Flash Flooding in Pennsylvania, December 17 to 18, 2000

An unseasonably warm air mass and an intense low pressure system and cold front not only set the stage for an extremely windy day, but also produced heavy rain and flooding across Southeast Pennsylvania. A series of showers and thunderstorms with heavy downpours moved across the region during the first half of the 17th. The heaviest rain fell just on the Chester County side of the Chester/Delaware County line northeast through central Montgomery County into northern Bucks County. Doppler Radar storm total estimates exceeded four inches in isolated locations in Upper Bucks County. The heavy rain caused urban and poor drainage flooding and also led to the flooding of some major streams and rivers in the region.In Bucks County, the upper part of the county was hit hard by flooding. In the Pennridge area 2.5 inches of rain fell between 630 a.m. and 730 a.m. EST alone. Streams in the area including the East Branch of the Perkiomen Creek flooded. Roads, basements and parkland were flooded. In Sellersville, a half dozen homes had their basements pumped. Roads were also closed in Perkasie, West and East Rockhill Townships. In West Rockhill Township, a rockslide blocked one roadway. In Chester County, the Brandywine Creek flooded and forced road closures including Pennsylvania State Route 100 in Pocopson Township. The French Creek flooded. Other creek flooding forced road closures in Westtown and East Goshen Townships. In Chester County, the East Branch of the Brandywine Creek below Downingtown reached its 7 foot flood stage at 930 a.m. EST on the 17th, crested at 10.78 feet at 130 p.m. EST and was back within bankfull at 730 p.m. EST on the 17th. Farther downstream, the Brandywine Creek at Chadds Ford (sharing the Delaware County line) exceeded its 9 foot flood stage from 230 p.m. EST on the 17th through 4 a.m. EST on the 18th. It crested at 10.64 feet at 9 p.m. EST on the 17th. In Delaware County, the Chester Creek near Chester was above its 8 foot flood stage from 915 a.m. through 6 p.m. EST on the 17th. It crested at 8.97 feet at Noon EST. In Montgomery County, the Perkiomen Creek at Graterford reached its 11 foot flood stage at 10 a.m. EST on the 17th, crested at 13.71 feet at 5 p.m. EST on the 17th and was back within bankfull at 830 p.m. EST on the 17th. In Bucks County, the Neshaminy Creek at Langhorne reached its 9 foot flood stage at 4 p.m. EST on the 17th, crested at 9.93 feet at 7 p.m. EST on the 17th and was back within bankfull at 10 p.m. EST on the 17th. The Schuylkill River came within one foot of its flood stage at most of its forecast points including Philadelphia.Storm totals included 3.45 inches in West Chester (Chester County), 3.34 inches in Glenmoore (Chester County) and Springtown (Bucks County), 3.25 inches in Exton (Chester County), 3.24 inches in Perkasie (Bucks County), 2.72 inches in Palm (Montgomery County), 2.64 inches in Green Lane (Montgomery County), 2.52 inches in Pottstown (Montgomery County), 1.55 inches at the Willow Grove NAS (Montgomery County) and 1.28 inches in Neshaminy Falls (Bucks County)