Holiday travelers in the Upper Midwest scrambled Sunday to make it home ahead of a major winter storm bringing heavy snow, strong winds and travel headaches to a wide swath of the region, including Chicago's O'Hare and Midway airports.

The storm produced blizzard conditions in the hardest-hit areas Sunday, forecast to be the busiest travel day of the Thanksgiving weekend.

Widespread snow of 6 to 12 inches was expected from the Middle Mississippi Valley to the Great Lakes, the National Weather Service warned. Parts of Illinois experienced whiteout conditions, 45 mph gusts and up to 2 inches of snow per hour.

Heavy snow hit the Chicago Metro area later Sunday, triggering nearly 800 flight cancellations and at least 446 flight delays at O'Hare International Airport, a major hub. Airline delays in or out of Chicago had a ripple effect throughout the nationwide system.

Nationwide, 1,777 flights had been canceled and 4,867 delayed as of 10:45 p.m. EST, according to flight-tracking service FlightAware. Most of the cancellations were in Chicago and Kansas City. Dallas-Fort Worth, Denver and Boston were among other airports hit. The weather led most major airlines to waive change fees.

"It has been snowing for awhile in the Rockies, but it's headed to Chicago," said AccuWeather senior meteorologist Paul Walker.

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The snow dropped almost 10 inches in parts of Idaho and Wyoming on Saturday night into Sunday. Jackson, Wyoming, was hit with 9 inches.

Walker said blizzard and near-blizzard conditions are likely from Topeka, Kansas, and Omaha, Nebraska, to Des Moines, Iowa, and Madison, Wisconsin. Major interstates to small backroads could see hazardous driving conditions, he warned.

Kansas Gov. Jeff Colyer declared a statewide disaster emergency. Parts of Interstate 70 were ordered closed in the state.

"The Kansas Department of Transportation has reported multiple road closures due to visibility," Colyer said. "We strongly recommend you postpone travel plans due to the conditions if possible."

In Nebraska, parts of I-80 were closed as snow and crashes snarled the highway.

A mix of freezing rain, sleet and snow in Washington could cause hazardous driving conditions through Tuesday morning, the National Weather Service said. Up to 8 inches of snow is likely in the Cascades.

The fast-moving storm is likely to drop heavy snow on parts of New England by Tuesday, a foot or more in northern New Hampshire and Maine. Temperatures will plummet Monday and Tuesday from the Ohio Valley to the East Coast. Conditions could be as much as 15 to 30 degrees below normal, especially in the middle Mississippi Valley and parts of the Ohio Valley.

Contributing: Ben Mutzabaugh and Kristin Lam