Sequencein variation of annual precipitationin the Western United States

Precipitation data from 211 weather stations in 17 western states from 1900-1939 were collected. Annual and cumulative deviations from long term averages were calculated. The sum of the cumulative deviations was divided by the sum of the annual deviations to obtain a coefficient which is a measure of the tendency for wet and dry years to occur in sequence. A coefficient equal to one fourth the number of years denotes a regular symmetrical cycle. The results show a tendency toward cycles of dry and wet years in the northern one-third of the western states. The results are suggestive rather than conclusive.