Some of the U.S.'s biggest cities braced for what's expected to be another mammoth snowfall and blizzard-like conditions in the Midwest and the Northeast — with as much as a foot and a half forecast through Friday.
Winter storm warnings stretched from Chicago through the New York tri-state region into New England — affecting an area home to more than 100 million people.
Flights out of PDX to Chicago and New York were starting to be cancelled Thursday morning.
Snow began to fall in Boston, the first major city on the East Coast to be hit, at around 1:30 a.m. ET on Thursday.
"It's going to be a long-duration event," said Michael Palmer, lead meteorologist at The Weather Channel. "The wind is going to whip around the snow and reduce the visibility, creating near-blizzard conditions in Boston, much of Connecticut and then down maybe as far south as New Jersey and even New York City."
A Blizzard Warning is in effect for Coastal Plymouth County & Cape Cod. Otherwise here is the latest info: pic.twitter.com/CtmgBNVc4U— NWS Boston (@NWSBoston) January 2, 2014
The National Weather Service issued a blizzard warning on Long Island in New York beginning at 6 p.m. Thursday, predicting inch-an-hour snow with 45 mph winds during the worst of it Thursday night. Blizzard conditions also are warned for Cape Cod and coastal Massachusetts.
"It's going to be a pretty significant storm, which will cause major travel disruption for a lot of people early in the new year," said Dave Houtz, senior meteorologist at The Weather Channel. "Any untreated roads will be a real mess."
New York Gov. Andrew Cuomo warned that travel would be tricky in the coming days.
"We are telling people, prepare for road closings and take mass transit," he told reporters in a Wednesday conference call about the storm.
In New York City, which was warned to expect 5 to 8 inches of snow through Friday, the administration of newly minted Mayor Bill DeBlasio said it would do its best to keep outdoor subway, Long Island Rail Road and Metro-North trains moving, calling out the Metropolitan Transportation Authority's ice-busting equipment.
Bus riders might not be so lucky: If roads become impassable, bus service will be suspended, the MTA said.
Boston Mayor Tom Menino — in his last official act in office — pre-emptively declared a snow emergency for Thursday and closed the city's schools Friday as weather models pointed to up to 18 inches of new snow.
"What a New Year's gift, to receive one last snowstorm as mayor," Menino said Wednesday.
Buffalo was also predicted to get a 12- to 18-inch wallop, and accumulations of 8 to 12 inches were expected in areas of Vermont, New Hampshire and Maine.
Behind the snow comes a blast of cold. The high temperature in New York City on Friday will be in the teens, with wind-chill values as low as minus-5. Upstate New York and parts of New England will see sub-zero highs and wind chills near minus-30.
What changed the forecast so drastically from Tuesday, when meteorologists said the storm wouldn't be a big deal, was the expected convergence of three separate low pressure systems roaring in from the south and the east.
They're hauling warm, wet air on a course straight for the frigid Northeast, said Greg Postrel, a forecaster for The Weather Channel.
"That's setting up for a big snowstorm for New England," Postrel said — "big" as in near-zero visibility and howling winds with wind chills well below zero.
The storm system was already walloping Detroit, which were under several inches of snow Wednesday, with 5 to 8 inches more on the way.
The main part of the snowfall had moved on from Chicago, but The Weather Channel's Palmer warned that winds there would pick up on Thursday morning.
And the city was set to experience bitterly cold weather in the coming days, warned NBC Chicago meteorologist Cheryl Scott.
More than 600 flights due in or out of Chicago's O'Hare International on Wednesday had been canceled by 10 p.m. ET, according to the flight-tracking website FlightAware.