Flash Flood in Pennsylvania, June 16 to 17, 2001

Showers and thunderstorms with torrential downpours caused flash flooding of streams and poor drainage flooding in Delaware County, particularly in the eastern half of the county. Most of the flooding occurred east of a line from Radnor Township south through Media Borough and Ridley Township. In Secane (Upper Darby Township), 4.30 inches of rain fell in 90 minutes between 530 p.m. and 700 p.m. EDT. Many vehicles were trapped in flooded roadways and numerous water rescues occurred. The torrential rains and overflowing streams loosened many trees and caused weaker ones to fall. One downed tree damaged a wall and a fence in Swarthmore Borough. Swarthmore College suffered flood damage when the Little Crum Creek flooded. Water went through the doors of several buildings and flooded the basements. Doppler Radar Storm total estimates ranged between 3 and 5 inches across the eastern part of the county. At nearby Philadelphia International Airport, the storm total was 3.38 inches.The low pressure system that was the remnants of Tropical Storm Allison, was very persistent and slow moving. It moved from northeast North Carolina the afternoon of the 15th to near Norfolk the morning of the 16th to the Virginia Capes during the afternoon of the 16th and just east of Atlantic City during the morning of the 17th. Similar to Hurricane Floyd, a cold front was approaching the region from central Pennsylvania on the 16th. An extremely moist and unstable southeast flow preceded both these features. The slight rise in elevation from the coastal plain to the Piedmont in Southeast Pennsylvania (called the fall line) was enough to enhance the precipitation and drop copious amounts across this area.