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Philadelphia torrent: City has rainiest day on record Sunday

From Hazel to Floyd to Sandy, the City of Brotherly Love has endured some great storms. Yet somehow, a rather modest mid-summer front managed to put down over 8 inches of rain in Philadelphia Sunday, giving the city its greatest daily deluge in over 140 years of weather records.

The 8.02 inches of rain that fell easily exceeded the previous single day record in Philadelphia of 6.63 inches from September 16, 1999 during hurricane Floyd.  The whopping total pushed its July rainfall over 13 inches, making it the wettest July on record by a healthy margin. The previous July record was the 10.42 inches that rained down in 1994.

Incredibly, 7.35 inches of the Sunday’s 8.02 inches fell in 4.5 hours (source @WxNick on Twitter) !

The rain can be blamed on a strong push of moist tropical air ahead of a slow-moving cold front (and a strong jet stream at high altitudes). In this humid, unstable air, strong thunderstorms developed in long, train-like formations, oriented from southwest to northeast. The storms then tracked over the same locations with unrelenting downpours.

Unlike a tropical storm, whose heavy rain often leaves a massive footprint, Sunday’s heavy rains were very localized, falling in a fairly narrow ribbon from Philadelphia into some of its eastern suburbs in southwest New Jersey.

“South Jersey, the southeastern half of Philadelphia, and down into Wilmington were the “winners” in the rainfall game as training set up shop and ran over the same real estate,” explains the blog

Doppler radar estimated rainfall in the region around Philadelphia Sunday. Note: these amounts are likely underestimates in some locations. (National Weather Service)

Consider, also, Baltimore and Washington received just a trace of rain, and New York city logged less than a quarter inch.

The rain in Philadelphia and its eastern suburbs caused street flooding and, at Philadelphia International Airport, all American Airlines flights are cancelled through at least noon today due to power problems caused by the rain.

Here are a few images of the flooding, from Twitter:

Jason is the Washington Post’s weather editor and Capital Weather Gang's chief meteorologist. He earned a master's degree in atmospheric science, and spent 10 years as a climate change science analyst for the U.S. government. He holds the Digital Seal of Approval from the National Weather Association.
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Jason Samenow · July 29, 2013

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