An analysis of the monthly sequence of rainfall during the summer period April-September of the years 1890–1937, made by expressing each annual sequence as a fifth-degree polynomial function of time, indicates that despite marked annual variability the average monthly precipitation at all three stations exhibits a definite seasonal trend, with the maximum incidence of rain in June or July. At Winnipeg, the relative monthly distribution remains, on the average, essentially the same in both wet and dry years, but at Swift Current and Edmonton it is modified to some extent, the midseason maximum being relatively more pronounced in seasons of above-average total precipitation. At Swift Current, both the total amount and one of the coefficients specifying the monthly distribution of precipitation show some oscillatory variation with time; and at Edmonton, there has been a slight progressive change such that a smaller proportion than formerly of the total precipitation now falls in the second half of the season (July-September). No consistent increase or decrease in rainfall over the 48-year period has been recorded at any of the three stations.