Flash Flood — Philadelphia, Pennsylvania

2013-07-28 · near Overbrook, Philadelphia, Pennsylvania

Event narrative

Thunderstorms with very heavy rain caused urban and poor drainage flash flooding in Philadelphia. Multiple ramps of Interstate 95 around Broad Street were closed. A 21-year-old woman drowned after she accidentally drove into the Schuylkill River near Boathouse Road in Philadelphia. A 31-year-old male passenger managed to swim to safety. The river was running higher than average, but was not flooding at the time of the drowning. SEPTA Regional rail lines reported flooding on tracks within Philadelphia. The flooding rains caused portions of Terminal A at Philadelphia International Airport to lose power. Departure and arrival delays reached 90 minutes and seventeen flights were cancelled. Event precipitation totals included 8.26 inches at the Philadelphia International Airport and 1.84 inches in Center City. The precipitation gradient was tremendous over Philadelphia as only 0.64 inches fell at the Northeast Philadelphia Airport.

A total of 8.02 inches of rain fell at the Philadelphia International Airport on the 28th. The amount not only established a new record daily maximum rainfall for that date, but was also the most rainfall on record for any calendar day in Philadelphia. The previous record was set on September 16, 1999 during Tropical Storm Floyd and was 6.63 inches. This torrential downpour also helped establish a new July monthly rainfall record of 13.24 inches in Philadelphia. The previous record was 10.42 inches set in 1994.

Wider weather episode

A slow moving cold front coupled with a deep southerly flow of very moist air caused slow moving and in some instances back building thunderstorms to occur during the afternoon and evening of the 28th. This caused an all-time record breaking rainfall in Philadelphia as well as flash flooding in Philadelphia and Delaware Counties and also in parts of the Poconos and Lehigh Valley. Doppler Radar storm total estimates and or actual measurements reached around 4 inches in parts of the Lehigh Valley, 6 to 8 inches in parts of the Poconos and around 8 inches in parts of the local Philadelphia area. The daily rainfall measurement of 8.02 inches at the Philadelphia International Airport was not only the all-time calendar day record but was estimated to be a one in thousand year event. This event also helped establish back-to-back all-time monthly rainfall records in Philadelphia. The July 2013 precipitation total of 13.24 inches was a new monthly record for Philadelphia and came on the heels of a record breaking 10.56 inches falling in June. The current normal meteorological summer seasonal precipitation average for Philadelphia is 11.28 inches.

View location on OpenStreetMap → (39.9400, -75.2400)

Source: NOAA Storm Events Database, event_id 468025. Narrative written by the NWS forecast office that issued the report.