"The dangerously cold wind chills could cause frostbite on exposed skin in as little as 10 minutes,” the National Weather Service warned.
The storm brought a dramatic change to a region that had experienced weeks of mild weather. In Milwaukee, temperatures climbed as high as 57 F (14C) on Wednesday, but were expected to drop into the teens, with wind chills below zero.
“It’s definitely going to be a shock to the system,” Paul Collar, a National Weather Service meteorologist, told the Milwaukee Journal Sentinel.
Highways were reopened in Minnesota after closing late Wednesday when winds blasted snow and hundreds of accidents were reported. Minnesota Gov. Tim Walz activated the National Guard late Wednesday to assist with accidents in two counties. On Thursday afternoon he authorized troops to provide assistance across the entire state.