The Redbank Creek Flash Flood of 19 July 1996

Disastrous flash flooding occurred across six counties of Western Pennsylvania on 19 July 1996. Record flooding occurred at the St. Charles, PA river forecast point on the Redbank Creek (watershed area of 1368 km2) as a result of the widespread flash flooding. The synoptic system responsible for focusing the heavy rainfall had produced record flash flooding in Chicago, IL the previous night. Flash floods are most commonly associated with slow-moving thunderstorms. However, the heavy rainfall that resulted in the Redbank Creek flooding was caused by a large number of thunderstorms with cells speeds around 50 knots. The combination of numerous thunderstorms "training" over the same geographic area at high cell speeds resulted in widespread flash flooding and record river flooding.

The Areal Mean Basin Estimated Rainfall (AMBER) program will be used to examine the temporal and spatial distribution of heavy rainfall that produced the flash flooding. The Average Basin Rainfall (ABR) computed by AMBER will be compared with Flash Flood Guidance (FFG) to estimate the severity of flash flooding. The AMBER radar rainfall estimates will be compared with the rain gage measurements to determine the accuracy of the radar rainfall. Brookville, PA in Jefferson County received more than 230 mm of rainfall in less than 12 hours. The ABR rate will be shown to be an effective tool for alerting the forecaster to watersheds in danger of flooding before the flooding begins. The AMBER software is to be implemented nationally in the NWS Automated Weather Information and Processing System (AWIPS) in June of 2001.