Central Park hit an almost-record-high 66 degrees on Wednesday, sending New Yorkers into the streets in T-shirts and shorts on a day when the high would normally be around 40 degrees. The last time it had gotten that warm on Jan. 4 was in 1950.

Throughout the December holidays, the weather induced a bit of whiplash: On Christmas Eve, temperatures hovered in the single digits as a blast of Arctic air snarled air travel in much of the country.

By New Year’s Day, though, chilly drizzle had given way to clear skies and pleasant temperatures in the 50s. Swimmers from around the city gathered in Coney Island for the annual Polar Bear Plunge, which felt markedly less polar than in a typical year. Revelers in costumes and festive regalia beamed as the sun beat down on them.

“It’s very unusual,” said Bryan Ramsey, a meteorologist with the National Weather Service. “What makes it so interesting is what we saw right before Christmas — that was way below average — so it was really interesting to see that swing.”

But he added that it will be back to business as usual in the Nw York area soon enough. Local temperatures are expected to dip into the 30s in the next few days, he said.