"The cold snap will persist through Christmas," said meteorologist Ashton Robinson Cook, at the NWS Weather Prediction Center.

Minneapolis was the coldest spot in America on Saturday at minus-6 degrees Fahrenheit. On Christmas morning, the coldest spot will be Fargo, North Dakota at minus-20, Cook said.

It will start to moderate west-to-east across America, with the high plains and Central U.S. getting back to normal by Tuesday, but it won't warm up on the East Coast until Thursday or Friday, he said.

"For now it's staying cold," he said.

The severe weather prompted authorities across the country to open warming centers in libraries and police stations while scrambling to expand temporary shelter for the homeless. The challenge was compounded by an influx of migrants crossing the US southern border by the thousands in recent weeks.

The National Weather Service said its map of existing or impending meteorological hazards "depicts one of the greatest extents of winter weather warnings and advisories ever." 

Reuters