DETROIT - A dangerously frigid arctic air mass gripped a vast expanse of the United States on Thursday, ahead of what could be one of the coldest Christmas Days on record, as a looming winter storm threatens to upend travel plans for millions of Americans.

Leading into the holiday weekend, the impending storm is expected to bring blizzard conditions to the Great Lakes region, up to 5cm of rain followed by a flash freeze on the East Coast, wind gusts of 100kmh and bitter cold as far south as the Mexican border.

As the storm took shape over the Great Lakes on Thursday, a weather phenomenon known as a bomb cyclone was expected to develop from a “rapidly deepening low-pressure” system, the National Weather Service (NWS) said.

The cyclone could spawn snowfalls of 1.25cm per hour and howling winds gusting to 97kmh from the Upper Midwest to the interior North-east, producing blizzard conditions and near-zero visibility, the weather service said.

Combined with the arctic cold, wind-chill factors as low as -40 deg C are forecast in the High Plains, the northern Rockies and Great Basin, the NWS said. Exposure to such conditions without adequate protection can cause frostbite within minutes.

Power outages are likely, and the storm is expected to make travel by land or air precarious or impossible at times.

The extreme cold posed a particular hazard to livestock in the ranching-intensive region. Tyson Foods, the nation’s leading meat producer by sales, said it had scaled back operations to protect employees and animals.

“It’s dangerous and threatening,” President Joe Biden said at the White House, urging Americans with travel plans to not delay and to set off on Thursday. “This is not like a snow day, when you were a kid; this is serious stuff.”

By afternoon, well over half of the lower 48 states, from Washington state to Florida, were under wind-chill alerts and other winter weather advisories affecting more than 200 million people, or roughly 60 per cent of the US population, the weather service reported. 

The NWS map of looming weather hazards on Thursday, stretching from border to border and coast to coast, “depicts one of the greatest extends of winter weather warnings and advisories ever”, the agency said. 

‘White-out’ Christmas

The storm front could bring more than 30cm of snow to some areas as it moves eastward out of the Plains and Great Lakes, weather service meteorologist Ashton Cook said. Snow squalls – brief bursts of moderate to heavy snow and strong wind – are expected from Illinois to Indiana, and could produce white-out conditions.

The American Automobile Association (AAA) estimates 112.7 million people plan to travel 80km or more from home between Dec 23 and Jan 2, up 3.6 million travellers over last year and closing in on pre-pandemic numbers.

More than 4,500 US flights scheduled for Thursday and Friday have been cancelled, with two major airports in Chicago accounting for more than 1,200 of the cancellations, according to flight-tracking service FlightAware.

“They’re ruining Christmas,” Ms Nadia Dickens, 42, a management company worker in Gallatin, Tennessee, said on Thursday after her flight from Nashville was cancelled.

She was headed for Corpus Christi, Texas, for a Christmas Day family gathering, where she was looking forward to making tamales with her 94-year-old grandmother.

Ms Dickens managed to book another flight to Austin, Texas, after a relative offered to make the four-hour drive to get her to the family reunion, but she remained pessimistic.

“We’re going to get an inch of snow overnight and the weather is just dreadful all over the place,” she said.

The frigid air mass that had already enveloped northern states is pushing south through central Oklahoma and north-western Texas, where the mercury plunged to single digits on Thursday.

Hundreds of Texans died in February 2021 after the state’s power grid failed amid wintry storms, leaving millions without electricity. The Electric Reliability Council of Texas (Ercot), which has since worked to safeguard its grid, “expects sufficient generation to meet forecasted demand at this time”, spokesman Christy Penders said. 

Temperatures in the Southern Plains and South-east could stay below freezing – but still 30-plus degrees less than normal – for multiple days, the NWS predicted.

Mr Greg Carbin, chief of forecast operations at the Weather Prediction Centre in Maryland, said freezing or below-freezing cold is expected to bisect Florida from Pensacola through Orlando to Daytona Beach, with temperatures about 25 degrees below normal.

Motorists in the Ohio and Tennessee valleys were warned that wet roads could instantly freeze over due to a rapid drop in temperatures.

The weather service also warned of freezing rain in parts of Oregon and Washington in the North-west, where a separate storm was forming on Thursday.

Georgia on Wednesday joined North Carolina and Kentucky in declaring states of emergency. Temperatures in north Georgia were forecast to hit -12 deg C with subzero wind chills.

“We are expecting weather we haven’t seen in a decade or more,” Georgia Governor Brian Kemp said at a media briefing.

Mr Brandon Mattis, 24, said his flight from New York City to Atlanta was cancelled on Thursday morning because of the coming storm, leaving him “flustered” at LaGuardia Airport in Queens. “There was no rescheduling or anything like that,” he said.

Mr Mattis said he searched for alternate routes and was even considering a 21-hour bus ride to Atlanta. “Anything we can do just to get there, we’re going to do,” he said. REUTERS