The Arctic front forced schools to shut down in parts of the United States, while authorities warned people to not to stay out too long to avoid hypothermia and urged pet owners to keep their animals indoors.

The crushing cold has claimed at least three lives since Monday.

Two people were found dead -- one on a street, the other in a home -- in Illinois' Cook County "in the last couple of days," a spokeswoman for the medical examiner's office said Tuesday. She had no further details.

An 81-year-old woman was found dead in a ravine near her home in a Washington suburb, The Washington Post reported.

Schools closed Tuesday in parts of the state of Wisconsin, where temperatures slid to as low as minus 24 degrees Celsius (minus 11 Fahrenheit) on Monday.

In Canada, a wind-driven chill dropped temperatures to as low as minus 45 C (minus 49 F) in the central city of Winnipeg. No cold-related deaths were reported in Canada.

"Everybody (was asking) where was winter," said David Phillips, a senior climatologists at the Canada's environment ministry. "Here we are, the second coldest country in the world, and there were people assuming that we were going to lose our reputation."

"We had no blizzards, no windchills to sneer at or frostbites that were causing people to go to an emergency room," he said. "It was really almost as if the winter had been canceled."

The Arctic air has filled the central and eastern half of North America, with temperatures eight to 10 C colder than normal driven by windchill that threaten to freeze flesh in less than 10 minutes in some places, Phillips said.

"There was that general feeling there that ... this (was) global warming and we kept saying, 'no, no, it's just been postponed,'" he said.

"So it's almost there is a certain irony to it, though, just as people were talking about global warming, it's almost as if nature had the last laugh," he said. "The thing is with cold air, it's like a bully, it doesn't leave. It leaves only when it wants to leave and it fill every nook and cranny."

Dennis Feltgen, a meteorologist at the US National Weather Service, said the mild start to the winter season was caused by a "moderate strength" El Nino weather pattern.

El Nino is an occasional seasonal warming of the central and eastern Pacific Ocean that upsets normal weather patterns from the western seaboard of Latin America to East Africa, and potentially has a global impact on climate.

It was the fourth warmest winter on record in the United States, with temperatures 20 to 30 F above normal on the east coast in the first week of January, Feltgen said.

But El Nino has weakened in the last couple of weeks, bringing back a "more typical weather pattern," he said.

No record low temperatures have been recorded in the United States, he said.

"The temperatures have been running 20 degrees (F) below normal but it has been colder than this," he told AFP.

The sudden winter comeback might have surprised people following the unusually mild weather, Feltgen said.

"It doesn't have anything to do with global warming," he said. "The fact that it has been so mild and it is (now) the coldest mass ... I guess that people had forgotten what winter was all about."

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