The US Midwest dug out Monday from a snowstorm that closed schools and businesses, as millions braced for dangerous sub-zero temperatures that could shatter records.
School districts in Minnesota and Wisconsin canceled classes and government offices, universities and businesses shuttered, with the mercury expected to drop to a polar -40 Fahrenheit (-40 Celsius).
"Dangerously cold and potentially record breaking temperatures and wind chills are expected by Tuesday and Wednesday," National Weather Service (NWS) said.
"The arctic air, together with brisk winds, can lead to dangerously cold wind chill values."
In Wisconsin, where nearly a foot (30 centimeters) of snow was measured in one location, Governor Tony Evers declared a state of emergency, freeing up the Wisconsin National Guard for emergency work, if needed.
In North and South Dakota, peak wind gusts were measured at 60-70 miles (96-113 kilometers) per hour.
More than 1,000 flights were canceled at two airports in Chicago, a major regional hub and America's third largest city, in nearby Illinois.
On the heels of the storm, nearly a dozen states braced for a blast of arctic air known as a polar vortex, which was expected to lower temperatures well below normal and far below zero.
The frigid air mass had veered from its usual path and was forecast to fall into the Midwest beginning Tuesday. The chill was expected to bring temperatures to extreme lows by Wednesday and last through Thursday.
Temperatures were expected to plummet to between -10 to -40 degrees Fahrenheit in a vast area stretching some 1,200 miles from the Dakotas to parts of Ohio.
Wind chill would make temperatures feel more like -30 to -65 degrees Fahrenheit, according to NWS.
On Tuesday, the snow storm was expected to move to the northeast, where it could dump another 8 to 12 inches of snow in some areas.
In Wisconsin's biggest city, Milwaukee, downtown streets were virtually deserted Monday and every major highway in the state covered in ice or snow, according to the Milwaukee Journal Sentinel.
In Minnesota, numerous cities declared snow emergencies, the Minneapolis Star Tribune reported.
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