One of the distinguishing features of such a climate is a moderately wide seasonal temperature range, and precipitation is distributed in a definite pattern. Summers are generally pleasant with warm days, cool nights, a high proportion of sunshine and occasionally an afternoon or evening thunderstorm. Occasionally, warm, humid, tropical air from the Gulf of Mexico reaches as far north as Pennsylvania causing a heat wave that may persist several days. Although daytime temperatures may sometimes be hot, nights are generally comfortable due to cool air draining off the nearby higher elevations. In clear weasther, of which there is much in summer, this effect is most pronounced.
Winters are usually cold with extended periods of cloudiness and precipitation.
During the months of December, January and February temperatures average near the freezing mark with daily minima frequently dipping into the 20's and teens. Low readings of zero or below occur on the average of 3 days per year and can be expected during 2 out of 3 winter seasons. Not all temperatures during the winter are on the cold side, however. Spring and fall are, of course, the transition periods from cold to warm weather, and vice versa. Freezing temperatures have been reported as late as May 30th and as early as September 30th.