An Arctic air mass blamed for the deaths of more than 20 people in the U.S. began moving out to sea Friday, easing its grip on about a dozen states that have endured days of record-breaking cold.
"It's fairly rare to see this much of a turnaround in temperature in this sort of time", said Todd Kluber, a meteorologist with the National Weather Service.
It means a warmer weekend is forecast for the Midwest and the Northeast.
If you've been following the news at all, you probably already know what's to blame: the dreaded "polar vortex", which describes a large area of low pressure and cold air that surrounds both poles of the earth.
Temperatures on Friday afternoon ranged from the teens to the twenties, after cities like Chicago experienced sub-zero temperatures for two days and opened additional warming centres for the homeless.
"It feels like summer", said Dolores Marek (57) as she got off her commuter train in Chicago wearing a long parka coat and set out on the 2.4km walk to the local college where she works.
The term "Polar Vortex" has been widely used to describe the dangerously cold temperatures that have been plunging into the US from Canada.
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In Wisconsin, Governor Tony Evers has declared an emergency and requested help from the National Guard, according to the New York Times; In northern In, the University of Notre Dame said it would close its campus this evening through Thursday afternoon. "As it moves east, it'll bring in air from the south and we do expect it to warm up over the weekend".
Classes at the University of Iowa were cancelled on Thursday. "I'm not used to this".
The coldest recorded temperature was minus 56 in Cotton, Minnesota, on Thursday, the weather service said. The central Plains will be in around 14C to 16C, almost seven or eight degrees above normal, the weather service said.
It's led to eight deaths so far and that number is expected to rise.
United States media reported as many as 21 weather-related deaths since a snow storm hit the Midwest early last week, followed by plunging temperatures on Wednesday and Thursday. The death toll rose after at least nine more people in Chicago were reported to have died from cold-related injuries, according to Stathis Poulakidas, a doctor at the city's John H. Stroger Jr.
Amtrak train services that had been halted since Wednesday in Chicago's hub resumed yesterday, as did U.S. postal services that were halted or limited in six Midwest states.
More than 2,300 flights were cancelled across the USA on Thursday, according to the flight tracking website FlightAware.