temperatures above the North Pole rapidly increase. That split the polar vortex into pieces, which then started to wander, said Judah Cohen, a winter storm expert for Atmospheric Environmental Research.
One of those polar vortex pieces is responsible for the subzero temperatures across the Midwest this week.
The Chicago Zoological Society said it was closing the Brookfield Zoo on Wednesday and Thursday -- marking only the fourth time the zoo has closed during its 85-year history -- to ensure the safety of its employees and animals. At O'Hare International Airport in Chicago, the high temperature Wednesday is expected to be negative 14 degrees (negative 25 degrees Celsius), which would break a record set on Jan. 18, 1994.
Homeless shelters were also preparing for the onslaught of cold. The Milwaukee Rescue Mission's call volume was "unusually high," but officials said there should still be enough beds for those who need them.
In Minneapolis, charitable groups that operate warming places and shelters were expanding hours and capacity "as they do whenever dangerous extreme temperature events occur," said Hennepin County Emergency Management Director Eric Waage. He said ambulance crews were handling all outside response incidents as being potentially life-threatening.
Chicago Mayor Rahm Emanuel said city agencies are making sure homeless people are in shelters or offered space in warming buses. He also urged residents to check on their neighbours and take safety precautions.
Cold weather advisories are in effect across a broad swath of the central U.S., from North Dakota to Missouri and spanning into Ohio. Temperatures will be as many as 20 degrees below average in parts of the Upper Great Lakes region and Upper Mississippi Valley, according to the National Weather Service.
On Monday, snowplow drivers had trouble keeping up with the snowfall in Minnesota and Wisconsin, where some areas got as much as 15 inches (38 centimetres) of snow.
Rare snowfall was also forecast for some southern states.
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Nicholson reported from Bismarck, North Dakota. Associated Press reporters Caryn Rousseau in Chicago, Gretchen Ehlke in Milwaukee and David Runk in Detroit, and AP Science Writer Seth Borenstein contributed to this report
