Normal Precipitation in Utah

The precipitation in Utah as shown by about 180 records of 5 to 49 years' length is least in the depressions and greatest on the higher windward slopes of the mountains generally, the amount being about 10 times greater on the higher mountains than on the depressions to windward. The increase with altitude is about 4 inches per thousand feet on the windward or western slopes and about 5.50 inches per thousand feet on the opposite side of the mountain ranges which intercept storm tracks. A slight decrease is shown near the crests, and the increase begins some distance to windward of the mountains. An important nonconformity appears on slopes which are interrupted by important initial barriers, beyond which there is sometimes a decrease and always a change in the rate of increase. The windward sides of intermediate valleys are drier usually than the leeward sides. Secular variations in annual and monthly amounts are shown to be without uniformity or reliability. Decade means for every consecutive 10 years in several groups of stations show variations amounting to from 15 per cent to 19 per cent of the 26-year means. The stability of 26-year and longer means is shown to be within 3 per cent the addition of any 10 years' record changing the mean no more than this amount. Certain supposedly wet or dry cycles are shown to be of opposite value or absent from a number of months and stations, and the January to May precipitation is shown to be comparatively stable and subject to less fluctuation. Types of monthly distribution are presented.