"It's brutally cold, definitely brutal," meteorologist Tony Zaleski said.
Slick roads were blamed for scores of accidents. In Indiana, a driver was reported killed in a crash with a school bus near Delphi on Thursday. In Iowa, a driver died Wednesday after slamming into the back of a semitrailer that had slowed for an accident near Des Moines.
In preparation for worsening conditions, more than 500 flights were grounded at Chicago's airports. The Chicago Department of Aviation reported more than 400 canceled flights at O'Hare International Airport and more than 100 canceled flights at Midway International Airport. In Atlanta, Delta Air Lines canceled nearly 200 flights scheduled to leave after 5 p.m. Thursday in anticipation of snow. Frost on planes' wings delayed seven early flights in Tampa, Fla.