The combination of a low pressure system that moved off the Eastern Seaboard and an upper air disturbance that moved across from the Great Lakes, produced snow across the region from the night of the 2nd into the night of the 3rd. Snowfall ranged from two to four inches across much of the Poconos, Lehigh Valley, Berks County and upper parts of Chester, Montgomery and Bucks Counties to four to eight inches around the local Philadelphia area. The heaviest snow fell across eastern Chester, southwestern Montgomery, southern Philadelphia and most of Delaware Counties and occurred during the late evening of the 3rd.
Precipitation started as light snow across the Philadelphia northern suburbs on the evening of the 2nd. Precipitation started as light rain around the immediate Philadelphia area. Precipitation changed to snow or started as snow by dawn on the 3rd across much of eastern Pennsylvania. Steady snow did not begin in Chester and Berks Counties until around Noon EST on the 3rd. The snow increased in intensity during the afternoon of the 3rd, but air temperatures around freezing kept much snow from accumulating on roadways. This changed as the sun was setting during the evening rush. Across the immediate Philadelphia area, the snow was enhanced by an upper air disturbance that made the overall air mass more unstable and capable of snowing at greater rates. The snow was falling at the rate of an inch or two per hour during the late evening. The snow ended from north to south. It ended in the Poconos and Lehigh Valley during the evening of the 3rd and by 3 a.m. EST on the 4th across the rest of Eastern Pennsylvania.
It was described as a stealth snowstorm as most of the heaviest snow occurred when it had the relatively least impact on the area. But, one area that was affected was the nearby Philadelphia region as well as the Philadelphia International Airport. Almost 200 passengers had to spend the night of the 3rd at the airport because of cancelled flights. About 40 flights were cancelled the morning of the 4th. Nearly 100 departing planes had to be de-iced. The runways were briefly closed overnight to be cleared. One of the longer runways was closed again around 10 a.m. EST on the 4th for about half an hour so snow could be removed from the north-south runway. All Philadelphia schools were closed on the 4th. Hundreds of other schools around the local Philadelphia area were also closed or had delayed openings.
Specific snowfall included 8.4 inches at the Philadelphia International Airport, 8.3 inches in Wayne (Delaware County), 7.0 inches in Media (Delaware County) and King of Prussia (Montgomery County), 6.6 inches in Perkasie (Bucks County), 6.5 inches in Swartmore (Delaware County), 6.0 inches in Chesterbrook (Chester County) and Wynnewood (Montgomery County), 5.5 inches at Franklin Institue in Philadelphia and Hatboro (Montgomery County), 5.3 inches in East Nantmeal (Chester County), 4.8 inches in Longswamp (Berks County), 4.5 inches in Furlong (Bucks County) and Emmaus (Lehigh County), 4.0 inches in Valley Forge (Chester County), North Wales (Montgomery County) and Bethlehem (Northampton County), 3.2 inches at the Delaware Water Gap (Monroe County), 3.1 inches at the Lehigh Valley International Airport, 3.0 inches in Levittown (Bucks County) and Hatfield (Montgomery County), 2.7 inches in Forks Township (Northampton County), 2.6 inches in Morgantown (Berks County) and Glenmoore and West Chester (Chester County), 2.5 inches in Tobyhanna (Monroe County), 2.3 inches in Palm (Montgomery County), 1.8 inches in Palmerton (Carbon County) and 1.5 inches in Jim Thorpe (Carbon County).
The low pressure system that contributed to the snow formed on a stalled cold front over the southeastern United States on the 2nd. By 7 a.m. EST on the 3rd, it was located about 200 miles east of the Delmarva Peninsula and at 7 p.m. EST that evening it was approaching Nova Scotia. An inverted trough associated with that low pressure system combined with an upper air disturbance to cause enhanced snow across the region, especially the local Philadelphia area during the evening of the 3rd.

Winter Weather in BERKS, PENNSYLVANIA
From 03-FEB-09 12:00:00 to 04-FEB-09 03:00:00 (EST-5)
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Trained Spotter

Winter Weather in CARBON, PENNSYLVANIA
From 03-FEB-09 08:00:00 to 03-FEB-09 18:00:00 (EST-5)
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Trained Spotter

Winter Weather in MONROE, PENNSYLVANIA
From 03-FEB-09 08:00:00 to 03-FEB-09 18:00:00 (EST-5)
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Trained Spotter

Winter Weather in LEHIGH, PENNSYLVANIA
From 03-FEB-09 04:00:00 to 03-FEB-09 23:00:00 (EST-5)
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Trained Spotter

Winter Weather in NORTHAMPTON, PENNSYLVANIA
From 03-FEB-09 04:00:00 to 03-FEB-09 23:00:00 (EST-5)
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Trained Spotter

Winter Weather in BUCKS, PENNSYLVANIA
From 02-FEB-09 22:00:00 to 04-FEB-09 01:00:00 (EST-5)
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Trained Spotter

Winter Weather in MONTGOMERY, PENNSYLVANIA
From 02-FEB-09 21:00:00 to 04-FEB-09 02:00:00 (EST-5)
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Trained Spotter

Winter Weather in CHESTER, PENNSYLVANIA
From 03-FEB-09 12:00:00 to 04-FEB-09 02:00:00 (EST-5)
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Trained Spotter

Heavy Snow in DELAWARE, PENNSYLVANIA
From 03-FEB-09 02:00:00 to 04-FEB-09 03:00:00 (EST-5)
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Trained Spotter

Heavy Snow in PHILADELPHIA, PENNSYLVANIA
From 03-FEB-09 02:00:00 to 04-FEB-09 03:00:00 (EST-5)
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Trained Spotter