The arrival of an arctic air mass brought the coldest morning of the month of January for most of Eastern Pennsylvania.  Morning low temperatures were in the single numbers, with some below zero readings in the higher terrain. In addition, gusty northwest winds continued into the morning and lowest hourly wind chill factors reached around 25 degrees below zero over the higher terrain of the Poconos and around 10 degrees below zero elsewhere.
Actual low temperatures included 3 degrees below zero in Mount Pocono (Monroe County), 2 degree above zero at the Lehigh Valley International Airport and Lehighton (Carbon County), 4 degrees above zero in Doylestown (Bucks County) and Pottstown (Montgomery County), 5 degrees above zero in West Chester (Chester County) and Nazareth (Northampton County), 6 degrees above zero in Wallingford (Delaware County) and Reading (Berks County) and 9 degrees above zero at the Philadelphia International Airport.
Lowest hourly wind chill factors included 25 degrees below zero in Mount Pocono (Monroe County), 11 degrees below zero in Doylestown (Bucks County), Allentown (Lehigh County) and Reading (Berks County) and 6 degrees below zero in Philadelphia.
As the arctic high pressure system entered the United States near Montana, its surface pressure was quite high: 1058 millibars at 4 a.m. EST on January 7th. At 7 a.m. EST on the 8th, it weakened to 1041 millibars and was located near Memphis, Tennessee. From there, the high pressure system moved east. This reduced the wind and also brought the region a relatively warmer return flow from the southwest on the night of the 8th.

Extreme Cold/Wind Chill in MONROE, PENNSYLVANIA
From 07-JAN-15 16:00:00 to 08-JAN-15 10:00:00 (EST-5)
Property damage: 0.00K
Crop damage: 0.00K
Reported by: ASOS

Cold/Wind Chill in BERKS, PENNSYLVANIA
From 07-JAN-15 22:00:00 to 08-JAN-15 08:00:00 (EST-5)
Property damage: 0.00K
Crop damage: 0.00K
Reported by: ASOS

Cold/Wind Chill in NORTHAMPTON, PENNSYLVANIA
From 07-JAN-15 22:00:00 to 08-JAN-15 08:00:00 (EST-5)
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Mesonet

Cold/Wind Chill in LEHIGH, PENNSYLVANIA
From 07-JAN-15 22:00:00 to 08-JAN-15 08:00:00 (EST-5)
Property damage: 0.00K
Crop damage: 0.00K
Reported by: ASOS

Cold/Wind Chill in WESTERN CHESTER, PENNSYLVANIA
From 07-JAN-15 22:00:00 to 08-JAN-15 08:00:00 (EST-5)
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Mesonet

Cold/Wind Chill in EASTERN CHESTER, PENNSYLVANIA
From 07-JAN-15 22:00:00 to 08-JAN-15 08:00:00 (EST-5)
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Mesonet

Extreme Cold/Wind Chill in CARBON, PENNSYLVANIA
From 07-JAN-15 16:00:00 to 08-JAN-15 10:00:00 (EST-5)
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Mesonet

Cold/Wind Chill in PHILADELPHIA, PENNSYLVANIA
From 07-JAN-15 22:00:00 to 08-JAN-15 08:00:00 (EST-5)
Property damage: 0.00K
Crop damage: 0.00K
Reported by: ASOS

Cold/Wind Chill in DELAWARE, PENNSYLVANIA
From 07-JAN-15 22:00:00 to 08-JAN-15 08:00:00 (EST-5)
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Mesonet

Cold/Wind Chill in UPPER BUCKS, PENNSYLVANIA
From 07-JAN-15 22:00:00 to 08-JAN-15 08:00:00 (EST-5)
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Mesonet

Cold/Wind Chill in WESTERN MONTGOMERY, PENNSYLVANIA
From 07-JAN-15 22:00:00 to 08-JAN-15 08:00:00 (EST-5)
Property damage: 0.00K
Crop damage: 0.00K
Reported by: ASOS

Cold/Wind Chill in EASTERN MONTGOMERY, PENNSYLVANIA
From 07-JAN-15 22:00:00 to 08-JAN-15 08:00:00 (EST-5)
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Mesonet

Cold/Wind Chill in LOWER BUCKS, PENNSYLVANIA
From 07-JAN-15 22:00:00 to 08-JAN-15 08:00:00 (EST-5)
Property damage: 0.00K
Crop damage: 0.00K
Reported by: ASOS