The average seasonal precipitation ranges from less than 20 inches in the extreme southeast corner of the county through 30 and 40 inches over much of the central part of the County. In the mountains of the northwest portion totals increase to more than 70 inches at some points, and in the northeast they increase to more than 80 inches.
Totals vary from season to season. In 1 season out of 10, on the average, the total ranges from near 10 inches in the dry, southeast corner to around 20 to 35 inches in the central area and to 40 to 50 inches in the mountains. At the other extreme, in 1 season out of 10, on the average, the dry corner receives more than 30 inches of moisture, the interior 40-50 inches, and the mountain 100 to 110 inches of rainfall.
Rainfall intensities also vary considerably across the County. The greatest 1-hour rainfall is expected to amount to .50 inch to .80 inch about once every 2 years, increasing to 1.10 inches to 2.00 inches once in 100 years. The maximum 6-hour precipitation may be 2.00 to 3.00 inches as often as once in 2 years, increasing to 3.8 to 6.3 inches with a frequency of once in 100 years. Twenty-four hour totals are 3.00 to 6.00 once in 2 years and build up to 5.70 to 12.60 inches once in 100 years.