Bone-chilling cold that paralyzed a chunk of the United States this week and killed at least 18 people eased  as an errant Arctic air mass retreated ahead of a warmer-than-normal weekend in areas of the Midwest and Northeast.

In Chicago, where the mercury dipped as low as minus 22 Fahrenheit (minus 30 Celsius) this week, temperatures of 22F (minus 5.5C) by Friday afternoon felt balmy for some in the nation’s third-largest city.

“It’s got to be an almost 50 degree difference, it feels like spring,” said one commuter heading home from Chicago’s downtown financial district, wearing only a sweatshirt.

“Today, working outside it was like normal,” said Stachovic, 40, wearing brown overalls and insulated gloves, as he worked in Chicago’s downtown.

Temperatures from southern New England to the upper Midwest should reach the mid-40s to low 50s Fahrenheit through the weekend and Monday, forecasters said, after a record-breaking cold snap that stopped mail deliveries in some parts of the Midwest and shuttered schools and businesses.

“The bitter cold air is going to be pushed up into Canada,” said Bob Smerbeck, senior meteorologist for Accuweather.

The Midwest’s worst cold snap in two decades was created by the polar vortex, a reservoir of icy air that usually swirls over the North Pole. Shifting air currents caused it to slip down through Canada and into the US Midwest this week.