A monster storm barreling across the United States had killed at least 11 people Monday, prompting warnings to stay off the roads, mass flight cancellations and power outages after a weekend of misery.
The storm dumped snow, sleet and freezing rain across swathes of the country from Texas to New England, with temperatures set to fall dangerously low this week.
New York City Mayor Zohran Mamdani said five people were found dead outside over the weekend, telling reporters "there is no more powerful reminder of the danger of extreme cold”.
In Texas, authorities confirmed three deaths, including a 16-year-old girl killed in a sledding accident.
Two people died in Louisiana from hypothermia, the southern state's health department said.
Meanwhile, one person was killed and two others injured on Saturday during a winter weather related collision in southeast Iowa, according to local State Patrol.
The brutal storm system is the result of a stretched polar vortex, an Arctic region of cold, low-pressure air that normally forms a relatively compact, circular system but sometimes morphs into a more oval shape, sending cold air spilling across North America.
Scientists say the increasing frequency of such disruptions may be linked to climate change, though the debate is not settled and natural variability plays a role.
While the storm system was expected to drift away from the East Coast into the Atlantic, a blast of Arctic air was rushing in from Canada behind it, prolonging sub-freezing temperatures for several more days, the National Weather Service (NWS) 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 Centre. "But the big picture story is the extreme cold, it's lasting into early February."
Almost 200mn 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 -4° Fahrenheit (-20° Celsius) Monday, and New York City, Washington DC and Boston all faced single-digit temperatures through much of the week ahead.
More than 800,000 homes and businesses across the southeastern US 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 US flights canceled on Sunday – the most of any day since the onset of the coronavirus (Covid-19) pandemic in 2020.
About 3,900 flights within, into or out of the United States were canceled Monday as of 9.15am ET (1415 GMT), according to the tracking website FlightAware.
US Transportation Secretary Sean Duffy told CNBC that he hopes airports will be "back to normal" by Wednesday.
In Bonito Lake, New Mexico, residents were shoveling out after 31” of snow.
New York City's Central Park received 11.4”, while Logan Airport in Boston saw 18.6”, the NWS’s Santorelli said.
New York Governor Kathy Hochul said she had mobilised National Guard troops in New York City, Long Island and the Hudson Valley to assist with the state's emergency storm response.
Announcing that schools would be shut for a remote school day, New York City's Mayor Mamdani quipped: "I know that this may disappoint some students, so if you do see me, feel free to throw a snowball at me."
Still, despite the disruptions, the winter conditions were fun for many, including in Washington DC, where a huge crowd gathered on Sunday for a raucous impromptu snowball fight in Meridian Hill Park.
Families brought sleds to Capitol Hill, where children zoomed down the steep slope below the white-domed seat of the US Congress.
