The climate of Pennsylvania is diverse due to the multitude of geographic features found within the state. Straddling two major climate zones, the southeastern corner of Pennsylvania has the warmest climate. A portion of Greater Philadelphia lies at the southernmost tip of the humid continental climate zone, with the city proper being in the humid subtropical climate zone. Still, Philadelphia features colder, snowier winters than most locations with a humid subtropical climate. Moving west toward the mountainous interior of the state, the climate becomes markedly colder, the number of cloudy days increases,The Pennsylvania State Climatologist. Annual Average Number of Cloudy Days In Pennsylvania. Retrieved on 2008-01-28. and winter snowfall amounts are greater.
Using the January freezing isotherm, the humid subtropical climate (Cfa) only exists in parts of Greater Philadelphia and low-lying areas of the lower Susquehanna Valley from Harrisburg downriver. Pennsylvania's hardiness zone ranges from 5a in high-elevation areas to 7b in parts of Delaware and Philadelphia Counties.
Precipitation Western areas of the state, particularly cities near Lake Erie, can receive over of snowfall annually, and the entire state receives an average of of rainfall every year. Floods are more common in March and April than other months of the year.The Pennsylvania State Climatologist. Climate of Pennsylvania. Retrieved on 2008-01-28.
Tropical cyclones Tropical cyclones normally threaten the states during the summer and fall, with their main impact being rainfall. Although Hurricane Agnes was barely a hurricane at landfall in Florida, its major impact was over the Mid-Atlantic region, where Agnes combined with a non-tropical low to produce widespread rains of to with local amounts up to in western Schuylkill County in Pennsylvania. These rains produced widespread severe flooding from Virginia northward to New York, with other flooding occurring over the western portions of the Carolinas.
Philadelphia has received sustained winds approaching hurricane-force from tropical cyclones in the past.David M. Roth and Hugh D. Cobb III. RE-ANALYSIS OF THE GALE OF '78 - STORM 9 OF THE 1878 HURRICANE SEASON. Retrieved on 2008-03-05.
Climate extremes Temperature The state record low is , recorded at Smethport on January 5, 1904, while the state record high is , recorded at Phoenixville on July 9 and 10, 1936.
Precipitation Rain Event Measurement Date LocationGreatest 24-Hour Rainfall June 22, 1972 (during Hurricane Agnes) York
Note: While the official measured rainfall record is given above, the NCDC notes that an estimated of rain fell in 12 hours near Smethport on July 17, 1942. The NCDC says this is "arguably the greatest 24-hour rainfall on record outside of the tropics".
Snow Event Measurement Date Location Greatest 24-hour snowfall March 20, 1958 Morgantown Greatest two-day snowfall December 24–26, 2017 ErieGreatest snow depth March 22 & 23, 1958 Gouldsboro
Hurricanes Event Measurement Date Location Wettest Tropical Cyclone Agnes (1972) Western Schuylkill County
Climate statistics for selected cities
See also Johnstown Flood Wind power in Pennsylvania
Notes
References