With the snowfall reaching its peak intensity, chances are this will end up as the region's biggest December snow since John F. Kennedy was president-elect and baby boomers were sledding on their Flexible Flyers.

Already, over 10 inches has fallen in portions of South Jersey and Delaware, with 8.8 measured officially at Philadelphia International Airport, which was weathering a day of disruptions.

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Accumulations varied wildly - from 13 inches in Chestertown, Del., to a trace at Allentown – but in general they were heftier to the south of Philadelphia, a reversal of the normal situation.

Rare "thundersnow" – literally a wintry thunderstorm that can wring out a quick couple of inches within an hour – has rocked parts of South Jersey, said Tony Gigi, meteorologist at the National Weather Service in Mount Holly.

Before it's all over tomorrow morning, forecasters were expecting a total of 10 to 15 inches from the city on south, with 6 to 10 more common to the north. Heavy snow was anticipated into tonight as the powerful storm off the coast of Norfolk, Va., intensifies. Gigi said most of the accumulating snow should be over by midnight.

Peak winds up to 45 m.p.h. were possible at the Jersey Shore, where several inches of snow have fallen and several more may be coming. The Shore, hammered repeatedly by nor'easters, needed another storm about as much as the malls needed to lose critical business on the Saturday before Christmas.

Affecting areas from North Carolina to New England – blizzard conditions were reported in Washington - the snow has been a transportation nightmare, with numerous flights in and out of Philadelphia canceled. Anyone planning to fly anywhere should check with the airlines before even attempting to go out into the white mayhem.

"We're doing the best we can with what mother nature's throwing at us," said Mark Gale, the airport's chief executive officer. As of noon, estimated that about 70 to 75 percent of all flights into and out of the airport had been canceled.

SEPTA was reporting 45-minute delays on regional rails, and buses and trolleys were having a hard time getting around the snow-covered streets. The Route 35 bus that navigates the foothills of Manayunk and Roxborough has shut down. All school district activities have been canceled.

In a move that is likely to boost the spirit of pre-game tail-gaters, if not Bud Light sales, the Eagles have decided to move back the start of Sunday's game with the San Francisco 49ers (they must love this weather) until 4:15 p.m.

Mayor Nutter, confronting his first major snowstorm as mayor, warned that the storm would tax the city's snow-fighting resources and made a direct plea to city residents. "We need help and support from all Philadelphians," he said. "First if you really don't need to go out please don't go out.. . . Second, if you do have to go out, pleases be careful."

The first flakes sifted across the region around 3 a.m., and with temperatures in the 20s, the snow started sticking right away.

One reason for the variations in accumulations was the fact that some areas were caught under bands of heavy snow where it piled up in a hurry. Thundersnow also added to some totals.

The official Philadelphia total could rival or surpass the storms of Dec. 24-25, 1966, 12.7 inches, another storm characterized by thundersnow, and Dec. 11-12, 1960, when 14.6 inches fell Sunday into Monday.

Unlike this one, the 1960 storm was an ambush, and disrupted the workweek.

This one was well-advertised, and occurring on a Saturday, the impact will be less. However, the timing couldn't be worse for the region's shopping malls on what should have been one of the busiest days in the busiest season.

Nutter said he was sympathetic to the potential shopping impacts. "We're very concerned about retailers and all business retailers through the city. We understand that. That's why I'm encouraging people to take mass transit and SEPTA. You can still get to where you're going to get to."

Meanwhile, for those who do want to venture out on the roads, the Parking Authority has reduced all its rates to $5 in their garages through Sunday.

As state crews worked on both sides of the river, the Philadelphia Streets Department was counterattacking nature's assault with its armada of 360 salt trucks and plows.

Some people were just determined to get out there. Several folks showed up at 8.30 a.m. at the Main Line YMCA in Ardmore for their weekly "iron man" aerobics class, taught by Wharton professor Anne Greenhalgh.

Among them was Shelly Herndon, who walked nearly a mile from her Ardmore home to get to class.

"It was fine," she said. "I really wanted to get here and I didn't want to drive."

Contact staff writer Sam Wood at 215-854-2796 or samwood@phillynews.com.

Inquirer staff writers George Anastasia and Dorothy Brown contributed to this article.