Many states have been under weather alerts ahead of what could possibly be the coldest Christmas days on record.

Over 1,800 flights have been cancelled, and about 3,700 others have been delayed amid the winter storm.
Over 1,800 flights have been cancelled, and about 3,700 others have been delayed amid the winter storm. (AFP)

A massive winter storm system enveloped a vast stretch of the United States, threatening to upend the travel plans of millions of Americans ahead of what could turn out to be one of the coldest Christmas days on record in many cities.

Leading into the holiday weekend, the system is expected to bring blizzard conditions to the Great Lakes region, up to 2 inches of rain followed by a flash freeze on the East Coast, wind gusts of 100 kilometres per hour and bitter cold as far south as the Mexican border.

As the storm moves over the Great Lakes, a weather phenomenon known as a bomb cyclone is expected to develop due to "the abrupt deepening of this low-pressure system," the National Weather Service said. In its wake, the cyclone could spawn snowfalls of a half inch an hour and winds of more than 80 kph in the Upper Midwest and interior Northeast, the weather service said.

"This will lead to dangerous, to at times impossible, land and air travel leading up to the holiday weekend," the agency said on its website. Tree damage and power outages seemed likely as well, it said.

More than half of the Lower 48 states, from Washington state to Florida, are under winter weather alerts, including wind chill advisories affecting about 135 million people, said Ashton Robinson Cook, a meteorologist at the weather service's Weather Prediction Center.

Nearly 2,000 flights cancelled

Travel conditions, already bad in the Great Plains region, will gradually deteriorate in the Midwest and Great Lakes area as the cold front moves east and brings more than a foot of snow with it to some parts, he said.

More than 1,800 flights have been cancelled in the morning, and at least five US states -- Kentucky, Missouri, Oklahoma, Georgia and North Carolina -- have already implemented emergency plans, and others were likely to follow.

"This is not like a snow day when you were a kid," President Joe Biden told reporters at a White House briefing on the weather and transport turmoil.

"This is serious stuff," he added, urging people to heed warnings from local authorities.

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

Many US airlines have waived change fees and fare differences for passengers.

The frigid air mass that had already enveloped northern states was pushing south through central Oklahoma and northwestern Texas, where the mercury is expected to plunge to about -7 Celsius degrees on Thursday. Combined with wind gusts of up to 100 kph, wind chills could go as low as minus 40 C.

Temperatures in parts of the Southern Plains and Southeast could stay below freezing -- 30-plus degrees less than normal -- for multiple days, the weather service predicted.

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Source: TRTWorld and agencies