A potent low pressure system in the Ohio Valley during the early morning hours of May 11th moved eastward and gradually weakened. A secondary low formed over northeastern North Carolina during the late afternoon on the 11th and eventually absorbed the other low pressure system, becoming the dominant storm. This storm gradually moved east northeastward late on the 11th into the 12th. Early on the morning of the 12th, the storm was centered over the southern Delmarva. As this storm strengthened fairly rapidly, a gusty northeast wind developed and persisted through a portion of the 12th. The prolonged northeast flow combined with higher than normal tides, which caused some minor tidal flooding in Southeastern Pennsylvania along the Delaware River. There was limited moisture inland from the center of the storm. By the evening of the 12th, the coastal storm tracked eastward and gradually moved away from the region.
Due to the high winds on the 12th, tractor-trailers were temporarily banned from the Commodore Barry Bridge between Chester, Pennsylvania and Bridgeport, New Jersey. Trees were reported down across Delaware County, including Franklin Avenue in Ridley Township and Chestnut Street in Collingdale. In Aston (Delaware County), an 85-foot tree was reportedly knocked down on Gordonville Road, which blocked six properties. A huge tree limb fell onto a vehicle in Hinckley Avenue in Ridley Park and on a vehicle in the parking lot of Woodstream Condominiums on South Avenue in Ridley Township.
The Federal Aviation Administration reported that arrival flights at the Philadelphia International Airport were delayed on the 12th on average of three hours because of wind and rain. More than 130 flights were either cancelled or delayed on the 12th because of the storm.
Peco Energy reported about 50,000 customers lost power during the Nor���easter on the 12th, with most of the outages in Chester and Delaware Counties, however some outages were also reported in Montgomery County. The cause was wind gusts to around 45 mph, which brought tree limbs down onto electrical lines. By 5:00 PM EDT on the 12th, all but 6,000 customers had their service restored.
Strong winds coupled with heavy rain knocked down a large tree at Church Street and Oakland Avenue in Doylestown (Bucks County) on the 12th. Strong winds and rainfall caused a tree to fall on the 12th in Bryn Mawr (Montgomery County), which landed on a car and crushed its roof at around 10:00 AM EDT. The driver of the vehicle was not seriously injured. In Franconia (Montgomery County), a tree with exposed roots leaned on a swing set in a backyard during the morning of the 12th, as gusty winds and a wet ground were too much for it. In Whitpain (Montgomery County), downed trees closed three roads during the morning of the 12th. At 5:23 AM EDT, police responded to a fallen tree on School Road, which was closed between Route 73 and Boehms Church Road. Morris Road was shut down between Mt. Pleasant Avenue and Betsy Lane for more than four hours. Around 11:00 AM EDT on the 12th, Stenton Road was closed near the intersection of Norristown Road while a Pennsylvania Department of Transportation crew removed a fallen tree. In Skippack (Montgomery County), state troppers closed a portion of Hutnut Road, near the intersection of Skippack Pike, after a downed tree caused a power outage.
The tide gage at Philadephia peaked at 8.9 feet mean lower low water at 8:00 AM EDT on the 12th. Minor tidal flooding begins at 8.2 feet mean lower low water, and moderate tidal flooding begins at 9.2 feet mean lower low water. Some peak wind gusts included: 49 mph at the Philadelphia International Airport; and 47 mph at the Northeast Philadelphia Airport.

Strong Wind in PHILADELPHIA, PENNSYLVANIA
From 12-MAY-08 07:15:00 to 12-MAY-08 08:15:00 (EST-5)
Magnitude: 43.00 MG
Property damage: 10.00K
Crop damage: 0.00K
Reported by: Official NWS Observations

A peak wind gust of 49 mph was measured at the Philadelphia International Airport during the morning of the 12th. In addition, a peak wind gust of 47 mph was measured at the Northeast Philadelphia Airport. These gusts occurred generally between 8:15 AM EDT and 8:45 AM EDT on the 12th.

Strong Wind in DELAWARE, PENNSYLVANIA
From 12-MAY-08 07:15:00 to 12-MAY-08 08:15:00 (EST-5)
Magnitude: 43.00 MG
Property damage: 10.00K
Crop damage: 0.00K
Reported by: Official NWS Observations

A peak wind gust of 49 mph was measured at the Philadelphia International Airport during the morning of the 12th. This peak gust occurred generally between 8:15 AM EDT and 8:45 AM EDT on the 12th.

Strong Wind in MONTGOMERY, PENNSYLVANIA
From 12-MAY-08 09:00:00 to 12-MAY-08 09:00:00 (EST-5)
Magnitude: 40.00 EG
Property damage: 5.00K
Crop damage: 0.00K
Reported by: Broadcast Media

The combination of strong winds and rainfall caused a tree to fall on the 12th in Bryn Mawr (Montgomery County), which landed on a car and crushed its roof at around 10:00 AM EDT. The driver of the vehicle was not seriously injured.