The #FrozenPants Challenge, The Lighter Side To The Extreme Cold Snap

Americans are freezing in extreme cold weather, but frozen pants have littered front yards across the U.S., as people entertain themselves during the cold snap.

With temperatures dropping as low -30C due to an extreme polar vortex across much of the country, the 'Frozen Pants' challenge has become a social media hit.

To create the frozen spectacle, people are dipping their pants in water and then leaving them outside for the sub-zero temperature to do its thing.

Using the hashtag #frozenpants, people have shared their icy creations with the world.

One photo shows a postal delivery man standing with frozen jeans.

A video shows a child throwing their frozen pants in the air and watching as it lands upright and standing, still solid as ice.

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The bone-chilling cold that has paralysed a large swath of the United States and caused more than a dozen deaths is easing as an errant Arctic air mass retreats, setting the stage for a warmer weekend.

In Chicago, where the mercury dipped as low as 30 degrees below zero earlier this week, temperatures of -7C on Friday morning felt positively balmy for some in the nation's third-largest city.

Temperatures from southern New England to the Upper Midwest should reach 10C through the weekend and Monday, forecasters say, after a record-breaking cold snap that stopped mail deliveries in some parts of the Midwest and shuttered schools and businesses.

Steam rises from the city buildings and Lake Michigan in Chicago. Image: EPA

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 US Midwest this week.

National Weather Service meteorologist Bryan Jackson said on Friday the core of the vortex was pulling back, though residual icy air was still pushing over to the US Northeast.

Temperatures on Friday afternoon ranged from about -10C to -15C in most of the Midwest and Northeast, according to the weather service.

Mist rises from Chicago River in Chicago. Image EPA

More than a dozen deaths in several states were linked to the deep freeze since Saturday and the number was expected to climb as authorities identified more victims.

On Friday, police in East Moline, Illinois, 260 km west of Chicago, said the weather may have contributed to the death of a FedEx freight driver whose body was found between two trucks on Thursday outside a company distribution hub.

Cook County's medical examiner's office said there had been one confirmed cold-related death this week in the Chicago area.

Ice and snow builds up along Lake Michigan in Chicago. Image: EPA

A trauma surgeon at the city's largest public hospital had told Reuters news agency on Thursday there were nine cold-related deaths in the city.

Asked about the discrepancy, a spokeswoman for the hospital said they would defer to the medical examiner's office for a definitive tally.

More than 40 cold-temperature records were broken on Thursday, the coldest morning since the polar vortex moved in late on Tuesday.

The mass of Arctic air had clung to a swath of the United States from Iowa and the Dakotas across the Great Lakes region and into Maine for days.

With AAP.