Low pressure began to develop just off the coast of the Carolinas early on December 16, and steadily moved up the coast through the 16th and into the 17th. The low steadily, but not rapidly, intensified as it moved north. Plentiful moisture was associated with the low thanks to a Gulf of Mexico connection. In addition, very strong high pressure was centered just north of New England, which helped lock in cold air over the mid-Atlantic. The combination of the moisture-rich low and cold air in place led to a significant winter storm over much of the mid-Atlantic. Heavy snow and sleet fell over the area, with some areas also changing to rain as warmer ocean air surged inland and warmer air moved in aloft. While the central pressure of the storm system was not especially low (around 995 mb) the gradient between the low pressure and the very strong high to the north also led to strong winds in the region, especially near the coast. Combined with high astronomical tides, this also led to some coastal flooding.

Winter Storm in DELAWARE, PENNSYLVANIA
From 16-DEC-20 12:30:00 to 17-DEC-20 06:00:00 (EST-5)
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Trained Spotter

Snowfall amounts of 4 to 7 inches were observed, including a report of 6.8 inches from a trained spotter in Chadds Ford Twp.

Winter Storm in MONROE, PENNSYLVANIA
From 16-DEC-20 13:00:00 to 17-DEC-20 06:00:00 (EST-5)
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Trained Spotter

Heavy snow fell in the county, with amounts of 10 to 15 inches observed. A trained spotter in East Stroudsburg reported 15.0 inches of snow.

Winter Storm in CARBON, PENNSYLVANIA
From 16-DEC-20 12:30:00 to 17-DEC-20 06:00:00 (EST-5)
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Trained Spotter

Heavy snow fell in the county, with amounts of 8 to 14 inches reported. A trained spotter near Christmans reported 13.0 inches of snow.

Winter Storm in NORTHAMPTON, PENNSYLVANIA
From 16-DEC-20 13:30:00 to 17-DEC-20 06:00:00 (EST-5)
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Public

Snowfall amounts of 8 to 12 inches were observed, including a maximum report of 12.1 inches in Nazareth.

Winter Storm in LEHIGH, PENNSYLVANIA
From 16-DEC-20 12:30:00 to 17-DEC-20 06:00:00 (EST-5)
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Public

A heavy snowfall of 8 to 14 inches fell in the county, with amounts of 8 to 14 inches observed. A maximum total of 14.0 inches was reported near Vera Cruz.

Winter Storm in BERKS, PENNSYLVANIA
From 16-DEC-20 12:30:00 to 17-DEC-20 06:00:00 (EST-5)
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Trained Spotter

Snowfall amounts of 6 to 10 inches were observed in the county, including a report of 10.0 inches from a trained spotter in Mertztown.

Winter Storm in UPPER BUCKS, PENNSYLVANIA
From 16-DEC-20 13:00:00 to 17-DEC-20 06:00:00 (EST-5)
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Public

Snowfall amounts of 5 to 8 inches were observed, including a report of 8.4 inches in Sellersville.

Winter Storm in LOWER BUCKS, PENNSYLVANIA
From 16-DEC-20 13:00:00 to 17-DEC-20 06:00:00 (EST-5)
Property damage: 0.00K
Crop damage: 0.00K
Reported by: CoCoRaHS

Snowfall of 5 to 9 inches was reported, including a maximum report of 8.8 inches from a CocoRaHS site near Lower Makefield Twp.

Winter Storm in WESTERN MONTGOMERY, PENNSYLVANIA
From 16-DEC-20 12:30:00 to 17-DEC-20 06:00:00 (EST-5)
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Trained Spotter

Snowfall amounts of 5 to 9 inches were reported, including a maximum total of 9.1 inches reported by a trained spotter near Trappe.

Winter Storm in EASTERN MONTGOMERY, PENNSYLVANIA
From 16-DEC-20 12:30:00 to 17-DEC-20 06:00:00 (EST-5)
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Trained Spotter

Snowfall amounts of 4 to 7 inches were observed, including a report of 6.5 inches from a trained spotter in Plymouth Meeting.

Winter Storm in WESTERN CHESTER, PENNSYLVANIA
From 16-DEC-20 12:30:00 to 17-DEC-20 06:00:00 (EST-5)
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Trained Spotter

Snowfall totals of 6 to 9 inches were observed, with a maximum total of 9.6 inches reported by a trained spotter in Elverson.

Winter Storm in EASTERN CHESTER, PENNSYLVANIA
From 16-DEC-20 12:30:00 to 17-DEC-20 06:00:00 (EST-5)
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Trained Spotter

Snowfall amounts of 5 to 7 inches were observed, including a report of 7.0 inches from a trained spotter near Exton.

Winter Storm in PHILADELPHIA, PENNSYLVANIA
From 16-DEC-20 12:30:00 to 17-DEC-20 06:00:00 (EST-5)
Property damage: 0.00K
Crop damage: 0.00K
Reported by: ASOS

Snowfall amounts of 4 to 7 inches were observed. The official measurement for Philadelphia International Airport was 6.6 inches.