The United States is being gripped by record-breaking cold and snow as forecasters warn of life-threatening conditions and wind chill as low as 60 degrees below zero.
Icy conditions caused havoc across the midwest and thousands of flights were cancelled or delayed, days after the northeast was hammered by the first winter storm of the season.
“The coldest temperatures in almost two decades will spread into the northern and central US today behind an Arctic cold front,” the National Weather Service said on Sunday.
“Combined with gusty winds, these temperatures will result in life-threatening wind chill values as low as 60 degrees below zero.”
In weather that cold, frostbite can set in on uncovered skin in a matter of minutes, experts warned.
Minnesota Governor Mark Dayton ordered all public schools in the state to be closed on Monday to protect children from dangerously cold weather.
Chicago public schools followed suit – reversing an earlier decision – saying in a statement on their website that it would be dangerous for children to commute to school amid sub-zero temperatures and high winds.
The NWS said the widespread chill was a result of a relatively infrequent alignment of weather conditions, allowing the Arctic polar vortex to be displaced unusually far south.
Forecasters warned Chicago and Indianapolis could see overnight lows of minus 12F (-24C), Minneapolis minus 29F (-34C) and Fargo, North Dakota, minus 31F (-31C).
The coldest temperature reported in the lower 48 states on Sunday was minus 40F (-40C) in the towns of Babbitt and Embarrass, Minnesota, according to the National Weather Service.
Between 6 inches and a foot (15-30cm) of snow was predicted from Chicago to Detroit, AccuWeather said, while icy sleet and rain was forecast for much of the northeast, where a brief thaw was forecast before intense cold returned late Monday.
Officials closed several Illinois roads because of drifting snow, and warned residents to stay inside.
Roads in the midwest were particularly dangerous, and officials in Missouri warned it was too cold for rock salt to be very effective.
Authorities also urged residents to check on elderly and disabled relatives and neighbours.
The deep freeze extended into Canada where parts of eastern Alberta and northwest Ontario were under wind chill warnings.
What is a polar vortex
The polar vortex is the pattern of winds around the North Pole. They occur seasonally and their formation resembles that of hurricanes in more tropical regions: fast-moving winds build up around a calm center. Unlike a hurricane, these are frigid polar winds, circling the Arctic at more than 100 miles per hour. The spinning winds typically trap this cold air in the Arctic. But the problem comes when the polar vortex weakens or splits apart, essentially flinging these cold wind patterns out of the Arctic and into our backyards.
Despite the dangerous cold, in Wisconsin fans of the American football team Green Bay Packers made their way to Lambeau Field for Sunday’s NFL (National Football League) playoff game against the San Francisco 49ers.
It was among the coldest ever played: it was five degrees fahrenheit (minus 15 celsius) at kickoff.
One fan said she was wearing “four layers of long johns (thermal underwear), two sets of snow pants, four shirts, a sweatshirt, and a coat”.
It has not been this cold for almost two decades in many parts of the US.
Frostbite and hypothermia can set in quickly at 15 to 30 below zero fahrenheit (26 to 34.4 below zero celsius).
Travel problems started early on Sunday. In New York City, a plane from Toronto landed at John Fitzgerald Kennedy International Airport and then slid into snow on a taxiway.
No one was hurt, though the airport temporarily suspended operations because of icy runways.
This came a day after a small plane travelling to Connecticut after a tour of the Statue of Liberty made an emergency landing on the Major Deegan Expressway in the Bronx, New York City.
Neither the pilot nor his two passengers were seriously injured.
About 1,300 flights had been cancelled Sunday at O’Hare and Midway international airports in Chicago, aviation officials said, and there also were cancellations at Logan International Airport in Boston and Tennessee’s Memphis and Nashville international airports.
Snow and ice were blamed for a multi-vehicle pileup in Staten Island, New York City, on Sunday morning.
At least a dozen vehicles were involved in the pileup along an icy stretch of the Staten Island Expressway.