Rainfall figures from World Weather Records, for towns west of the Mississippi in the United States, have been subjected to filter analysis. Four filters have been used, and the rainfall patterns obtained suggest substantial coherence of the data throughout much of the entire area. The results agree well with earlier work of Mitchell, Stockton, and Meko, who have reported a relationship between the incidence of drought in the western United States and the double (ca. 22 year) sunspot cycle. However, an additional correlation with the (ca. 18 year) lunar cycle is also apparent, particularly on the west coast.