A frigid winter storm has swept across the country, knocking out power to hundreds of thousands of homes and businesses and leaving millions of people on edge about the possibility of blackouts over the Christmas holiday weekend.

The storm unleashed its full fury on Buffalo, New York, with hurricane-force winds causing whiteout conditions. Emergency response efforts were paralyzed, and the city’s international airport was shut down.

CBS News has confirmed at least 20 weather-related deaths from the storm nationwide. At least three people died in the Buffalo area, including two who suffered medical emergencies in their homes and couldn’t be saved because emergency crews were unable to reach them amid historic blizzard conditions.

As millions of Americans were traveling ahead of Christmas, more than 3,400 flights within, into or out of the U.S. were canceled Saturday, and another 1,300 as of 7 a.m. ET Sunday, according to the tracking site FlightAware. Airlines were playing catch-up with crew shortages and de-icing slowing the return to normal, CBS News correspondent Naomi Ruchim reported. In Seattle, an ice storm shut down multiple runways.    

As of Saturday night, at least 345,000 customers were without power nationwide, according to the outage tracking site PowerOutage.us. Of those, more than 170,000 were in the New England region. 

Deep snow, single-digit temperatures and day-old power outages sent Buffalo residents scrambling Saturday to get out of their houses to anywhere that had heat. New York Gov. Kathy Hochul said the Buffalo Niagara International Airport would be closed through Monday morning and almost every fire truck in the city was stranded in the snow.

“No matter how many emergency vehicles we have, they cannot get through the conditions as we speak,” Hochul said.

Forecasters said 28 inches of snow had already accumulated as of Saturday in Buffalo — part of an area that saw 6 feet fall just over a month ago, resulting in three deaths. More is expected overnight.  

Erie County Executive Mark Poloncarz said the blizzard may be “the worst storm in our community’s history.” He said it was taking ambulances over three hours to do one trip to a hospital. Plows were on the roads, but large snow drifts, abandoned cars and downed power lines were slowing progress.    

Blinding blizzards, freezing rain and frigid cold also knocked out power in places from Maine to Seattle, while a major electricity grid operator warned the 65 million people it serves across the eastern U.S. that rolling blackouts might be required.

Pennsylvania-based PJM Interconnection said power plants are having difficulty operating in the frigid weather and has asked residents in 13 states to conserve electricity through at least Christmas morning. The Tennessee Valley Authority, which provides electricity to 10 million people in the state and parts of six surrounding ones, directed local power companies to implement planned interruptions but ended the measure by Saturday afternoon. The start of the NFL’s Tennessee Titans’ game in Nashville was delayed an hour by a planned power outage.

PJM Interconnection, which covers all or parts of 13 states and and Washington, D.C., also warned rolling blackouts might be required.

In North Carolina, 169,000 customers were without power Saturday afternoon, down from a peak of more than 485,000, but utility officials said rolling blackouts would continue for “the next few days.”

Those without power included James Reynolds of Greensboro, who said his housemate, a 70-year-old with diabetes and severe arthritis, spent the morning bundled beside a kerosene heater with indoor temperatures “hovering in the 50s.”

In Jackson, Mississippi, officials Saturday said the city’s water system – which partially collapsed in late August – was experiencing “fluctuating” pressure on Saturday afternoon amid frigid temperatures.

Some residents in Mississippi’s capital city may temporarily experience low water pressure, officials warned. Leading up to the “arctic blast” that brought dangerously cold air to Jackson, Mayor Chokwe Antar Lumumba warned that the city’s the water distribution system remained a “huge vulnerability.”

Ticket prices at Soldier Field in Chicago Saturday plummeted faster than the temperature, with some seats going for $10 on third-party sites to see the Bears take on the Buffalo Bills. The temperature at kickoff was 9 degrees, with a minus-12 wind chill. It was Buffalo’s coldest road game by temperature since at least 1967.      

In Montana, it’s been minus 40 degrees or worse for much of the week, with ranchers attempting to keep their cattle safe. 

On the Ohio Turnpike, four died in a massive pileup Friday involving some 50 vehicles. A Kansas City, Missouri, driver was killed Thursday after skidding into a creek, and three others died Wednesday in separate crashes on icy northern Kansas roads.

A utility worker in Ohio was also killed Friday while trying to restore power, a company said. Buckeye Rural Electric Cooperative said the 22-year-old died in “an electrical contact incident” near Pedro in Lawrence County.

A woman in Vermont died in a hospital Friday after a tree broke in the high winds and fell on her. Police in Colorado Springs said they found the dead body of a person who appeared to be homeless as subzero temperatures and snow descended upon the region. In Madison, Wisconsin, a 57-year-old woman died Friday after falling through the ice on a river, the Rock County Sheriff’s Office announced.

In Lansing, Michigan, an 82-year-old woman died after being found Friday morning curled up in the snow outside of her assisted living community, Bath Township police reported. A snowplow driver found the woman as temperatures hovered around 10 degrees.

Kentucky Gov. Andy Beshear said one person died in a traffic accident attributed to the weather in western Kentucky and a homeless person died in Louisville.

Along Interstate 71 in Kentucky, Terry Henderson and her husband, Rick, were stuck in a massive traffic jam caused by several accidents for 34 hours. The truck drivers weathered the wait in a rig outfitted with a diesel heater, a toilet and a refrigerator but nonetheless regretted trying to drive from Alabama to their home near Akron, Ohio, for Christmas.

“I wish we should have stayed,” said Terry Henderson, after they got moving again Saturday. “We should have sat.”

The storm was nearly unprecedented in its scope, stretching from the Great Lakes near Canada to the Rio Grande along the border with Mexico. About 60% of the U.S. population faced some sort of winter weather advisory or warning, and temperatures plummeted drastically below normal from east of the Rocky Mountains to the Appalachians, the National Weather Service said.

In Mexico, migrants camped near the U.S. border in unusually cold temperatures as they awaited a U.S. Supreme Court decision on pandemic-era restrictions that prevent many from seeking asylum. Dozens of migrants were also living and sleeping on streets of the Texas border city of El Paso in subfreezing temperatures waiting for shelters to open. Most were donning donated winter clothing they received from empathetic local residents and volunteers, 

Forecasters said a bomb cyclone — when atmospheric pressure drops very quickly in a strong storm — had developed near the Great Lakes, stirring up blizzard conditions, including heavy winds and snow.

Western New York often sees dramatic lake-effect snow, which is caused by cool air picking up moisture from the warm water, then dumping it on the land. But even area residents found conditions to be dire on Christmas Eve.

Latricia Stroud said she and her two daughters, 1 and 12, were stranded without heat or power in their Buffalo house since Friday afternoon, with the snow too deep to leave.

“I have to go over a snowbank to get out,” Stroud told the AP. “There’s a warming center, I just need a ride to get there.”