Double dose of nasty winter about to smack much of US with snow, ice, biting cold

As the storm moves out on Monday, hundreds of millions of people in the eastern two-thirds of the nation will be plunged into dangerous bone-chilling air and wind chills all week, government and private forecasters said. Temperatures could be 12 to 25 degrees Fahrenheit (7 to 14 degrees Celsius) colder than normal as the dreaded polar vortex stretches down from the high Arctic bringing chilly weather, they said.

“This could lead to the coldest January for the US since 2011," AccuWeather Director of Forecast Operations Dan DePodwin said on Friday.

“It's not just one day of this. It's going to be three to five, in some cases a week or more of temperatures that are well below historical average.” The biggest drop below normal is likely to be centred over the Ohio Valley, but significant unusual cold will extend southward all the way to the Gulf Coast, said Danny Barandiaran, a meteorologist at the National Weather Service's Climate Prediction Centre.

Forecasts have moderated a bit from last week when some computer models envisioned the worst cold spell in decades. Now it's unlikely many cold records will break, but it will still have a big impact on the country, Barandiaran said.

There should even be a hard freeze in Florida, while areas near the Canadian border will be around zero, Barandiaran said.

“It's not going to thaw out for awhile,” Maue said.

Woodwell Climate Research Institute climate scientist Jennifer Francis said the initial blasting winds from the north may shock people after a fairly warm last couple of years.

“The wind chills are going to be brutal,” she said. "There'll be a lot of whining, but it is winter. ... Just because the globe is warming doesn't mean these cold snaps are going away.” This double dose of nasty weather may be triggered in part by a fast-warming Arctic, serving as a not-so-gentle reminder that climate change gooses weather extremes, even winter ones, said Francis and Judah Cohen, seasonal forecast director at the private firm Atmospheric and Environmental Research.

The polar vortex, ultra-cold air spinning like a top 15 to 30 miles high, usually stays penned up above the North Pole. But sometimes it escapes or stretches down to the United States, Europe or Asia. And that's when large numbers of people get intense doses of cold.

Cohen and colleagues have published several studies showing an increase in the polar vortex stretching or wandering. Cohen, Francis and others last month published a study that attributed these cold outbreaks partly to changes from an Arctic that's warming four times faster than the rest of the globe.

The change in temperature and loss of Arctic sea ice make the jet stream — the river of air that moves storm fronts — wavier, allowing plunges of cold air to come south and extreme weather to stay put, Francis said.

What's about to hit “is a really good example of these kinds of cases,” Francis said.