ST. LOUIS, Mo. – — A large section of the U.S. braced Tuesday for a big winter storm that was forecast to drop heavy snow in the Rockies, ice highways, disrupt travel in the Midwest, and plummet temperatures below freezing in Texas.

Airlines had canceled more than 800 flights in the U.S. scheduled for Wednesday, the flight-tracking service revealed, 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 do virtual classes this week. MoDOT held a press conference today pushing firms to have workers complete their jobs remotely, if possible.

Winter storm watches and warnings covered a vast region of the US from El Paso, Texas, through the Midwest and parts of the Northeast to Burlington, Vermont. The storm follows a devastating nor’easter that delivered blizzard conditions to several portions of the East Coast.

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

During the multiday storm this week, some places may get a combination of rain and freezing rain before it transitions to snow.

“It will be a really nasty 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 area of the state prepared for heavy snow, ice and severe wind gusts in the region.

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

On Wednesday and Thursday, the weather service warned 8 to 14 inches (20 to 36 cm) of snow was possible in regions of Michigan, including Detroit. From Wednesday through Friday morning, 9 to 14 inches (23 to 36 centimeters) of snow was anticipated in northeastern Ohio.

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

“We could see some power outages, but, it’s also recommending that they be limited in scale and character and extremely short term in duration,” Kralicek added.

Becky Gligo, director of the group Housing Solutions in Tulsa said teams are working to get homeless people into shelters ahead of nightly lows that are forecast to plummet into single digits by Friday night.