The National Weather Service (NWS) forecast temperatures between -10 to -40 degrees Fahrenheit (-23 to -40 Celsius) by Wednesday, with wind chill making it seem as cold as -65 degrees Fahrenheit in one area of Minnesota.
The culprit was a lobe of arctic air that has broken away from the polar vortex that usually encircles the North Pole. "A record cold air mass will continue into the central and northern US, spreading to the east coast on Tuesday," the NWS said. "Wind chills of -30 to -60 (Fahrenheit) can be expected over portions of the northern Plains and Great Lakes region."
Michigan and Wisconsin declared statewide emergencies in advance of the frigid temperatures. Americans were heeding warnings to stay home if possible on Wednesday, when temperatures were expected to be at their coldest. Scores of schools, businesses and government agencies announced closures in multiple states.
"People exposed to extreme cold are susceptible to frostbite in a matter of minutes," warned the NWS. Lawrence Gottlieb of the University of Chicago Medical Center said the threat was significant "when temps fall below zero, especially when there is a strong wind."
More than 70 warming centers were opened in Chicago, America's third city, where temperatures were forecast to potentially rival or exceed the all-time record of -27 degrees Fahrenheit.
Wind chill would make the air feel closer to -40 to -50 degrees in the windy city, officials said. Minneapolis, Minnesota opened warming centers in government buildings and libraries, a 24-hour emergency shelter, and allowed residents to stay on public buses and trains for warmth.