A powerful winter storm is expected to blanket much of the US with heavy snow and life-threatening wind chills.
The storm is set to hit the country on Wednesday, likely sparking holiday travel chaos for millions of Americans.
About 200 million people are under extreme weather alerts as cold air descends from the Northern Plains, causing temperatures to nosedive, said Bob Oravec, a forecaster with the National Weather Service.
He said “rapid temperature drops, sometimes 50 or more degrees (Fahrenheit) colder than the previous day,” were likely, adding “it’s a pretty powerful, powerful system”.
The storm, fed by moisture from the Great Lakes, could dump up to a foot of snow on the Upper Midwest between Wednesday and Friday, with blizzard conditions stretching from the Northern Plains states to the Great Lakes region.
By Thursday night, a so-called “bomb cyclone” will likely form along the strong Arctic front across the Great Lakes, sending pressure sharply lower in a 24-hour period, potentially driving temperatures to record-breaking lows on the Gulf Coast and in Florida and the eastern US by Friday, Oravec said.
Heavy rainfall, strong winds and potentially dangerous coastal flooding are in store for parts of the northeast coastline and New England on Thursday and Friday, the weather service said, before the Arctic front arrives and causes a freeze. As much as 7.6cm of rain is predicted.
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Officials are warning of severe travel disruption due to the weather. With temperatures dropping more than 11C (20F) within hours, wet roads could suddenly turn to ice, the weather service warned.
“We had a great Thanksgiving week with minimal disruption. Unfortunately, it’s not going to be that way going into Christmas,” US transportation secretary Pete Buttigieg told MSNBC.
Americans traveling by air should prepare for delays and be flexible in their plans, while drivers also need to be prepared for severe weather, he added.
Southwest Airlines said it has cancelled 500 of its 4,000 scheduled flights on Thursday and Friday. The company said it wanted to maintain safe operations for both passengers and crew.
At least 145 flights into or out of Denver International Airport were cancelled Wednesday as the city was hit with snow, gusty winds and freezing temperatures, according to FlightAware, a flight tracking company. At least 219 flights into or out of Denver were expected to be cancelled Thursday.
FlightAware was also expecting at least 364 flights to be cancelled Thursday at O’Hare and Midway airports in Chicago. Earlier this week, those two airports said they had 350 pieces of snow removal equipment and 400,000 gallons of pavement de-icing fluid on hand for the storm.
Delta, American, United, Frontier, Alaska, Southwest and other airlines were waiving change fees and offering travellers the option of choosing new flights to avoid the bad weather.