The Arctic blast is expected to claim more lives after trapping some residents inside houses with heaping snowdrifts and knocking out power to tens of thousands of homes and businesses.
The scope of the storm has been nearly unprecedented, stretching from the Great Lakes near Canada to the Rio Grande along the border with Mexico.
About 60% of the US 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.
Travellers’ weather woes are likely to continue, with hundreds of flight cancellations already and more expected after a bomb cyclone – when atmospheric pressure drops very quickly in a strong storm – developed near the Great Lakes, stirring up blizzard conditions, including heavy winds and snow.
Some 1,707 domestic and international flights were cancelled on Sunday as of about 2pm EDT, according to the tracking site FlightAware.
The storm unleashed its full fury on Buffalo, with hurricane-force winds and snow causing whiteout conditions, paralysing emergency response efforts.
New York governor Kathy Hochul said almost every fire engine in the city was stranded on Saturday.
Officials said the airport would be shut until Tuesday morning. The National Weather Service said the snow total at the Buffalo Niagara International Airport stood at 43in (109 centimetres) at 7am on Sunday.
Daylight revealed cars nearly covered by 6ft snowdrifts and thousands of houses, some adorned in unlit holiday displays, dark from a lack of power.
With snow swirling down untouched and impassable streets, forecasters warned that an additional 1ft to 2ft of snow was possible in some areas through early Monday morning amid wind gusts of 40mph.
Two people died in their suburban Cheektowaga, New York, homes on Friday when emergency crews could not reach them in time to treat their medical conditions, and another died in Buffalo.
Four more deaths were confirmed overnight, bringing the total at that point to seven in Erie County. County executive Mark Poloncarz warned there may be more dead.
“Some were found in cars, some were found on the street in snowbanks,” said Mr Poloncarz. “We know there are people who have been stuck in cars for more than two days.”
Freezing conditions and day-old power outages had Buffalonians scrambling to get to anywhere that had heat amid what Ms Hochul called the longest sustained blizzard conditions ever in the city.
But with streets under a thick blanket of white, that was not an option for people like Jeremy Manahan, who charged his phone in his parked car after almost 29 hours without electricity.
“There’s one warming shelter, but that would be too far for me to get to. I can’t drive, obviously, because I’m stuck,” Mr Manahan said. “And you can’t be outside for more than 10 minutes without getting frostbite.”
Ditjak Ilunga, of Gaithersburg, Maryland, was on his way to visit relatives in Hamilton, Ontario, for Christmas with his daughters on Friday when their SUV was trapped in Buffalo. Unable to get help, they spent hours with the engine running, buffeted by wind and nearly buried in snow.
By 4am on Saturday, their fuel nearly gone, Mr Ilunga made a desperate choice to risk the howling storm to reach a nearby shelter. He carried six-year-old Destiny on his back while 16-year-old Cindy clutched their Pomeranian puppy, following his footprints through drifts.
“If I stay in this car I’m going to die here with my kids,” Mr Ilunga recalled thinking. He cried when the family walked through the shelter doors. “It’s something I will never forget in my life.”
The storm knocked out power in communities from Maine to Seattle. But heat and lights were steadily being restored across the US.
According to poweroutage.us, less than 200,000 customers were without power on Sunday at 3pm EDT – down from a peak of 1.7 million.
Concerns about rolling blackouts across eastern states subsided on Sunday after PJM Interconnection said its utilities could meet the day’s peak electricity demand. The mid-Atlantic grid operator had called for its 65 million consumers to conserve energy amid the freeze on Saturday.
Storm-related deaths were reported in recent days all over the country: 12 in Erie County, New York, ranging in age from 26 to 93 years old, and another in Niagara County where a 27-year-old man was overcome by carbon monoxide after heavy snow blocked his furnace; 10 in Ohio, including an electrocuted utility worker and those killed in multiple car crashes; six motorists killed in crashes in Missouri, Kansas and Kentucky; a Vermont woman struck by a falling branch; an apparently homeless man found amid Colorado’s sub-zero temperatures; and a woman who fell through Wisconsin river ice.
In Jackson, Mississippi, city officials on Christmas Day announced that residents must now boil their drinking water due to water lines bursting in the frigid temperatures, while in Tampa, Florida, the thermometer plunged below freezing for the first time in almost five years, according to the National Weather Service – a drop conducive to cold-blooded iguanas falling out of trees.