Snow here, rain there, and in many places a heavy mix of the two: nature threw another cold, wet blanket over the Northeast on Thursday, for the third time this month.

Travel was disrupted at major airports from Philadelphia to Boston, with more than 1,100 flights canceled in the New York area alone by 5 p.m. Officials said that number would probably grow as the winds pick up and temperatures drop into evening.

By late afternoon, the thermometer was still hovering just above freezing in Philadelphia and New York City, and thick flakes signaled what was to come - and what forecasters say will keep coming until Saturday morning.

As a low pressure system off the coast was turning slowly northward and circulating over much of the region, the rain was starting to change into snow inland. Winds were expected to kick up to 35 miles an hour in the Philadelphia region by late Thursday night, when the snow should start to stick, according to Greg Heavener, a meteorologist with the National Weather Service in the Mt. Holly, N.J./Philadelphia office.

Philadelphia has already surpassed its snow record for the winter with the back-to-back storms earlier this month. The new storm was expected to add 7 to 12 inches to the 73-inch tally so far this season.

"It's nice to see when it first starts, but just like everybody else, we're tired of it," said Cap. Kenneth Coalson of the Chester Township police in the Philadelphia suburbs.

In the New York area, the accumulation will vary greatly from west to east. Warm air coming off the Atlantic kept the precipitation mainly in the form of rain on much of Long Island, which may not get more than two inches of snow in all. Manhattan, however, could register as much as a foot of snow, and Passaic, N.J., could receive as much as 15 to 20 inches.

"The rain-snow line is literally over Queens right now," Brandon Smith, a meteorologist for the National Weather Service in Upton, N.Y., said in the early afternoon.

LaGuardia Airport reported delays averaging 4 hours and 10 early in the afternoon, with sloppy conditions. By 5 p.m., delays were down to two hours with 380 flight cancellations, according to a spokesman for the Port Authority of New York and New Jersey.

While delays and cancellations were light at John F. Kennedy International Airport, Newark Liberty International Airport felt the brunt of the weather Thursday, reporting nearly 600 cancellations. Heavy rain at Logan International Airport in Boston were causing 85 minute delays by the early evening.

"This is an incredibly slow moving storm," Mr. Smith, the meteorologist, said. "It's literally going to sit over us for the next two days."

Recent warmer weather and rain had meant that Philadelphians had finally seen the last of the old snow that fell in February. At least they know what to expect.

Captain Coalson of the Chester Township Police said his officers would be out handling accident reports on Interstate 95, and issuing citations for certain recalcitrant snow shovelers. Local laws prohibit the common practice of pushing or dumping shoveled snow in the street for passing plows to deal with; fines for violations can range from $25 to $600. "We don't enforce it until two, three days down the road," Captain Coalson said.

Some residents try to reserve for themselves the curbside parking spots outside their homes that they have laboriously cleared of snow by leaving folding chairs in the spots when the car is not there. "We will collect the chairs and throw them out," Captain Coalson warned.

Staying put might be the answer, since travel seemed to be deteriorating in the Northeast, making travel difficult.

Complicating matters for Amtrak service on the busy Northeast Corridor was a fatal accident believed to be unrelated to weather. A high-speed Acela train from Boston bound for Washington struck two pedestrians on the tracks nine miles south of Philadelphia at 10:28 Thursday morning, according to Tracy Connell, an Amtrak spokeswoman. Ms. Connell said both people died, but that she did not have any further information.

Four mainline tracks were closed while the accident was investigated, and service was not fully restored until 1 p.m. Passengers on the Acela train involved in the accident, No. 2151, were stuck on the train until they could be transferred to Wilmington, Del., on Thursday afternoon to complete their journey.

Amtrak had already canceled eight trains on its New York-to-Albany route because of track repairs needed after a storm in the Hudson Valley on Wednesday. CSX, the freight railroad, owns and maintains those tracks.