The eastern United States was in a panic ahead of what forecasters called a "potentially paralyzing" blizzard, sparking flight cancelations and the looming shutdown of Washington's public transportation system.
The US capital and the surrounding area could see up to two feet (61 centimeters) of snow accumulate in a short time from Friday to Saturday, coupled with fierce winds and blinding squalls, weather experts said.
With authorities warning the storm could bury Washington under more snow than it has seen in nearly a century, officials announced they would take the unusual step of closing down the city's rail and bus system from Friday night until Monday morning.
The Metro system - the second busiest in the United States after New York - serves about 700,000 customers a day in Washington, Maryland and Virginia.
It is likely the longest closing in the system's 40-plus year history, The Washington Post reported.
Heavy snow was expected across at least 15 states, with icy rain and coastal flooding in other areas, according to the Weather Channel.
The National Weather Service (NWS) issued a blizzard warning for Washington and said New York could catch the tail end of the storm as the weekend progresses.
"Heavy snow and blowing snow will cause dangerous conditions and will be a threat to life and property," the NWS warned.
"Travel is expected to be severely limited if not impossible during the height of the storm Friday night and Saturday."
NWS director Louis Uccellini said the system had "the potential of being an extremely dangerous storm that could affect over 50 million people."
"We are talking about a potentially paralyzing storm that is already setting up," he told reporters.
Ahead of the first snowflakes, American Airlines said it was canceling hundreds of flights, including at Washington's two airports on Saturday. All flights on that day will also be scrapped in Baltimore and Philadelphia, a spokeswoman said, adding that service would likely resume Sunday and be reduced Friday.
United Airlines announced it would be suspending flights at Washington's Dulles and other Mid-Atlantic airports starting on Friday afternoon.
Washington Mayor Muriel Bowser issued a state of emergency and called off school Friday.
"I've lived in DC most of my life and I don't know if I've lived through a forecast like this. It's an extremely large storm," she said.
States of emergency were also declared in neighboring Virginia and Maryland.
'Warm and toasty'
The US capital was already struggling after Wednesday snow flurries left traffic at a standstill, even snaring President Barack Obama's motorcade, which spent more than an hour navigating the icy streets from Andrews Air Force Base to the White House - normally a trip of 20-25 minutes.
"We should have been out earlier with more resources," Bowser admitted.
Asked how Obama planned to weather the big storm, White House spokesman Josh Earnest said Thursday, "My guess is he will stay warm and toasty inside the White House."
If the blizzard dumps as much snow in Washington as forecast, it could surpass a record set in 1922 by a storm that dumped 28 inches over three days and killed 100 people after a roof collapsed at a theater.
Since Wednesday residents have been flocking to supermarkets to stock up on food and snow shovels.
'First big storm'
The NWS said it was unclear if snow would fall through early Saturday in the corridor stretching from New York City to Boston, which saw massive amounts of snowfall last winter.
New York Mayor Bill de Blasio, however, told reporters that his city was preparing for up to 12 inches of snow, as he issued a hazardous travel advisory for the weekend.
"We're bracing for the first big storm of the winter. I want to let my fellow New Yorkers know we're prepared, the agencies here are ready for what's coming up ahead," de Blasio said.
He said more than 575 salt spreaders would be pre-deployed on Friday evening and that the city had 303,000 tons (approximately 275,000 tonnes) of rock salt on hand.
Washington had more than 200 plows and 39 tons of salt at the ready, Bowser said.
Further south, "significant icing is likely for portions of Kentucky and North Carolina," NWS said.
Get out those sleds
Many kids however were excited about the snow, and parents across the region traded tips on where to take them sledding once the blizzard died down.
One option will be the grounds of the US Capitol, where the US Capitol Police said they were lifting a decades-old sledding ban.
The frigid weather marks a stark departure from what has otherwise been a mild winter along the eastern seaboard.
Just a month ago on Christmas Eve, the NWS reported that temperatures in New York's Central Park peaked at 72 degrees Fahrenheit (22 Celsius), the warmest ever for the day since records began in 1871.