The Big Apple was buried in white — from out of the blue!

The snowstorm that wreaked havoc on the city blindsided weather forecasters, who predicted only a light dusting, meteorologists said Friday.

Warm air from the Atlantic Ocean was supposed to turn the snow into rain by around 4 p.m. Thursday — but an unexpected icy blast had it hovering over the city for three extra hours, Accuweather senior meteorologist Bob Larson told The Post.

“It was a relentless unleashing of cold air from the Arctic,” Larson said. “We underestimated how cold it would be because it usually lets up faster this time of year.”

He added, “It hung on stubbornly — and the results weren’t pretty.”

The “sheer intensity” of the big white flakes, which fell at more than 2 inches per hour, left Central Park buried in 6.4 inches instead of the predicted 3 inches, he said.

It brought traffic to a halt in many parts of the city, with busloads of students not getting home until midnight.

“It was blinding, heavy snow. The intensity was far greater than predicted,” Larson explained Friday.

Earlier in the day, Mayor de Blasio blamed “bad luck” and crummy forecasting for the city’s inept response to the storm.

Temperatures are expected to rise to the 40s over the weekend, melting away most of the snow, Larson said.