It looks like holiday shoppers could encounter some tough sledding this weekend, with the odds of a significant snowstorm increasing.

The National Weather Service has posted a winter-storm watch for Philadelphia, Delaware County, all of South Jersey and all of Delaware, and the National Weather Service says up to 10 inches is possible in some areas. The heaviest amounts are expected to the south and east of the city, but the recent computer-model runs have been bringing the snow progressively farther north and west, said Jim Poirier, a meteorologist in the Mount Holly office.

The weather service says the odds are better than 55 percent that Philadelphia would get at least 4 inches, with a 30 percent chance of 6.

Meteorologists warn that this could become another full-blown nor'easter with howling winds at the Shore and significant erosion of beaches that already have weathered a brutal fall.

The details remain uncertain - and expect revisions before the snow starts late Friday or early Saturday - but the consensus is that Philadelphia will be getting its first measurable snow of the season.

One important detail is just how far north the heaviest snow penetrates. Accu-Weather Inc., the private service in State College, Pa., says New York and New England may be spared, but meteorologist John Kocet advised that storms of this size often dump heavy snow farther north than expected.

The storm is expected for form in the eastern Gulf of Mexico and migrate to the Atlantic Coast, where it would become a sand-erasing nor'easter.

That has been a familiar scenario the last two months, a pattern related to the El Niño, the expansive area of warm water over the tropical Pacific, that continues to intensify.

Poirier said the pattern so far is reminiscent of the winter of 1997-98, when a strong El Niño energized the coastal storm track into February.

That year, however, Philadelphia received less than an inch of snow as warm Pacific air flooded North America. Now, however, cold air is plentiful, and meteorologists say that will be the case at least until Christmas - when another storm threatens.

Said Poirier: "Thank goodness for global warming."

Contact Anthony R. Wood at 610-313-8210 or twood@phillynews.com