An Arctic blast gripped the northern Plains, Midwest and Great Lakes Saturday morning, with millions of Americans under freeze warnings.

Six million people were under winter alerts Friday from northern Minnesota into upstate New York, as snowfall totals downwind of lakes Erie and Ontario were expected to reach 3 feet or more.

The National Weather Service warned that the Arctic airmass is delivering the coldest temperatures since last winter. Wind chills in the northern Plains and upper Midwest…