For Philadelphia, no predictions of a repeat of last winter

After an unprecedented six-month run of warmth, the atmosphere has assumed a November-like chill, and some meteorologists foresee a brisk start to the cold and snow season.

But the early consensus is that the winter of 2010-11 around here should be a whole lot lighter on snow, supermarket panic, and history than its monstrous predecessor.

"If you want snow this year," said Mike Halpert, deputy director of the federal government's Climate Prediction Center, which released its winter outlook Thursday, "you're better off going out to the West."

In the winter forecast it updated Thursday, AccuWeather Inc., the commercial service based in State College, Pa., called for above-normal winter temperatures in the Philadelphia region starting in late December, with snowfall a tad below normal - about 20 inches. That's similar to the call it issued last month, and the one by Commodity Weather Group, a forecasting service in Washington.

The climate center waffled on the winter outlook for the Mid-Atlantic and Northeast, characterizing it as a toss-up.

But government and private forecasters agreed that, elsewhere, this is likely to be a winter of extremes, with bitter cold possible in the Pacific Northwest and potentially dangerous drought in the South.

A few cautionary notes for snow lovers and loathers: It's only October; long-range prediction is one of meteorology's shakiest limbs, and no one foresaw last winter's record Mid-Atlantic snows.

But this winter the forecasters believe they have a strong signal in the thermal revolution that has occurred over millions of square miles of the equatorial Pacific.

The unusually warm Pacific surface temperatures, or El Niño, that contributed to last winter's cosmic snows have been routed by decidedly chillier waters, or La Niña.

It's as though nature has been dumping massive buckets of ice into the ocean out that way.

The profound temperature changes over such a vast area are expected to disrupt upper-air patterns across North America in such a way as to keep whopper snowstorms and prolonged cold away from Philadelphia. However, it may take several weeks for the effects to mature.

Any promised warmth won't be in evidence the next few days with daytime highs in the upper 50s and nights near 40, more typical of early November. And after a warm-up, a Halloween chill may follow, said Joe Bastardi, AccuWeather's long-range forecaster.

October temperatures should finish close to normal (57.2 degrees) in Philadelphia, and that would represent a dramatic change from what we've experienced so far this year. The last six months represented the warmest March 1 to Sept. 30 period on record in Philadelphia. As Glenn Schwartz, meteorologist at NBC10, pointed out, each of those months finished in the warmest Top 10 since record-keeping began in the 1870s.

November and December actually could even end up on the cold side, Bastardi said. Winter, he said, "will get off to a pretty good start."

"I wouldn't give up on a white Christmas."

Similarly, the Commodity Group and WSI Corp., a Massachusetts forecasting service, have predicted a colder-than-normal December.

As the La Niña effects ripen, however, January and February should be kinder to heating budgets, Bastardi said.

Right now, the La Niña event is classified as "strong," and it's likely to stay that way throughout the winter, said Halpert. Strong La Niñas favor below-normal snow from Washington to New York, he said. But other forces driving cold and snow in the Northeast, such as pressure patterns in the North Atlantic, are unpredictable beyond a few weeks.

For what it's worth, in the last 60 years none of the six winters that coincided with a strong La Niña (1949-50, 1955-56, 1973-74, 1975-76, 1988-89, and 1999-2000) has been inducted into the Philadelphia Winter Lovers Hall of Fame.

In the La Niña winter of 1949-50, the official Philadelphia total was 1.9 inches of snow. No supermarket panic was reported.

"Lovers of winter got spoiled last year," said Bastardi, who had correctly predicted above-normal snowfall in Philadelphia for the 2009-10 season - but nowhere near the historic 78.7 inches. "You're not going to see anything like that this year."