2011 officially Philadelphia's wettest ever - with six weeks left

At 1:33 p.m. Wednesday, 1996 threw in the towel.

With slightly more than half an inch of rain measured for the day, the National Weather Service decreed that 2011 had dethroned the erstwhile reigning champ as the wettest year in Philadelphia weather history.

By then, the precipitation total - including all that melted snow and ice - had reached 56.66 inches at Philadelphia International Airport, besting 1996's record by 0.21 inches, according to Bob Wanton, a weather service meteorologist in Mount Holly. By the end of the day, an additional 10th of an inch had fallen.

The annual average is 41.3 inches. This year's accumulation had blown past that mark by the time Irene's downpours ended Aug. 28.

Even before Wednesday's rain, this had become the wettest 10-year period in 138 years of record-keeping, edging out the 1970s.

Why all the wet stuff - which, incidentally, amounts to 1.1 trillion pounds of liquid falling on the city so far this year?

It is likely related to general worldwide warming, said Art DeGaetano, chief of the Northeast Regional Climate Center at Cornell University in Ithaca, N.Y.

"The atmosphere gets warmer," he said, "it holds more water vapor."

The wet trend, however, hasn't been uniform across the country. Texas and parts of the Southwest have suffered through horrific drought.

Water vapor alone is not enough to set off rain, which requires other conditions. Some of them, including favorable upper-air patterns that have imported generous moisture from the Gulf of Mexico and Atlantic Ocean, have been abundantly present in the Northeast, said Paul Walker, meteorologist with Accu-Weather Inc. in State College, Pa.

In the last 12 months, the Northeast has set a record for the pervasiveness of extreme precipitation, based on analysis by the National Climate Data Center in Asheville, N.C. Annual records also have been smashed already in Harrisburg, Scranton, Williamsport, and Binghamton, N.Y.

In the Philadelphia region, this has been a banner year for storms, stream flooding, and power outages.

August, the month of Irene, was the wettest month ever in the city, featuring about a half-year's worth of rain. August and September, the month of Lee, constituted the wettest two-month period.

One thing is certain: With six weeks to go, 2011 will keep adding to its record.

Said Wanton, "We're counting."