A densely populated swath of the Northeast was preparing for winter's harshest thump yet, a fast-moving storm that could bring more than a foot of snow, strong winds and coastal flooding.
American Airlines and Southwest said that they were doing pre-emptive cancelations on Thursday for the East Coast ahead of the storm. On Wednesday, 44 flights were canceled at O'Hare International Airport and two were canceled at Midway Airport.
Some places were poised to experience an atmospheric yo-yo: Philadelphia and New York hit 60 degrees on Wednesday, were expecting at least a half-foot of snow on Thursday and were bracing for bitter cold temperatures Thursday night.
"This is going to be a big punch," said Benjamin Sipprell, a meteorologist with the National Weather Service in Taunton, Massachusetts. "It's originating in the Ohio River Valley and starts cranking as it comes across Appalachia."
The storm was expected to hit eastern Pennsylvania and northern New Jersey with rain early Thursday morning, before changing over to snow in time for the morning commute.
The weather service predicted some parts of the Boston area and eastern Maine would get 12 to 18 inches of snow, New York City 8 to 12 inches and the Philadelphia area 4 to 8 inches.
Near whiteout conditions were possible, with snow expected to fall at a clip of 2 to 4 inches per hour at the storm's height. The weather service issued a blizzard warning for some coastal areas.
Airlines were bracing for a troublesome day: The flight-tracking site FlightAware.com said more than 2,000 Thursday flights had been canceled as of Wednesday afternoon.
High winds moving in on the storm's heels could bring gusts of up to 50 mph, leading to power outages. Temperatures were also forecast to drop into the 20s across much of the region.
Many communities announced parking restrictions in advance of the storm, and some school systems canceled classes on Thursday, including Boston and Providence, Rhode Island. Connecticut canceled most court activities on Thursday.
WLS contributed to this report.
Flights canceled ahead of snow storm in Northeast US