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ST. LOUIS, Mo. – — A huge swath of the U.S. braced Tuesday for a major winter storm that was expected to dump heavy snow in the Rockies, ice highways, disrupt travel across the Midwest, and plunge temperatures below freezing in Texas.

Airlines had canceled more than 800 flights in the U.S. scheduled for Wednesday, the flight-tracking service FlightAware.com showed, including many in St. Louis and Chicago.

Many St. Louis area schools have already canceled classes for Wednesday and Thursday. Others have decided to go remote and hold virtual classes this week. MoDOT held a press conference today urging employers to have workers do their jobs remotely, if possible.

See the full list of St. Louis area school closings here

Winter storm watches and warnings covered a wide swath of the country from El Paso, Texas, through the Midwest and parts of the Northeast to Burlington, Vermont. The storm follows a vicious nor’easter that brought blizzard conditions to many parts of the East Coast.

Canceled flights began to mount Tuesday, with St. Louis leading the list with more than 60% of its scheduled departures for Wednesday canceled. Chicago O’Hare International Airport canceled about 90 of its departing flights, and airports in Kansas City and Detroit were also canceling more flights than usual.

During the multiday storm this week, some areas may see a mix of rain and freezing rain before it changes to snow.

“It will be a very messy system and will make travel very difficult,” said Marty Rausch, a meteorologist with the National Weather Service in College Park, Maryland.

Illinois lawmakers canceled their three scheduled days of session this week as the central part of the state prepares for heavy snow, ice and high wind gusts in the region.

The National Weather Service said 6 to 12 inches of snow was expected by Thursday morning in parts of the Rockies and Midwest, while heavy ice is likely from Texas through the Ohio Valley.

On Wednesday and Thursday, the weather service said 8 to 14 inches (20 to 36 centimeters) of snow was possible in parts of Michigan, including Detroit. From Wednesday through Friday morning, 9 to 14 inches (23 to 36 centimeters) of snow was forecast in northwestern Ohio.

In Tulsa, Oklahoma, where up to 7 inches of snow and sleet are forecast but little ice, emergency management director Joe Kralicek said the event is not expected to cause large-scale power outages based on an ice index used by the National Weather Service.

“We could see some power outages, however, it’s also suggesting that they be limited in scope and nature and very short term in duration,” Kralicek said.

Becky Gligo, director of the nonprofit Housing Solutions in Tulsa said teams are working to move homeless people into shelters ahead of overnight lows that are expected to drop into single digits by Friday night.