Children, dogs and dedicated runners were out early to disturb the blank canvas of snow covering Central Park on Sunday morning, where trees, meadows and pathways were frosted in a wintry icing after New York City’s first substantial snowfall of the season.

The snow fell across the city overnight, picking up steadily in the early morning hours before beginning to taper off from the west around midmorning.

The National Weather Service offices in New York and New Jersey issued winter weather advisories through Sunday afternoon. Winter storm warnings were also in effect for much of New Jersey and southeast Pennsylvania, where up to six inches of heavy snow was expected to accumulate.

In the park, joy reigned. Andrew and Shea LaPlante, visiting the city from Florida, had brought their children, Beau, 8, and Autumn, 5, to the East Meadow to experience the scene.

“It was tough to sleep last night since we were so excited for the kids,” Mr. LaPlante, 42, said. “He hasn’t seen snow since he was a baby, and it’s our daughter’s first time seeing it.”

When Beau’s mother asked him what he thought of the snow, he rated it “infinite out of 10.”

The snow was welcome in a city that has received below-normal snowfall in recent years.

“It feels like a Norman Rockwell painting out here,” said Robert Skelly, 50, who had brought his 10-year-old dog, April, to the park.

As of 1 p.m., 2.7 inches of snow had fallen at Belvedere Castle in Central Park, the official National Weather Service measuring station for the city. That made Sunday the earliest date of the season since 2018 that more than two inches of snow had accumulated in Central Park.

At Kennedy International Airport, 4.6 inches of snow had accumulated by 1 p.m., and there was 2.6 inches of accumulation at LaGuardia Airport.

In a typical winter, the Central Park site records nearly 30 inches of snow, according to the 30-year average from the Weather Service. In recent seasons, totals have not come close to that.

Only a little more than a foot was recorded last winter, which was more than the 7.5 inches measured at the site the winter before, and the scant 2.3 inches the winter before that.

New Yorkers were quick to take advantage of the conditions on Sunday. David Ringer, a volunteer with the New York City Bird Alliance, was out with a group to count birds in Central Park. He noted that a snowy white backdrop can make birds easier to spot — though it also makes them more visible to predators. “The snow will concentrate them around food sources because it covers up a lot of the ground where they normally feed,” he said.

Members of a running club called No More Lonely Runs were singing “New York, New York” while warming up in a circle before a relay through the park. One runner, Keya Shah, 26, said she was happy about the weather: “What’s the point of cold if it doesn’t snow?”

In Brooklyn, the wet snow turned some long stretches of unshoveled sidewalk slippery while coating trees in a sculptural layer of white. People bundled in winter gear trickled from Flatbush Avenue into Prospect Park, which was quiet under its frosty blanket.

Before letting their mixed-breed dog, Maisey, run free, Jennie Portnof and Rebecca Young of Brooklyn paused to take in the wintry scene.

“It looks like Narnia,” Ms. Portnof, 55, said.

Outside an Enterprise Rent-a-Car office on Empire Boulevard, a manager, Ronaldo Carty, alternated between a shovel and a two-wheeled salt spreader to clear the sidewalk and driveway. He did not seem bothered by the labor.

“We haven’t gotten a lot of snow lately, and I think it’s great; I’m excited,” Mr. Carty, 28, said during a break. A cousin of his from Jamaica had just arrived over the weekend. “It’s his first time seeing snow,” Mr. Carty said, adding that before he went to work, “we went outside and got an early snowball fight in.”

The snow overnight came as a cold, fast-moving storm barreled across the Mid-Atlantic region. Places across Connecticut, Delaware, Maryland, New Jersey and Pennsylvania had received between two inches and a foot of snow by Sunday morning.

The system is expected to exit the region by Sunday afternoon, brushing parts of southern New England before moving offshore over the Atlantic Ocean by Sunday evening, said Frank Pereira, a meteorologist with the Weather Prediction Center.

The system brought with it “a shot of cold air,” Mr. Pereira said, and on Monday temperatures across the Mid-Atlantic are forecast to plummet to below normal.

In New York City on Monday morning, temperatures are expected to be in the teens, according to Dominic Ramunni, a meteorologist at the Weather Service office in Upton, N.Y. With the wind, he said, it might feel like the temperature is in the single digits.

“People are going to get a real blast of winter,” he said.

By Tuesday, temperatures across the Mid-Atlantic are expected to be seasonal, and could potentially rise to above normal by Wednesday.

Despite the cold, Keshv Srinivasan, 23, who moved this summer from Texas to the Upper East Side of Manhattan, was thrilled. “I woke up and opened my window and was like, Oh, my God — that was not what I was expecting,” he said. He grabbed a coffee and went to the Central Park reservoir to explore. “Winter’s still novel and exciting to me, but it’s definitely better with snow,” he added.

Molly Longman and Sean Piccoli contributed reporting.