MILWAUKEE (AP) — Extremely cold, record-breaking temperatures are settling across parts of the Midwest after a powerful snowstorm pounded the region overnight Monday, and forecasters are describing the subzero weather on the way as potentially life-threatening.

Minneapolis Public Schools announced there would be no classes through Wednesday, when the region will experience frigidly low temperatures not seen in a quarter century.

“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.

The cold also prompted officials to close some schools in eastern Iowa, while Chicago Public Schools officials said they were monitoring the weather ahead of Wednesday’s cold snap. The Chicago Zoological Society, meanwhile, said it’s closing the Brookfield Zoo on Wednesday and Thursday to ensure the safety of employees and animals. It’s only the fourth time the zoo has closed during its 85-year history.

Subzero temperatures will begin 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 high temperature forecast at O’Hare on Wednesday is negative 14 degrees (negative 25 degrees Celsius), which would break a record set on Jan. 18, 1994.

Homeless shelters were preparing for the onslaught of cold. The Milwaukee Rescue Mission’s call volume was “unusually high,” but there should still be enough beds for those who need them, said the mission’s president, Pat Vanderburgh. Charitable groups that operate warming places and shelters in Minneapolis were expanding hours and capacity as the cold moved into the city where 1,500 people typically are sheltered on a given night.

“The charitable organizations responsible for operating shelters are adding emergency capacity as they do whenever dangerous extreme temperature events occur,” said Hennepin County Emergency Management Director Eric Waage. He said ambulance crews in the city were handling all outside response incidents as being potentially life-threatening.

Chicago Mayor Rahm Emanuel urged residents to check on their neighbors and take safety precautions. He said city agencies are making sure homeless people are in shelters or offered space in warming buses.

Cold weather advisories are in effect across a broad swath of the central U.S., from North Dakota to Missouri and spanning into Ohio.