Seventeen states and the District of Columbia have declared weather emergencies, the Department of Homeland Security said.

Jan 26 (Reuters) - Tens of millions of Americans were digging out on a bitterly cold Monday in the aftermath of a monster winter storm that dumped a foot of snow from New Mexico to New England, paralyzed much of the eastern United States, scuttled thousands of flights and caused widespread power outages.

From New York and Massachusetts in the northeast to Texas and North Carolina in the south, roads were frozen slick with ice and buried under often more than a foot of snow. In some southern states, residents faced winter conditions unseen for decades, with inch-thick ice bringing down trees and power lines.

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While the storm system was expected to drift away from the East Coast into the Atlantic on Monday, a blast of Arctic air was rushing in from Canada behind it, prolonging sub-freezing temperatures for several more days, the National Weather Service said.

"This storm is exiting the East Coast now, with some lingering snow squalls," said Allison Santorelli, a meteorologist with the NWS's Weather Prediction Center. "But the big picture story is the extreme cold, it's lasting into early February."

Almost 200 million Americans are under some form of extreme cold alert, from along the Canadian border to the Gulf of Mexico, forecasters said. Lubbock, Texas, had a low of minus 4 degrees Fahrenheit (-20 degrees Celsius) on Monday, and New York City, Washington D.C. and Boston all faced single-digit temperatures through much of the week ahead.

More than 800,000 homes and businesses across the southeastern U.S. were facing the cold weather without power, according to the tracking site PowerOutage.us, including more than a quarter million customers in Tennessee.

The storm snarled air traffic, with more than 12,500 U.S. flights canceled on Sunday - the most of any day since the onset of the COVID-19 pandemic in 2020.

About 3,900 flights within, into or out of the United States had already been canceled on Monday as of 9:15 a.m. ET (1415 GMT), according to the tracking website FlightAware. U.S. Transportation Secretary Sean Duffy told CNBC he hopes airports will be "back to normal" by Wednesday.