An area of high pressure on the 18th was off the Mid Atlantic coast, while a cold front was well off to the west. In between these two systems was a surface trough, which helped to focus showers and thunderstorms within a warm and humid air mass. The thunderstorms, some severe, marched across the region during the evening hours. The combination of high winds and lightning caused about 27,500 homes and businesses to lose power in Berks County and southeastern Pennsylvania. Power was not fully restored until the 20th.

Thunderstorm Wind in MONTGOMERY, PENNSYLVANIA
From 18-AUG-09 18:56:00 to 18-AUG-09 18:56:00 (EST-5)
Location: SKIPPACK
Magnitude: 51.00 MG
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Trained Spotter

A 59 mph wind gust was measured and penny size hail fell in Skippack Township.

Lightning in DELAWARE, PENNSYLVANIA
From 18-AUG-09 19:05:00 to 18-AUG-09 19:05:00 (EST-5)
Location: LANSDOWNE
Property damage: 10.00K
Crop damage: 0.00K
Reported by: Trained Spotter

A lightning strike and the ensuing fire damaged a home in Lansdowne Borough.

Lightning in BUCKS, PENNSYLVANIA
From 18-AUG-09 19:10:00 to 18-AUG-09 19:10:00 (EST-5)
Location: SILVERDALE
Property damage: 10.00K
Crop damage: 0.00K
Reported by: Trained Spotter

Lightning struck a home in Silverdale Borough and caused a fire. No injuries were reported.

Thunderstorm Wind in BERKS, PENNSYLVANIA
From 18-AUG-09 17:15:00 to 18-AUG-09 17:15:00 (EST-5)
Location: REHRERSBURG
Magnitude: 50.00 EG
Property damage: 0.00K
Crop damage: 0.00K
Reported by: County Official

A severe thunderstorm knocked down a couple of trees in Tulpehocken Township.

Thunderstorm Wind in DELAWARE, PENNSYLVANIA
From 18-AUG-09 18:25:00 to 18-AUG-09 18:25:00 (EST-5)
Location: BOOTHWYN
Magnitude: 50.00 EG
Property damage: 0.00K
Crop damage: 0.00K
Reported by: County Official

A severe thunderstorm tore down large tree limbs in Boothwyn Borough.

Hail in MONTGOMERY, PENNSYLVANIA
From 18-AUG-09 18:56:00 to 18-AUG-09 18:56:00 (EST-5)
Location: SKIPPACK
Magnitude: 0.75 
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Trained Spotter

Thunderstorm Wind in BERKS, PENNSYLVANIA
From 18-AUG-09 18:10:00 to 18-AUG-09 18:16:00 (EST-5)
Location: BOYERTOWN
Magnitude: 56.00 EG
Property damage: 500.00K
Crop damage: 0.00K
Reported by: Newspaper

A severe thunderstorm toppled more than one hundred trees and damaged buildings in Boyertown. A few homes were damaged by downed trees. Two buildings on the 100 block of East Philadelphia Avenue were damaged. There were about twenty weather related calls in the borough. Residents were evacuated from both buildings after bricks were scattered across the alley between them. Both roofs were damaged as well as the exterior wall and chimney of one of the buildings. One building was closed until repairs were made. On another block of East Philadelphia Avenue, a downed tree damaged a roof and a vehicle.  Numerous trees were knocked down on Third Street (making it impassable), Fourth Street and Fifth Street as well within the Boyertown Community Park. At the park, a dugout pavilion rolled over onto its roof and damaged a fence. About 1,300 homes and businesses lost power. Power was not fully restored until the 20th. Property damage in the borough was estimated at $500,000. No injuries were reported.

Thunderstorm Wind in CHESTER, PENNSYLVANIA
From 18-AUG-09 18:00:00 to 18-AUG-09 18:10:00 (EST-5)
Location: BARNSLEY
Magnitude: 52.00 EG
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Trained Spotter

A severe thunderstorm tore down several trees and numerous tree limbs along the southern tier of Chester County in East Nottingham. Elk and Franklin Townships. In Elk Township, downed trees tore down a half a mile power lines on Strickersville Road. Most of the down tree limbs in Franklin Township were on the south side.

Thunderstorm Wind in MONTGOMERY, PENNSYLVANIA
From 18-AUG-09 18:20:00 to 18-AUG-09 18:20:00 (EST-5)
Location: GILBERTSVILLE
Magnitude: 52.00 EG
Property damage: 10.00K
Crop damage: 0.00K
Reported by: Newspaper

A severe thunderstorm tore down several trees in northwest Montgomery County. In Gilbertsville, one downed tree fell through a home. A tree was down on High Street in Pottstown. Trees were down along Pennsylvania State Routes 73 and 100.  About 5,000 homes and businesses lost power in Pottstown, Lower Pottsgrove, West Pottsgrove and Lower Frederick Townships.