AUSTIN, Texas (AP) — Airlines canceled hundreds of flights, governors urged residents to stay off roads and schools closed campuses as a huge swath of the U.S. braced for a major winter storm that was set to put millions of Americans in the path of heavy snow and freezing rain.

The approaching blast of frigid weather, which was expected to begin arriving Tuesday night, put a long stretch of states from New Mexico to Vermont under winter storm warnings and watches. More than a foot of snow was possible in Michigan, on the heels of a vicious nor’easter last weekend that brought blizzard conditions to many parts of the East Coast.

“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.

The projected footprint of the storm extended as far south as Texas, where nearly a year after a catastrophic freeze buckled the state’s power grid in one of the worst blackouts in U.S. history, Gov. Greg Abbott defended the state’s readiness. The forecast does not call for the same prolonged and frigid temperatures as the February 2021 storm and the National Weather Service said the approaching system would, generally, not be as bad this time for Texas.

“No one can guarantee that there won’t be any” outages caused by demand on the power grid, Abbott said Tuesday. “But what we will work to achieve, and what we’re prepared to achieve is that power is going to stay on across the entire state.”

In November, Abbott had, in fact, made a guarantee for winter: “I can guarantee the lights will stay on,” he told Austin television station KTBC.

Abbott, whose handling of last year’s blackouts is a top line of attack for Democrats as the Republican seeks a third term in 2022, said thousands of miles of roads in Texas will become “extraordinarily dangerous” over the coming days. Energy experts said the forecast this week, although below freezing, should not pose a challenge for Texas’ grid.

“The question has always been if we get a repeat of last year, would the power stay on? And this is nowhere near a repeat of last year,” said Doug Lewin, an energy consultant in Austin who has criticized Texas’ response to the blackouts as insufficient.

Airlines canceled more than 1,000 flights in the U.S. scheduled for Wednesday, the flight-tracking service FlightAware.com showed, including more than half taken off the board in St. Louis. In an effort to stay ahead of the weather, Southwest Airlines announced Tuesday that it would suspend all of its flight operations Wednesday at St. Louis Lambert International Airport and Thursday at its Dallas Love Field hub.

“Around the country, we’re planning to operate a limited or reduced schedule from some cities in the path of the storm but will make adjustments to the schedule as needed,” Southwest spokesman Dan Landson said.

Missouri Gov. Mike Parson declared a state of emergency as school districts and universities shifted classes to online or canceled them entirely.

Chicago O’Hare International Airport also canceled more than 100 departing flights, and airports in Kansas City and Detroit were also canceling more flights than usual.

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 (15 to 30 centimeters) 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. That includes Detroit, where the mayor activated snow emergency routes and city crews were expected to work 12-hour shifts salting and plowing major roads.

In Oklahoma, Gov. Kevin Stitt has declared a statewide state of emergency as the winter storm approaches. That suspends requirements for size and weights permits of oversized vehicles transporting materials and supplies used for emergency relief and power restoration. The declaration would remain in effect for seven days.

In Tulsa, Oklahoma, where up to 7 inches (18 centimeters) 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.