A spring snowstorm swept through the Northeast on Wednesday, the fourth nor’easter of the month.

A foot or so of snow was expected from the suburbs of Philadelphia to parts of New York City to coastal Connecticut and Long Island, with significant snow from Washington to Boston.

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More than 4,000 flights were canceled, and LaGuardia Airport suspended all flights.

New York City schools will be open Thursday — they were closed Wednesday — but Boston schools will be closed.

How Much Snow?

Nearly 7 inches of snow had fallen in parts of New York City by mid evening, and there was more to come.

“An inch an hour until midnight or 1 a.m.,” Jay Engle, a meteorologist at the National Weather Service’s New York office, said around 8 p.m.

That could bring snowfall totals in the city to a foot or so, before the storm tapered to a close in the wee hours of Thursday. It would be the biggest snowfall ever to hit New York City in springtime, breaking the record of 10 inches set on April 3, 1915.

The morning commute in New York could be sloppy, with possible scattered snow showers, but no heavy snow.

In Washington, the snow had slowed by Wednesday evening. Less than half a foot of snow was recorded in most of New Jersey, although the forecast predicted up to several inches could fall there overnight. In rural Pennsylvania, snow totals exceeded a foot in some places.

In Boston, it wasn’t snowing yet Wednesday evening when Mayor Martin J. Walsh canceled classes at public schools for Thursday.

Forecasters predicted up to 9 inches of snow in Boston by Thursday morning, but their models did not agree, and many revised their predictions downward and said the city could receive as little as 4 inches. The National Weather Service in Boston counseled patience over Twitter, assuring that the snow would come in the wee hours.

— ANNIE CORREAL and KATHARINE Q. SEELYE

Travel Woes Mount

New York City’s subways were running, but some lines switched to local service.

New Jersey Transit suspended bus service at 3 p.m.

Railroads, including Metro-North, New Jersey Transit and Amtrak were operating on limited schedules. Long Island Rail Road was still running on a regular schedule.

One person was killed in New Jersey in a bus crash the governor attributed to the storm.

The storm hobbled airports, stranding passengers as they scrambled to find alternative options or lodging. Hundreds of incoming and outbound flights were canceled at every major airport in the Northeast.

Renu Khandelwal, 45, and her daughter Muskaan, 15, were stuck at LaGuardia in New York after their flight home to Fayetteville, Arkansas, was canceled. “There are no hotels available,” Khandelwal said as she scrolled through her phone.

So she and her daughter were gearing up to camp in the terminal alongside their suitcases.

Nearby, Sharon McCormick, 55, and her husband, John, were clicking on hotel links only to have “not available” pop up over and over again. “I’d be willing to stay here,” Sharon McCormick said. “Hopefully the bar just stays open.”

— JOHN SURICO and JONATHAN WOLFE What Is Up With All These Storms?

Wednesday’s storm was the fourth serious snow to wallop the Northeast this month — the others were on March 2, March 7 and March 13.

This is an odd occurrence in March — regionwide storms of this size typically develop only about once a year, said the director of the National Weather Service, Louis W. Uccellini.

But every few years, storms do tend to come in bunches, Uccellini said. “The episodic nature of these storms is not weird,” he said. “It’s actually a characteristic of these storms.”

(Uccellini knows whereof he speaks. He wrote the book — “Northeast Storms, Vols. 1 and 2” — on the subject.)

The culprit, he explained, is something called the North Atlantic Oscillation, which is related to airflow over this part of the planet. When the NAO is positive — as it was from December to February — the air moves fast and storms do not have time to build up a lot of power.

But in March, the NAO went negative. That means the flow gets blocked. “You get a trough that sits off northeast Canada, or between Canada and Greenland, and it tends to lock in cold air in the northeastern U.S.,” Uccellini said.

And because the air over the North Atlantic, to the south and east of the Northeast, stays warm and moist, Uccellini said, that contrast between cold air over land and warm air over sea “can be conducive to rapid cyclogenesis.” That is a fancy way of saying, “It makes big snowstorms.”

This is likely to be the last big snow of the season. The NAO is predicted to go neutral-to-positive by the end of the week.

— ANDY NEWMAN

Central Park Belongs to the Brave Ones and Their Dogs

Standing in Central Park with a cluster of children around him, Matt Hoek pulled a list from his pocket: snow-covered bench, snow-covered taxicab, bus with chains, pine cone. He had the children — his two daughters, who are 2 and 5, and some of their friends from around their Upper West Side neighborhood — on a snow-day scavenger hunt.

“That was a big find for us — a person on a CitiBike,” Hoek said as the group paused so one of the boys could climb a tree. “We actually found one.” (This was before CitiBike shut down for the day at 1 p.m.)

Central Park was sparsely populated, snow caked the lawns and sidewalks, and stinging winds blew along Jacqueline Kennedy Onassis Reservoir. Still, the runners, dog walkers and tourists held their ground.

“We don’t see snow like this — it’s pretty impressive,” Miguel Navío, visiting from Barcelona, said as he stood near the reservoir.

Some of the dogs looked as if they were being dragged, slinking down as the snow hit their faces. A Labrador retriever wore an annoyed expression as he stepped through the snow to tend to his business. But a scruffy black-haired dog named Holly pranced through the snow with a coat cinched around her torso and a pink ball in her mouth.

Her owner, Caroline Koeppel, was similarly delighted. “It’s beautiful,” she said, looking out at the nearly empty expanse of the Great Lawn. “My dog has the park to herself.” She wished for enough snow to be able to cross-country ski through the park. “I’m in here no matter what,” she said.

Holly had started off the walk on the Upper East Side with a shoe for each paw, but by this point she was down to just two as she skittered around with her ball. “There are no squirrels,” Koeppel said. “I think she’s a little disappointed.”

— RICK ROJAS