Because of the prevailing westerly winds that sweep weather systems eastward from the interior of the continent, the Atlantic Ocean has a relatively small effect on Pennsylvania’s climate. The state has climates that are generally known as humid continental. There are distinct seasonal variations and an abundance of rainfall.
Although average temperatures in the north are cooler than those in the south, altitude is particularly important in accounting for climatic variations. The state’s lowland climatic region changes into the upland climatic region at an elevation of about 300 m (about 1,000 ft).
Lowland Pennsylvania includes the Atlantic Coastal Plain and the low-lying hills of the southeast, the valleys of the Ridge and Valley, and the river valleys converging on Pittsburgh. These areas have comparatively long summers and mild winters, with growing seasons ranging from five to seven months and mean annual temperatures ranging from about 12°C (about 54°F) at Philadelphia to about 10°C (about 50°F) in the central valleys.
Upland Pennsylvania includes the higher ridges of the Ridge and Valley and most of the Allegheny Plateaus. Summers are short and winters are comparatively severe.
The growing season is commonly no more than three to four months long, and the mean annual temperature ranges from about 7° to 9°C (about 44° to 49°F).A third type of climate is prevalent in a small area near Lake Erie. The climate there is influenced by the presence of the lake, which is warmer in winter and cooler in summer than the surrounding land. Consequently, the city of Erie has a growing season almost as long as that of Philadelphia and southeastern Pennsylvania, in sharp contrast to the land between. Summers around Erie are long but relatively cool, with a July mean of 19°C (66°F). Winters are comparatively short and not nearly as severe as those farther inland. Erie’s January mean is -2°C (28°F).
Rainfall averages 1,070 mm (42 in) a year, ranging from about 910 mm (about 36 in) in the southwest to 1,270 mm (50 in) and more at higher elevations in the Allegheny and Pocono mountains. Rainfall is heaviest during spring and summer, when it is most needed for growing crops. Snowfall is fairly heavy throughout much of the Allegheny Plateaus, and snow remains on the ground for most of the winter. "Pennsylvania" © Emmanuel BUCHOT, Encarta, Wikipedia
Photos of European countries to visit
Photos of Asian countries to visit
Photos of America