Almost 12,000 flights across the U.S. set to take off over the weekend were canceled as a monster storm started to wreak havoc Saturday across much of the country and threatened to knock out power for days and snarl major roadways with dangerous ice.

Roughly 140 million people, or more than 40% of the U.S. population, were under a winter storm warning from New Mexico to New England. The National Weather Service forecast warned of widespread heavy snow and a band of catastrophic ice stretching from east Texas to North Carolina. By midday Saturday, a quarter of an inch (0.6 centimeters) of ice was reported in parts of southeastern Oklahoma, eastern Texas and portions of Louisiana.

"What really makes this storm unique is, just following this storm, it's just going to get so cold," said Allison Santorelli, a meteorologist with the National Weather Service. "The snow and the ice will be very, very slow to melt and won't be going away anytime soon, and that's going to hinder any recovery efforts."

Governors in more than a dozen states sounded the alarm about the turbulent weather ahead, declaring emergencies or urging people to stay home.

"Please use these final hours to be prepared, to make sure that you have blankets and warmth and food to make it through this storm," Virginia Gov. Abigail Spanberger said Saturday at a news conference. "And every Virginian should stay off the road as of this evening, all day Sunday, and at least into the morning on Monday."

Snow covered mostl -empty highways in the suburbs north of Dallas. Ice and sleet that hit northern Texas overnight moved toward the central part of the state on Saturday. By mid-morning Saturday, ice had formed on roads and bridges in a third of Mississippi's counties.

Little Rock, Arkansas, was covered with sleet and snow Saturday morning, giving Chris Plank doubts about whether he would be able to make a five-hour drive to Dallas for work on Sunday. While some snow was a yearly event, he could only recall three ice storms in the previous 20 years that he had lived in Little Rock, and that potential ice concerned him the most.

"All of the power lines are above ground, so it doesn't take very much to end up in the dark," Plank said Saturday morning.

Forecasters say the damage, especially in areas pounded by ice, could rival that of a hurricane.

Around 120,000 power outages were reported in the path of the winter storm Saturday afternoon, including about 56,000 in Texas, 36,000 in Louisiana and nearly 10,000 in New Mexico, according to poweroutage.us.

In Shelby County, Texas, near the Louisiana border, ice weighed down on pine trees and caused branches to snap, downing power lines. About a third of the county's 16,000 residents were without power on Saturday.

"We have hundreds of trees down and a lot of limbs in the road," Shelby County Commissioner Stevie Smith said from his pickup truck. "I've got my crew out clearing roads as fast as we can. It's a lot to deal with right now."

All Saturday flights were canceled at Will Rogers International Airport in Oklahoma City, and all Sunday morning flights also were called off, as officials aimed to restart service Sunday afternoon at Oklahoma's biggest airport.

As of 1 p.m. ET, more than 3,700 flights were canceled Saturday across the country, according to the flight tracking website FlightAware. Almost 8,000 flights were called off for Sunday. Among the hardest hit airports were Dallas-Fort Worth International Airport, Nashville International Airport and Charlotte Douglas International Airport.

After sweeping through the South, the storm was expected to move into the Northeast, dumping about 1 to 2 feet (30 to 60 centimeters) of snow from Washington through New York and Boston, the weather service predicted.

"Please, if you can avoid it, do not drive, do not travel, do not do anything that can potentially place you or your loved ones in danger," New York City Mayor Zohran Mamdani said Saturday. "Instead, I urge every New Yorker who can to put a warm sweater on, turn on the TV, watch ‘Mission Impossible' for the 10th time, above all to stay inside."

Officials in Georgia advised people in the state's northern regions to get off the roads by sundown Saturday and be prepared to stay put for at least 48 hours.

Will Lanxton, the senior state meteorologist, said Georgia could get "perhaps the biggest ice storm we have expected in more than a decade" followed by unusually cold temperatures.

"Ice is a whole different ballgame than snow," Lanxton said. "Ice, you can't do anything with. You can't drive on it. It's much more likely to bring down power lines and trees."

Crews began treating highways with brine after midnight Saturday, with 1,800 workers on 12-hour shifts, Georgia Department of Transportation Commissioner Russell McMurry said.

"We're going to do what we can to keep the ice from sticking to the roads," McMurry said. "This is going to be a challenge."

The Midwest saw windchills as low as minus 40 F (minus 40 C), meaning that frostbite could set in within 10 minutes. The minus 36 F (minus 38 C) reading in Rhinelander, Wisconsin, on Saturday morning was the coldest in almost 30 years.

In Minneapolis, the worst of an extreme cold wave was over, but protesters calling for ICE to leave Minnesota on Saturday still faced an outdoor temperature of minus 6 degrees Fahrenheit (minus 21 Celsius).

Workers from The Orange Tent Project, a Chicago nonprofit that provides cold weather tents and other supplies to unhoused individuals throughout the city, went out to check on those who did not or could not seek shelter.

"Seeing the forecasted weather, I knew we had to come out and do this today," said CEO Morgan McLuckie.

Churches moved Sunday services online, and the Grand Ole Opry in Nashville, Tennessee, decided to hold its Saturday night radio performance without fans. Mardi Gras parades in Louisiana were canceled or rescheduled.

Schools superintendents in Philadelphia and Houston announced that schools would be closed Monday.

Some universities in the South canceled classes for Monday, including the University of North Carolina at Chapel Hill and the University of Mississippi's main campus in Oxford.

Around the southeast, people used the cancellations to have some fun. On a hill outside the Capitol building in Nashville, adult sledders on green discs and inflatable pool animals giggled with joy as they slid in the snow.

President Donald Trump said via social media on Friday that his administration was coordinating with state and local officials, and "FEMA is fully prepared to respond."

Nine states have requested emergency declarations, according to a FEMA briefing document released Saturday. The declarations can unlock federal emergency resources. Trump on Friday approved emergency declarations for South Carolina and Virginia, and requests from Arkansas, Kentucky, Louisiana, Maryland, North Carolina, Tennessee and West Virginia were still pending as of Saturday morning.

"I think there are two parts of this storm that make it unique. One is just a broad expanse of spatial coverage of this event ... You've got 2,000 miles of country that's being impacted by the storm with snow, sleet, and freezing rain," said Josh Weiss, a meteorologist at NOAA's Weather Prediction Center. "The other part of this storm that's really impressive is what's going to happen right afterward. We're looking at extreme cold, record cold."