Potential bomb cyclone is ‘serious stuff’, Biden warns as Arctic blast looms

US forecasters warned on Thursday of "potentially crippling impacts across central and eastern" parts of the country, producing widespread disruption to travel and utilities over the holiday season, as an arctic blast surged from west to east.

At the White House, after a briefing on the potential "bomb cyclone", Joe Biden said: "This is not like a snow day when you were a kid. This is serious stuff."

A bomb cyclone forms when atmospheric pressure drops very quickly in a strong storm. Forecasters expected that to occur near the Great Lakes, increasing winds and creating blizzard conditions.

About 200 million people in the lower 48 states were under extreme weather alerts, said Bob Oravec, a forecaster with the National Weather Service (NWS) in College Park, Maryland.

An NWS advisory said the "powerful winter storm" would "produce widespread disruptive and potentially crippling impacts across the central and eastern United States".

"Record-breaking cold and life-threatening wind chills" were forecast "over the Great Plains to overspread the eastern half of the nation by Friday", with "significant freezing rain possible across parts of western Oregon and Washington" state from Thursday night.

In Portland, Oregon, the mayor, Ted Wheeler, declared a state of emergency. So did Multnomah county, home to Portland.

Chris Voss, director of emergency management in Multnomah county, said his biggest worry was a precipitous drop in temperature expected in a region where lower than 25F (-4C) is uncommon. With wind chill, those living on the streets could experience temperatures that feel below zero, Voss said.

According to the NWS, the "major and anomalous storm system" was expected to produce "a multitude of weather hazards through early this weekend", including "heavy snowfall, strong winds and dangerously cold temperatures.

"At the forefront of the impressive weather pattern is a dangerous and record-breaking cold air mass in the wake of a strong Arctic cold front diving southward."

In some states temperatures had already begun to deteriorate quickly, plunging in Denver on Wednesday, the first official day of winter, from a daytime-high 51F (10C) into the low-single digits. Below zero was expected by Thursday.

"That's the kind of changes that are going to be occurring as this front pushes southward," Oravec told the AP. "Rapid temperature drops, sometimes 50 or more degrees colder than the previous day. It's a pretty powerful system."

The extreme weather coincided with the start of a holiday travel season shaping up as one of the busiest in decades, as travel bounces back from the Covid pandemic. Nearly 113 million people could travel more than 50 miles beginning on Friday, according to the American Automobile Association.

More than 1,700 flights scheduled between Wednesday and Friday, including services into and out of the US, were canceled, the flight-tracking service FlightAware said. Airlines including Delta, United Airlines and American Airlines waived change fees and fare differences for passengers in a range of affected areas.

Amtrak 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 was suspended through Christmas Day.

The US transportation secretary, Pete Buttigieg, told MSNBC: "We had a great Thanksgiving week with minimal disruption. Unfortunately, it's not going to be that way going into Christmas."

The storm could dump up to a foot of snow on the upper midwest between Wednesday and Friday, with blizzards from the northern Plains to the Great Lakes.

By Thursday night, Oravec added, a bomb cyclone will probably form, driving temperatures to record-breaking lows on the Gulf coast and the eastern US by Friday.

Wind-chill and hard-freeze warnings extended through much of Texas, Louisiana and Alabama, with a hard-freeze watch for the Florida panhandle. Freezing weather and wind chills cold enough to induce frostbite on exposed skin in minutes were widely expected.

Wind-chill values dropping to -40F were expected across the west, from the Cascades to the Rockies and into the plains, with some areas seeing wind chill as low as -70F, the NWS said, adding that the extreme cold posed a particular danger to livestock.

The storm will test new winterization measures on the Texas power grid. Hundreds died in February 2021 after storms overburdened the grid and millions lost power. Officials at the Electric Reliability Council of Texas said this week they were confident the grid could handle increased demand.

In a press conference on Thursday, the Republican governor, Greg Abbott, said he was also confident the state was now up to the challenge.

"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," he said.

Heavy rains, strong winds and coastal flooding were in store for parts of the north-east. The arctic front was expected thereafter, causing wet roads to freeze and ice to form on power lines.

North Carolina and Kentucky declared states of emergency while West Virginia issued a state of preparedness. Colorado activated 100 national guard troops.