Winter Storm Quinn began pounding the Big Apple and surrounding areas Wednesday afternoon with heavy snowfall, powerful lightning strikes and roaring thunder.

The storm is expected to intensify — with snow falling at a rate of 1 to 2 inches an hour — and may leave up to a foot in the city.

“Once it picks up, it doesn’t matter what time of the year it is, it’ll stick to the pavement, especially after the sun begins to lower,” said Accuweather meteorologist Carl Erickson.

Meteorologists reported flashes of lightning at the World Trade Center, Holland Tunnel and elsewhere as part of “thundersnow,” where layers of unstable air moving upward increase snowfalls and cause thunderstorms.

“When you have these really intense snow bands, it is possible to get thundersnow,” Erickson said.

New Yorkers said they heard thunder in parts of Brooklyn, including Park Slope and Greenpoint, and in Soho, the West Village and even on the Upper West Side.

Mayor Bill de Blasio — who decided not to cancel schools — said additional personnel will be on hand to help with dismissal and after-school pickups.

“When we balance all the factors, yes, I think we made the right decision,” he said.

At a morning briefing, he announced that four NYCHA developments were currently without heat or hot water.

He also asked that New Yorkers go home early if they could to avoid intense afternoon rush-hour snow.

Subways were running normally Wednesday morning but express service was expected to taper off as the snow increased. Metro-North, which was operating on a reduced weekday schedule, was to start running hourly after 8 p.m. Wednesday.

“We’re prepared for what’s about to hit us this afternoon,” MTA Chairman Joe Lhota said during a morning briefing.

Airports were also hit hard by the storm, with about 2,000 flights canceled in the New York area across JFK, Newark and LaGuardia, according to FlightAware.

Hudson Valley counties, which were already hit hard in last week’s storm, could see up to 2 feet of snow. More than 25,000 customers in the Lower Hudson Valley were still without power since last week’s nor’easter.

“Far too many New Yorkers are still without power,” said Public Services Commission chair John Rhodes, who called the outages “severe and prolonged.”