"Gravity wave" powered late-season snowstorm

Near the height of the most disruptive storm of the winter, one that became a daylong nuisance throughout the region, high drama was playing out in the skies above South Jersey.

Just before midnight Sunday, meteorologists said, a band of rapidly rising air - part of what is known as a "gravity wave" - developed in the upper atmosphere from eastern Virginia into eastern New Jersey. And this was a particularly potent one.

For the next few hours, it generated heavy snow in South Jersey, with 10.5 inches in Hammonton by daybreak, and powerful wind gusts of 60 m.p.h. in Atlantic City and 59 m.p.h. in Cape May. By early morning, 20,000 customers would be without power. In all, New Jersey state police would report 500 accidents, and Gov. Corzine would say the storm could cost the state up to $7 million.

Meanwhile, the wave temporarily would shut off snow to areas to the west, said Louis W. Uccellini, director of the National Center for Environmental Prediction, considered by government and private meteorologists as one of the nation's foremost experts on winter storms.

We now know that the snow did come back as the storm entered a second phase at daybreak. It featured occasionally heavy snow throughout the morning just about everywhere, and a stinging north wind that blew the white powder back over roads, cut visibility, and sculpted modest drifts. All the while, temperatures hovered in the road-salt-resistant 20s. The snow even set a modest record in Philadelphia.

It won't get past the mid-20s today, but the ever-strengthening March sun should melt some of the snow and restore black to the roads. With a hard overnight freeze expected, many schools planned to open late this morning, but that could be viewed as progress.

Once again yesterday, all Philadelphia schools were closed, as were hundreds of others. The city gave up on trash collection, and said to expect a one-day delay in trash and recycling pickups the remainder of the week.

With the storm affecting an area from southern Virginia to southeastern Canada, "a few hundred" flights in and out of Philadelphia International Airport were canceled, spokeswoman Phyllis VanIstendal said.

SEPTA reported daylong 15-minute delays on Regional Rail, and Amtrak had to cancel or cut back on a dozen Northeast Corridor trains, spokeswoman Karina Romero said.

Its biggest problem was on a train from Boston to Newport News, Va., she said. The train got stuck behind a derailed freight train just south of Richmond. The weather got so bad that the train couldn't back up and go to snowy Richmond. The 140 passengers ended up arriving 16 1/2 hours late in Newport News. No one was injured, or happy.

Though the snow stopped for a few hours during the early morning in most areas here, giving the plows a chance to make progress, motorists had more than their share of adventures. The snow's revival came just in time for the morning commute, and persisted even through a noontime sun.

Shortly after 11 a.m., a tractor-trailer jackknifed on the Schuylkill Expressway near Gladwyne, forcing the closing of westbound lanes for more than an hour. Another jackknife incident closed two southbound lanes of I-295 in Burlington County around 10 a.m., and a disabled truck blocked the Vineland, N.J., exit of Route 55 for a while.

The storm might have failed to rise to the direst predictions, but the snow totals were impressive - generally, 6 to 8 inches in the Pennsylvania suburbs, more in South Jersey - and of some statistical note.

Officially, the 8.3 inches measured Sunday night and yesterday at Philadelphia International was the second-highest of the season, bested only by the 8.4 of Feb. 3 and 4. The 5.6 inches measured yesterday broke the March 2 daily record, 5 inches, set in 1914.

And while this won't be remembered as a particularly ferocious winter, it is the first in more than 30 years to have two snowfalls of 8-plus inches.

All that said, Radnor's Laurie Katz, 52, was not impressed. "I grew up in Massachusetts and New Hampshire," said Katz as she worked an elliptical trainer at Club la Maison in Wayne. "This was nothing to me."

The effects of the storm might have been worse in the western suburbs if not for the gravity wave over New Jersey that held down nighttime accumulations, Uccellini said.

He said the atmosphere in a storm behaves not unlike a stormy ocean, with rising and falling waves. Snow forms when warm air rises over cold air, and when air is rapidly rising, it snows heavily. Meanwhile, the area to the west of the wave crest has to sink, aided by the pull of gravity, and that has a drying effect.

Gravity waves are a relatively recent discovery, Uccellini said, and not easy to forecast - or find. "Those waves are superimposed on the larger-scale feature, and they are very hard to track," he said.

Once this particular wave became established, snowfall diminished to the west. For example, while snow was hammering the eastern shore of Maryland and South Jersey, Washington, D.C., actually canceled its snow emergency. As Philadelphia did, however, Washington ended up getting more snow during the day yesterday.

Without the waves, the accumulation amounts likely would have been spread more evenly.

As it turned out, the strongest winds and widespread power outages were confined to areas near the Shore, along with the highest snow totals, up to 13 inches.

By contrast, Peco Energy reported only scattered outages in the suburbs. The most significant one occurred in Chester, where power was knocked out at the municipal building for 21/2 hours starting at 6:30 a.m.

No more significant snows or high winds are in the forecast.

But with the weather turning progressively warmer through the weeks, the outlook calls for outbreaks of wet pants legs - and very dirty vehicles.