Philadelphia Close to All-Time Record Rainfall

August 21, 2011; 5:25 AM ET
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Slow-moving thunderstorm downpours and "training effect" can unleash torrential rainfall and disastrous flooding in some neighborhoods, while other surrounding areas have little or no problems.

August 2011 will go down in the books as the wettest month on record in Philadelphia.

As of midday August 20, 2011, 12.95 inches of rain have fallen at Philadelphia International Airport, where measurements for official records are taken.

According to Expert Senior Meteorologist Carl Babinski, "The wettest month ever was September 1999, when 13.07 inches of rain fell."

"Part of that rainfall was from Floyd," Babinski added.

This month, there have been no tropical systems to boost rainfall, which makes the feat incredible.

This month, a slow-moving, non-tropical storm system was the culprit. The system created a narrow zone of intense rainfall on the 14th over part of the I-95 corridor.

Officially, August 2011 is the wettest August on record, with 10 full days to go. The old record was 12.10 inches set 100 years ago in 1911, according to the National Weather Service in Mount Holly, N.J.

More rain is coming to the Philadelphia area, and for much of the mid-Atlantic and the Northeast in general for that matter.


The next round of general, drenching thunderstorms for the Northeast is coming Sunday. However, spotty thunderstorm activity can occur before and after this event. In addition, the tropics may have a say in rainfall along the Atlantic Seaboard before the month comes to a close.

There is potential for this August in New York City to roll into the top 10, even the top five, all-time wettest months ever. The all-time record for New York City's Central Park is 16.85 inches set in September 1882. As of midday August 20, 2011, 10.92 inches of rain have fallen in the Big Apple for the month so far.

A warm, humid weather pattern, combined with at least a couple of fronts pushing from the Midwest to the Atlantic Seaboard will squeeze out moisture in the form of drenching showers and thunderstorms.

The rainfall will vary greatly from one location to another, which is the nature of summer downpours.

While these tend to be random, the odds of picking up an additional couple of inches, let alone a couple of tenths of an inch, of rain are very high.

Portions of the mid-Atlantic have experienced their share of flooding this summer season.

Most recently, Pittsburgh was the site of a deadly flash flooding incident, with part of southern New Jersey and the New York City Metropolitan area hit with destructive flooding about a week earlier.

Earlier in the summer season, part of Plymouth, Pa. was hit by a wall of water cascading down a hillside.

Motorists are urged to avoid driving through flooded roadways.

In addition to the threat of water levels rising as you attempt to drive through, the road may have been compromised from beneath.

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