MISSION, Kan. (AP) — Travelers across much of the eastern United States were bracing Thursday for one of the most treacherous Christmas weekends in decades, with forecasters warning of a “bomb cyclone” that will pack heavy snow and wind while sending temperatures plummeting 50 degrees Fahrenheit in a matter of hours.

The frigid air was moving through the central United States to the east, with windchill advisories affecting about 135 million people over the coming days, weather service meteorologist Ashton Robinson Cook said Thursday. Places like Des Moines, Iowa, will feel like minus 37 degrees, making it possible to suffer frostbite in less than five minutes.

There were already widespread disruptions in flights and train travel.

“This is not like a snow day when you were a kid,” President Joe Biden warned Thursday in the Oval Office after a briefing from federal officials. “This is serious stuff.”

Forecasters are expecting a bomb cyclone — when atmospheric pressure drops very quickly in a strong storm — to develop near the Great Lakes, which will increase winds and create blizzard conditions, Cook said.

In South Dakota, Rosebud Sioux Tribe emergency manager Robert Oliver said tribal authorities have been working to clear roads to deliver propane and fire wood to homes, but face a relentless wind that has created drifts over 10 feet in some places.

“This weather and the amount of equipment we have — we don’t have enough,” Oliver said, noting that rescues of people stranded in their homes had to be halted early Thursday when the hydraulic fluid in heavy equipment froze amid a 41 below zero windchill.

He said five have died in recent storms, including a blizzard from last week. Oliver offered no details, saying the families are mourning.

“It’s just kind of scary for us here, we just kind of feel isolated and left out,” said Shawn Bordeaux, a Democratic state lawmaker, who said he was running out of propane heat at his home near Mission on the tribe’s reservation.

In Texas, temperatures were expected to quickly plummet Thursday, but state leaders promised there wouldn’t be a repeat of the February 2021 storm that overwhelmed the state’s power grid and was blamed for hundreds of deaths.

“I think trust will be earned over the next few days as people see that we have ultra-cold temperatures and the grid is going to be able to perform with ease,” Gov. Greg Abbott said in a news conference Wednesday.

The cold weather extended to El Paso and across the border into Ciudad Juarez, Mexico, where migrants have been camping outside or filling shelters as they await a decision on whether the U.S. will lift restrictions that have prevented many from seeking asylum.

Elsewhere in the U.S., authorities worried about the potential for power failures and warned people to take precautions to protect older and homeless people and livestock — and, if possible, to postpone travel. Some utilities were urging customers to turn down theirs thermostats to conserve energy.

“This event could be life-threatening if you are stranded,” according to an online post by the National Weather Service in Minnesota, where transportation and patrol officials reported dozens of crashes and vehicles off the road.

Michigan State Police prepared to deploy additional troopers to help motorists. And along Interstate 90 in northern Indiana, crews were braced to clear as much as a foot of snow as meteorologists warned of blizzard conditions there starting Thursday evening.

More than 1,846 flights within, into or out of the U.S. had been canceled as of midday Thursday, according to the tracking site FlightAware. Airlines have also canceled 931 Friday flights. Chicago’s O’Hare and Midway airports and Denver’s airport were reporting the most cancelations.

Among those with canceled flights was Ashley Sherrod, who planned to fly from Nashville to Flint, Michigan, on Thursday afternoon. Sherrod is now debating whether to drive or risk booking a Saturday flight she worries will be canceled.

“My family is calling, they want me home for Christmas, but they want me to be safe too,” said Sherrod, whose bag — including the Grinch pajamas she was planning to wear to a family party — is packed and ready by the door. “Christmas is starting to, for lack of a better word, suck.”

Amtrak, meanwhile, canceled service on more than 20 routes, primarily in the Midwest. Service between Chicago and Milwaukee, Chicago and Detroit, and St. Louis and Kansas City, Missouri, was suspended through Christmas Day.

Some shelters in the Detroit area already were at capacity, including all 140 beds at COTS, a family-only shelter. The facility is hoping to make room for others, though, spokesperson Aisha Morrell-Ferguson told The Detroit News.

“We are not sending anyone back into this cold,” Morrell-Ferguson said.

And in Portland, officials opened four emergency shelters after declaring a state of emergency because of severe cold.

In Montana, temperatures fell as low as 50 below zero (minus 46 Celsius) at Elk Park, a mountain pass on the Continental Divide. Schools and several ski areas announced closures, and several thousand people lost power.

Near Big Sandy, Montana, rancher Rich Roth said he wasn’t too concerned about his 3,500 pregnant cows weathering the cold snap, saying “they’re pretty dang resilient animals” and are acclimated to the weather.

In famously snowy Buffalo, New York, forecasters predicted a “once-in-a-generation storm” because of heavy lake-effect snow, wind gusts as high as 65 mph (105 kph), whiteouts and the potential for extensive power outages. Mayor Byron Brown urged people to stay home, and the NHL postponed the Buffalo Sabres’ home game against the Tampa Bay Lightning.

Denver, also no stranger to winter storms, was the coldest it has been in 32 years on Thursday, when the temperature dropped to minus 24 (minus 31 Celsius) in the morning at the airport.

In Charleston, South Carolina, a coastal flood warning was in effect Thursday. The area, a popular tourist destination for its mild winters, braced for strong winds and freezing temperatures.

The wintry weather extended into Canada, causing delays and cancellations earlier in the week at Vancouver International Airport. A major winter storm was expected Friday into Saturday in Toronto, where wind gusts as high as 60 mph (100 kph) were predicted to cause blowing snow and limited visibility, Environment Canada said.