The arrival of another arctic air mass brought some of the lowest wind chills and temperatures of the winter season to Pennsylvania 20th and 21st and was responsible for three cold related deaths. With respect to wind chill factors, the late evening on the 19th and the first half of the day on the 20th was colder with wind chill factors as low as around 35 degrees below zero in the Poconos and around 20 degrees below zero elsewhere during the morning. Actual low temperatures were around zero, except below zero in the Poconos. On the morning of the 21st, little, if any, wind was present as the arctic high pressure system was nearby. Low temperatures in more rural inland areas were lower, many were below zero. But, because of the lack of wind, wind chill factors nearly matched the air temperatures and it felt relatively warmer on the morning of the 21st.
Code Blue emergencies were declared throughout the Philadelphia Metropolitan area.  Many school districts on the 20th had delayed openings.  In Philadelphia, an 80 year-old woman who also suffered from dementia and lived in the West Philadelphia section died from hypothermia. A second elderly woman from Philadelphia also died from hypothermia. In Lehigh County, an 86-year-old man with several other medical issues also died from hypothermia.
The arctic air mass also caused school delayed openings as well as burst water pipes and mains. On the 21st, in Philadelphia, about 500 people were displaced from the Rittenhouse Claridge Apartments by a power outage that was caused by a broken sprinkler pipe in a vacant next door store. A water main break in Port Richmond forced dozens of families from their homes.

Lowest hourly wind chill factors included 34 degrees below zero in Mount Pocono (Monroe County), 23 degrees below zero in Doylestown (Bucks County), 22 degrees below zero in Coatesville (Chester County) and Reading (Berks County), 21 degrees below zero in Pottstown (Montgomery County) and the Lehigh Valley International Airport and 17 degrees below zero at the Philadelphia International Airport.
Actual lowest temperatures on either the 20th or 21st included 11 degrees below zero in East Stroudsburg (Monroe County), 10 degree below zero in Mount Pocono (Monroe County), 3 degrees below zero at the Lehigh Valley International Airport, 2 degrees below zero in Reading (Berks County), Perkasie (Bucks County) and Nazareth (Northampton County), 1 degree below zero in Pottstown (Montgomery County) and Spring City and West Chester in Chester County, zero in Swathmore (Delaware County), 1 degree above zero in Bala Cynwyd (Montgomery County) and Langhorne (Bucks County) and 2 degrees above zero at the the Philadelphia International Airport.
The low temperatures of 2 degrees on the 20th and the 16th in Philadelphia were the coldest winter days in the city since January 20, 1994 (the low as 1 degree above zero) and the coldest February lows since February 20, 1979. The low temperature of 3 degrees below zero at the Lehigh Valley International Airport on the 21st broke the daily record set in 1936 and the low temperature of 10 degrees below zero in Mount Pocono on the 21st broke the daily record set in 1993.
The latest cold outbreak was caused by an arctic high pressure system that arrived in Eastern Pennsylvania late in the afternoon on the 20th. The wind and subsequent low wind chill values was caused by the pressure difference between the approaching high pressure system and an intensifying low pressure system that moved through the Canadian Maritimes overnight on the 19th and on the 20th. While some low temperatures were lower on the morning of the 21st, there was little if any wind and the air and wind chill values that morning were one in the same.  As the high pressure system moved offshore, more wintry precipitation arrived later in the day on the 21st.

Extreme Cold/Wind Chill in MONROE, PENNSYLVANIA
From 19-FEB-15 22:00:00 to 20-FEB-15 10:00:00 (EST-5)
Property damage: 0.00K
Crop damage: 0.00K
Reported by: ASOS

Extreme Cold/Wind Chill in CARBON, PENNSYLVANIA
From 19-FEB-15 22:00:00 to 20-FEB-15 10:00:00 (EST-5)
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Mesonet

Cold/Wind Chill in BERKS, PENNSYLVANIA
From 19-FEB-15 22:00:00 to 20-FEB-15 10:00:00 (EST-5)
Property damage: 0.00K
Crop damage: 0.00K
Reported by: ASOS

Cold/Wind Chill in WESTERN MONTGOMERY, PENNSYLVANIA
From 19-FEB-15 22:00:00 to 20-FEB-15 11:00:00 (EST-5)
Property damage: 0.00K
Crop damage: 0.00K
Reported by: ASOS

Cold/Wind Chill in LOWER BUCKS, PENNSYLVANIA
From 19-FEB-15 22:00:00 to 20-FEB-15 11:00:00 (EST-5)
Property damage: 0.00K
Crop damage: 0.00K
Reported by: ASOS

Cold/Wind Chill in LEHIGH, PENNSYLVANIA
From 20-FEB-15 00:00:00 to 20-FEB-15 11:00:00 (EST-5)
Property damage: 0.00K
Crop damage: 0.00K
Reported by: ASOS

Cold/Wind Chill in PHILADELPHIA, PENNSYLVANIA
From 20-FEB-15 00:00:00 to 20-FEB-15 10:00:00 (EST-5)
Property damage: 250.00K
Crop damage: 0.00K
Reported by: ASOS

Cold/Wind Chill in UPPER BUCKS, PENNSYLVANIA
From 19-FEB-15 22:00:00 to 20-FEB-15 11:00:00 (EST-5)
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Mesonet

Cold/Wind Chill in EASTERN MONTGOMERY, PENNSYLVANIA
From 19-FEB-15 23:00:00 to 20-FEB-15 10:00:00 (EST-5)
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Mesonet

Cold/Wind Chill in EASTERN CHESTER, PENNSYLVANIA
From 19-FEB-15 23:00:00 to 20-FEB-15 10:00:00 (EST-5)
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Mesonet

Cold/Wind Chill in WESTERN CHESTER, PENNSYLVANIA
From 19-FEB-15 21:00:00 to 20-FEB-15 11:00:00 (EST-5)
Property damage: 0.00K
Crop damage: 0.00K
Reported by: AWOS

Cold/Wind Chill in DELAWARE, PENNSYLVANIA
From 20-FEB-15 00:00:00 to 20-FEB-15 10:00:00 (EST-5)
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Mesonet

Cold/Wind Chill in NORTHAMPTON, PENNSYLVANIA
From 20-FEB-15 00:00:00 to 20-FEB-15 11:00:00 (EST-5)
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Mesonet