NEW YORK: On Friday,  Bone-chilling cold that paralysed a large part of the United States this week and caused at least 18 deaths eased as an errant Arctic air mass retreated, setting the stage for 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) earlier this week, temperatures of 22F (minus 5.5C) on Friday afternoon felt positively balmy for some in the nation's third-largest city.

One commuter heading home from Chicago's downtown financial district said that "It's got to be an almost 50 degree difference, it feels like spring wearing only a sweatshirt to keep warm.” 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.

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Meteorologists linked the spell of brutal cold to 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 U.S. Midwest this week. Bryan Jackson, a National Weather Service meteorologist, said on Friday the core of the vortex was pulling back, though residual icy air was still pushing over to the U.S. Northeast.

Since Saturday,  At least 18 deaths in several states were linked to the deep freeze, and the number was expected to climb as authorities identified more victims.

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