This Day in History: Philadelphia Rainfall Leaps Into The Record Books

The summer and fall season bring the Keystone State most of its yearly precipitation with spring being the second wettest time of the year in Pennsylvania. Summer, fall and spring also bring extreme precipitation events such as the one that unfolded 7 years ago today.

 

Frontal systems that push towards the East Coast in the summer tend to slow or come to a screeching halt. This is due to a large high-pressure, known as a Bermuda High, that traditionally becomes anchored off the East Coast in July and August. It is responsible for pumping warm, humid air up the East Coast. 

 

While a fall or winter cold front tends to bring one round of precipitation, summer fronts that stall out bring repeated showers and thunderstorms that contain torrential rain. This is a perfect recipe for major flash flooding to develop within a short period of time. July 28, 2013 was no exception to the rule in eastern Pennsylvania.

 

The surface map on that day shows a north-to-south oriented cold front easing across Pennsylvania. The front was just enough of a catalyst to trigger showers and thunderstorms. Unfortunately, since it slowed down on its approach to the Interstate 95 corridor, multiple waves of torrential downpours triggered flash flooding in Philadelphia that afternoon. 

 

A whirl of problems quickly developed in Philadelphia as the flooding commenced. Interstate 95 ramps around Broad Street closed. One of the terminals at the Philadelphia Airport lost power, 17 flights were cancelled and departure and arrival delays reached 90 minutes. Fortunately, there was only one fatality. A woman drowned after driving into the Schuylkill River near Boathouse Road in downtown. 

 

The official reporting station at the Philadelphia Airport tallied 8.02 inches, which set the all-time calendar day record for the state! The rain pushed July 2013 to a new monthly record of 13.24 inches in Philadelphia that followed a record-breaking 10.56 inches in June. In the first two months of summer, Philadelphia had double the average summer rainfall of 11.28 inches. All told, Philadelphia ended the season with 29.71 inches of rain, which made it the wettest summer since records began here in 1941.

 

The event that unfolded on July 28 fell into the category of a one in thousand-year event, meaning a flooding event of this magnitude has a 0.1 percent chance of happening in any given year. 

 

Philadelphia’s second highest all-time rain total occurred September 16, 1999 when Hurricane Floyd produced widespread flooding across the Keystone State. The Philadelphia International Airport was soaked with 6.63 inches. Six people died and four people drowned in flood waters in Pennsylvania and damage was estimated at $60-million. Almost half-million homes and businesses lost power in southeast Pennsylvania’s PECO Service Territory, the second worst outage in the utility’s history. 

 

Rounding out the top five all-time single day rainfall events in Philadelphia shows they occurred in the summer or fall:

Not to be outdone, Tropical Storm Fay’s rain earlier this month went into Philadelphia’s record books. The 4.15 inches of rain that fell in Philadelphia on July 10, 2020, ranked seventeenth on the list of single day rainfall totals.

 

As summer spills into fall and the height of the tropical season, it’s important to remember that flash flooding is the number one weather-related killer in the U.S. Six inches of fast-moving water can knock you down and two feet of moving water will float a car. The motto “Turn Around, Don’t Drown” when approaching a flooded road could be a life-saver. Try to find an alternative route to your destination when coming across a flooded roadway. 
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Story Image: A map showing accumulated rainfall across Pennsylvania in July 2013. (Courtesy of NOAA)