Flash Flooding and Flood in Pennsylvania, March 21 to 23, 2000

A rather innocuous looking low pressure system brought heavy rain and some river and stream flooding into most of Eastern Pennsylvania. The rain began just after midnight on the 21st and fell heavy at times from the late afternoon of the 21st into the early morning of the 22nd. Rain lingered at a lighter intensity throughout the rest of the morning on the 22nd. Storm totals averaged between 2 and 5 inches with the highest totals in Berks, Chester and Delaware Counties. There was a tremendous drop in precipiation amounts across eastern sections of the Poconos, Lehigh Valley and the Philadelphia Metropolitan Area. While the storm totals reached 5 inches in Delaware County, it was only 1.72 inches at the Northeast Philadelphia Airport and only half an inch in New Hope (Bucks County). In the Poconos, 2.86 inches of rain fell in Lehighton (Carbon County) and .08 inches in Long Pond (Monroe County). The heavy rain caused considerable ponding of water in low lying and poor drainage areas and forced some streams to overflow. Stream flooding started during the evening of the 21st and persisted through the evening of the 22nd. Hardest hit were Delaware and Chester Counties. In Delaware County flooding occurred along the Brandywine, Chester, Darby and Ridley Creeks. In Darby Borough, flooding along the Darby Creek forced the evacuation of one home and the inundation of another house. Flooding along the Chester Creek caused road closures in Aston Township. Ridley Creek flooded Ridley Creek State Park in Edgemont Township. Flooding along the Brandywine Creek closed U.S. Route 1 in the Chadds Ford-Birmingham (Chester County) area. Basement flooding was reported in Chester City. Winds were not strong, but the heavy rain apparently loosened the ground enough that trees fell down in Middletown Township, Swarthmore Borough, Upper Providence Township and Yeadon Borough. A woman in Middletown Township was hospitalized with minor injuries after a tree fell on her vehicle. A house was damaged in Swarthmore Borough after a tree fell along its side. Around Noon EST on the 22nd, two men were rescued from the flooding Brandywine Creek near the Brandywine River Museum in Chadds Ford after their canoe capsized and left them clinging to trees. In Chester County water swamped numerous roads.Flooding along the Brandywine Creek led to numerous road closures. Several people were rescued from the tops of their stranded automobiles along the Pocopson and Brandywine Creeks in Pocopson Township. Flood waters from the Brandywine Creek closed Pennsylvania State Route 100 at its intersection with Pennsylvania State Route 52 in Birmingham Township; U.S. Route 1 in the Pennsbury/Chadds Ford (Delaware County) area and Pennsylvania State Route 926 along the borders of Birmingham, Pocopson and Pennsbury Townships. This roadway was not reopened until the evening of the 23rd. Goose Creek in Westtown Township and the Octoraro Creek in Upper Oxford Township also flooded.Elsewhere, flooding occurred along the Perkiomen Creek in Montgomery County. Flooding along the Schuylkill River in Philadelphia forced the closure of Kelly Drive. In Lehigh County, flooding was reported during the early morning of the 22nd along the Little Lehigh River and Cedar Creek.In Philadelphia, the Schuylkill River at the Fairmont Dam crested at 11.04 feet at 930 a.m. EST on the 22nd. The flood stage of 11 feet was reached from 8 a.m. through noon EST on the 22nd. In Montgomery County, the Perkiomen Creek at Graterford reached its 11 foot flood stage at 2 a.m. EST on the 22nd. It crested at 11.8 feet at 6 a.m. EST on the 22nd and was back within bankfull at 930 a.m. EST on the 22nd. In Delaware County, the Chester Creek at Chester City crested at 11.2 feet at 6 a.m. EST on the 22nd. It was above its 8 foot flood stage from 815 p.m. EST on the 21st through noon EST on the 22nd. The Brandywine Creek at Chadds Ford crested at 12.7 feet at noon EST on the 22nd. Flood stage is 9 feet. The creek was above its flood stage from 130 a.m. EST on the 22nd through Midnight EST on the 23rd. In Chester County, the West Branch of the Brandywine Creek at Coatesville crested at 7.65 feet at 4 a.m. EST on the 22nd. The creek was above its estimated flood stage of 7 feet from 1230 a.m. EST through 930 a.m. EST on the 22nd. Farther downstream the West Branch of the Brandywine Creek at Modena crested at 9.4 feet at 430 a.m. EST on the 22nd. Flood stage is 9 feet and the creek was above flood stage from 230 a.m. EST through 6 a.m. EST on the 22nd. The East Branch of the Brandywine Creek at Downingtown crested at 10.8 feet. The creek was above its 7 foot flood stage from 10 p.m. EST on the 21st through 130 p.m. EST on the 22nd. The Valley Creek at Valley Forge crested at 7.7 feet at 5 a.m. EST on the 22nd. Flood stage is estimated at 7 feet.Storm totals included 5.23 inches in Chadds Ford (Delaware County), 4.93 inches in West Chester (Chester County), 4.01 inches in Exton (Chester County), 3.79 inches in Morgantown (Berks County), 3.71 inches in Wynnewood (Montgomery County), 3.63 inches in Crum Creek (Delaware County), 3.58 inches at the Blue Marsh Dam (Berks County), 3.45 inches in Pottstown (Montgomery County), 3.27 inches in Bechtelsville (Berks County), 3.20 inches at the Philadelphia International Airport and King of Prussia (Montgomery County), 3.16 inches in Hamburg (Berks County), 2.86 inches in Lehighton (Carbon County), 2.84 inches in Green Lane (Montgomery County), 2.82 inches in Norristown (Montgomery County), 2.76 inches in Palm (Montgomery County), 2.71 inches at the Franklin Institute within Philadelphia, 2.13 inches in Valley Forge (Chester County), 2.08 inches in Sellersville (Bucks County), 2.06 inches in Honey Brook (Chester County), 1.91 inches in Perkasie (Bucks County), 1.72 inches at Northeast Philadelphia Airport and at the Willow Grove NAS (Montgomery County) and 1.30 inches at the Lehigh Valley International Airport The low pressure system responsible for the heavy rain was located near Savannah, Georgia the morning of the 20th. It moved very slowly northeast and at 7 a.m. EST on the 21st it was located near New Bern, North Carolina. The central pressure of this low was about 1017 millibars, higher than normal sea level pressure. The low slowed even further and was located just off of Parramore Island, Virginia at 7 a.m. EST on the 22nd. Its central pressure remained quite weak, only about 1018 millibars. The low then moved quickly out to sea during the day on the 22nd. Just as, if not more, important was a strong blocking high pressure system that remained over the Canadian Maritimes throguhout this event. It slowed the low pressure system's progress and helped establish a prolong and moist southeast fetch from the Atlantic Ocean throughout this event.