The average occurrence of the last temperature of 32 degrees in the spring is late April, and the average first fall minimum of 32 degrees is mid-October. Maximum temperatures during most years are not excessively high and temperatures above 100 degrees are seldom recorded. However, the average humidity in the valley is quite high, and combined with the normal summer temperatures, causes periods of discomfort. Winters in the valley are comparatively mild. Minimum temperatures during December, January, and February are usually below freezing, but below zero temperatures are seldom recorded.
Seasonal snowfall is quite variable.
Freezing rain is a common problem throughout the Lehigh Valley. Snowstorms producing 10 inches or more occur an average of once every two years. The accumulation of snowfall over the drainage area of the Lehigh River to the north of Allentown, combined with spring rains, frequently presents a flood threat to the city and surrounding area. The valley is also subject to torrential rains that cause quick rises in the river and feeder creeks. The area is seldom subject to destructive storms of large extent.