CHICAGO - A powerful storm dumped mounds of snow across the upper Midwest Sunday, closing major highways, forcing cancellation of 1,600 airline flights in Chicago, and collapsing the roof of the Minnesota Vikings' stadium.

At least four weather-related deaths were reported as the storm dropped nearly 2 feet of snow in parts of Minnesota and marched east.

A blizzard warning was in effect Sunday for parts of eastern Iowa, southeastern Wisconsin, northwestern Illinois, and northern Michigan, according to the National Weather Service. Surrounding areas, including Chicago, were under winter storm warnings. Much of Iowa was under a wind-chill advisory.

In Minneapolis, the heavy snow left the Metrodome decidedly unready for football. Video from inside the stadium, telecast by Fox Sports, showed the inflatable Teflon roof sagging before it tore open, dumping large amounts of snow at one end of the playing field.

No one was hurt, but the Vikings' game against the New York Giants, previously rescheduled to Monday, had to be moved to Detroit's Ford Field.

At least 1,375 flights were canceled at O'Hare International Airport, and more than 300 were canceled at Midway International Airport, said Karen Pride, a spokeswoman for the Chicago Department of Aviation. Both airports reported significant delays.

Officials at O'Hare set up about 200 cots, and Pride said amenity kits containing toothpaste and toothbrushes would be provided to any travelers stranded at the airport.

Illinois State Police closed a section of I-80 in the north-central part of the state after a pileup west of Peru, and part of I-55 near Springfield after accidents and reports of zero visibility. No deaths were reported.

Seven vehicles crashed on I-94 about 50 miles west of Milwaukee, prompting authorities to close the westbound lanes. A vehicle lost control on an ice-covered road and slammed into a tree in southeastern Wisconsin, killing a 21-year-old.

In Iowa, I-29 from the state line to Sioux Falls, S.D., remained closed, although other portions of I-29 and I-80 were reopened.