A winter storm blanketed much of the central Midwest with snow on Sunday at the end of the Thanksgiving weekend, bringing blizzard-like conditions that grounded hundreds of flights and forced the closure of major highways on one of the busiest travel days of the year.

“It’s going to be messy,” said Todd Kluber, a meteorologist for the National Weather Service who is based in suburban Chicago.

With much of the central Plains and Great Lakes region under blizzard or winter storm warnings, more than 1,200 flights headed to or from the U.S. had been canceled as of 9 p.m. Sunday, according to the flight-tracking website FlightAware.

Most were supposed to be routed through Chicago or Kansas City — areas forecast to be hit hard by the storm.

Strong winds and snow created blizzard conditions across much of Nebraska and parts of Kansas, Iowa and Missouri. The National Weather Service was warning those conditions would make travel difficult in places.

By midday, the blizzard warning was extended to parts of eastern Illinois and Chicago, where snow is forecast to fall at a rate of about 2 inches per hour.

Other parts of the central Plains and Great Lakes region were under a winter storm warning that could see a foot or more of snow dumped in some places by the end of the day.

In eastern Nebraska, part of Interstate 80 between Lincoln and Omaha was closed Sunday morning because of multiple accidents after snow covered that area. That included semitrailer trucks jackknifed across the highway. It was re-opened by Sunday afternoon.

In Kansas, Gov. Jeff Colyer issued a state of emergency declaration. The action came as a large stretch of Interstate 70, spanning much of the state, was closed between Junction City and WaKeeney.

Separately, a portion of Interstate 29 was shut down in Missouri, near the Iowa border.

The weather service posted some snowfall totals on Twitter Sunday night. Kansas City International Airport got 5.3 inches of snow, and at least 7 inches of snow was reported in Rockford, Illinois.

As much as a foot was expected in Chicago. Forecasters predict more than a foot of snow is likely in southeast Nebraska, northeast Kansas, northwest Missouri and southwest Iowa.

By Monday morning, the storm was expected to hit parts of northern Indiana and southern Michigan.

Kluber said the storm was expected to hit the Chicago region sometime Sunday evening. He said rain will give way to heavy snowfall and “near whiteout conditions” that will make for dangerous travel.

Schools in parts of Kansas, Missouri, Iowa and Illinois have already called off classes for Monday.