Philadelphia weather: Nor'easter coming; expect winds, coastal flooding

The Vatican's St. Peter's Square is one of the world's most famous venues, but not necessarily for its snowball fights.

Yet, grown human beings were throwing snowballs there Monday. Driving frigid temperatures into western Europe and crowning the Eternal City with up to 6 inches of snow, the atmosphere served notice it was ready for a spell of old-fashioned March-like volatility..

This region will get a taste of it by the end of the workweek as a powerful coastal storm off New Jersey is forecast to generate at the least minor flooding along the Shore.

"We're going to see high swells along the Jersey coast and Long Island," said Max Vida, a meteorologist with AccuWeather.

Exacerbating conditions would be the full moon and the fact that the storm is going to stall off the coast, thus beach-eroding waves are possible Friday into Saturday, according to the National Weather Service.

For the first time in several weeks, something is out there in the North Atlantic to keep a storm from moving quickly.

That's a blocking area of high pressure centered near Greenland that will prevent the nor'easter from racing out to sea. Such blocking has been absent recently.

One symptom of its return is the European cold that gave us that white blanket over St. Peter's Square and has Ireland bracing for a rare blizzard.

The pressure pattern — known technically as the negative phase of the North Atlantic Oscillation, or NAO — is one that snow-lovers have been waiting for. It allows cold air to plunge into the Northeast and can force coastal storms to stay awhile.

But it evidently has set up too late to requite their desires around here, said Vida. Unless something changes drastically — and for an excellent analysis of the players involved, see Chad Shafer's write-up in the "long term" section of the weather service morning discussion — snow is about out of the question.

The Poconos might see some wet flakes, but the Philadelphia region is due for another soaking rain, maybe 1 to 2 inches,  this time accompanied by raw winds and temperatures in the 40s.

Had this pattern set up a few weeks earlier, said Vida, well, the dairy cases might have been cleaned out.

As it is, this month is about to end as one of the top 5 warmest Februaries in Philadelphia and the first winter month this season to fall short of average snowfall.