The ice and snowfall were expected to continue through Monday in much of the country, followed by very low temperatures, causing “dangerous travel and infrastructure impacts” to linger for several days, the National Weather Service said.

Heavy snow was forecast from the Ohio Valley to the Northeast, while “catastrophic ice accumulation” threatened from the Lower Mississippi Valley to the Mid-Atlantic and Southeast.

“It is a unique storm in the sense that it is so widespread,” weather service meteorologist Allison Santorelli said in a phone interview. “It was affecting areas all the way from New Mexico, Texas, all the way into New England, so we’re talking like a 2,000-mile spread.”

As of Sunday morning, about 213 million people were under some sort of winter weather warning, she said. The number of customers without power approached 840,000, according to poweroutage.us, and the number was rising.

Tennessee was hardest hit with more than 300,000 customers out, and Texas, Louisiana and Mississippi all had more than 100,000 customers in the dark.

More than 10,000 flights had already been canceled Sunday and another 8,000 have been delayed, according to the flight tracker flightaware.com. The biggest hubs hit so far were in Philadelphia, Washington, Raleigh-Durham in North Carolina, New York and New Jersey.

At Philadelphia International Airport, inside displays registered scores of canceled flights and few vehicles could be seen arriving Sunday morning.

Even once the ice and snow stop falling, the danger will continue, Santorelli warned.

“Behind the storm it’s just going to get bitterly cold across basically the entirety of the eastern two-thirds of the nation, east of the Rockies,” she said. That means the ice and snow won’t melt as fast, which could hinder some efforts to restore power and other infrastructure.

President Donald Trump had approved emergency declarations for at least a dozen states by Saturday, with more expected to come. The Federal Emergency Management Agency pre-positioned commodities, staff and search and rescue teams in numerous states, Homeland Security Secretary Kristi Noem said.

In New York City, Mayor Zohran Mamdani said at least five people died as temperatures plunged Saturday before the snows arrived in earnest.

“While it’s still too early to determine the causes of death, it is a reminder that every year New Yorkers succumb to the cold,” he wrote on X. “The danger of this weather cannot be overstated.”

The Democrat also announced that Monday would be a remote learning day for students in the nation’s largest school system.

Nashville and the surrounding area was seeing ice accumulations of half an inch or more, with icicles hanging from power lines and overburdened tree limbs crashing to the ground.

“We typically say that once you start seeing, you know, roughly a half an inch of ice, that’s when you’re going to start seeing the more widespread power outages,” Santorelli said.

In Oxford, Mississippi, police on Sunday morning used social media to tell residents to stay home as the danger of being outside was too great. Local utility crews were also pulled from their jobs during the overnight hours.

“Due to life-threatening conditions, Oxford Utilities has made the difficult decision to pull our crews off the road for the night,” the utility company posted on Facebook early Sunday.

“The situation is currently too dangerous to continue,” it said. “Trees are actively snapping and falling around our linemen while they are in the bucket trucks. We simply cannot clear the lines faster than the limbs are falling.”

Icy roads also made travel dangerous in north Georgia.

“You know it’s bad when Waffle House is closed!!!” the Cherokee County Sheriff’s office posted on Facebook with a photo of a shuttered restaurant. Whether the chain’s restaurants are open — known as the Waffle House Index — has become an informal way to gauge the severity of weather disasters across the South.

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Brumback reported from Atlanta. Walker reported from New York. Kristin Hall and Jonathan Mattise Nashville, Philip Marcelo in New York and Jeff Martin in Kennesaw, Georgia, contributed reporting.