The average growing season is 159 days, although it has varied from 122 days in 1963 to 192 days in 1946. May 4th is the average date of the last spring frost with the latest spring frost observed May 27, 1915. The average date of the first fall frost is October 10th with the earliest, aside from the unusual July of 1894, occurring September 17, 1959. The greatest monthly total was 10.54 inches in July 1958, and the maximum 24-hour rainfall was 4.73 inches on August 16, 1941. A statistical analysis indicates the return period for such 24-hour rain in this area is approximately 25 years.
Thunderstorms are primarily warm-season phenomena, but have been observed also in the winter months.
Hurricane winds do not affect the area, however, the storms sometimes have given locally heavy rains. Some damages due to wind and hail associated with severe thunderstorms are usually recorded somewhere in Clinton County each year. Since 1854 when records were first kept on tornadoes, only two such storms have been sighted in Clinton County. Damages in each case were relatively small and no deaths or injuries resulted. Thus Lock Haven appears to be situated in a portion of Pennsylvania least susceptible to severe storms.