Heavy snowfall threatens to bring travel to a standstill. More than 1,000 flights canceled. Schools closed in Chicago, Detroit, Milwaukee.
The storm system, which stretches from Montana to Michigan, could drop up to 14 inches (36 cm) of snow in some areas, the National Weather Service said.
The heavy snow is forecast to move into upstate New York and New England by early tomorrow.
Wind chill temperatures are expected to drop below zero (below -18 C) in many areas.
The central and northern Rockies also will see heavy snow, the weather service said.