More than 200 million people in nearly every US state are under various winter weather alerts, including for wind chill, ice and heavy snow, as a huge winter storm system threatens travel chaos and one of the coldest Christmas days on record.
The coast to coast alerts extend as far south as Florida, with blizzard conditions expected in the Great Lakes region, up to 2in (5cm) of rain and a flash freeze on the East Coast, and wind gusts of 60 miles (100 km) an hour on the Mexican border.
Thousands of homes have been left without power, and governors in at least 13 states have drawn up emergency response plans, including National Guard deployments, for the holiday weekend, with heavy snow and ice creating treacherous road conditions and some drivers stranded.
The National Weather Service (NWS) said it expected a weather phenomenon known as a bomb cyclone – a rapidly strengthening storm that drops 24 millibars of pressure within 24 hours – to develop as it moves into the Great Lakes on Friday.
The cyclone, with a pressure likely to match that of a category 2 hurricane, could bring snowfall of half an inch (1.3cm) an hour, the weather service said, leading to “dangerous, at times impossible, land and air travel” up to the holiday weekend.
“The ongoing major winter storm will continue to produce areas of heavy snow, strong winds, and life-threatening wind chills through Saturday. If traveling for the holiday, please use extreme caution and pay attention to the latest updates,” it said.
“This is not like a snow day, when you were a kid, this is serious stuff,” the president, Joe Biden, said on Thursday.
Temperatures in Colorado on Thursday dipped to a record-breaking low of -9F (-22.7C) from 42F (5.5C), while Cheyenne, Wyoming, recorded its greatest one-hour temperature drop, plunging from 43F to 3F in the space of 30 minutes.
The NWS said temperatures of -50F to -70F were possible over the weekend in some parts of the US, warning that even in big metropolitan areas such as Des Moines, Iowa, frostbite could become a significant danger.
Ahead of one of the busiest travel periods of the year, the American Automobile Association (AAA) said more than 112 million people planned to travel 50 miles (80 km) or more from home between 23 December and 2 January.
More than 2,000 US flights scheduled for Thursday and Friday have been cancelled, according to the flight-tracking service FlightAware, including more than 700 departures and arrivals at two major airports in Chicago and hundreds more in Denver.
The New York state governor Kathy Hochul declared an emergency, saying the threat of flooding and ice jams blocking rivers would “wreak a lot of havoc in our community”. The Ohio governor, Mike DeWine, called it “a unique and dangerous situation”.
In Georgia, where temperatures in the north were forecast to hit -12C, with subzero wind chills, the governor Brian Kemp said the state was “expecting weather we haven’t seen in a decade or more.”
More than half of the so-called 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 of the weather service’s prediction centre.
Travel conditions, already bad in the Great Plains region, are forecast to deteriorate in the midwest and Great Lakes area as the cold front moves east, with more than a foot of snow and whiteout conditions expected in some areas.
The NWS has described the storm as “once in a generation” weather event, saying more than 100 daily cold temperature records could be equalled or broken over the coming days. Florida is projected to experience its coldest Christmas in 30 years.
Friday is forecast to bring record low temperatures across swathes of the US, the NWS warned, accompanied by high winds likely to create dangerous wind chills across nearly all of the central to eastern US.
Temperatures in parts of the southern plains and south-east could stay below freezing – more than 30F less than normal – for several days, the weather service predicted, and also forecast freezing rain in parts of Oregon and Washington.