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t PRECIPITATION RECORDS AND FLOOD-PRODUCING STORMS IN CHEYENNE. WYOMING By J. B. Lindner-Lunsford ABSTRACT Annual maximum precipitation data for Cheyenne, Wyoming are presented for ,the years 1902-86 for durations of 5, 10, 15, and 30 minutes, and 1 and 2 hours. Annual maximum precipitation data for 24-hour duration, are presented for the years 1871-1986. Precipitation-frequency curves are developed using only data collected before 1985. A second set ofprecipita- tion frequency curves are developed based on data collected from 1871 through 1986 (including the storm of August 1, 1985), The data are plotted and analyzed in three ways, assuming: (1) The data are described by an arithmetic Gumbel distribution, (2) the logarithms of the data are described by a Gumbel distribution, and (3) the logarithms of the data are described by a Pearson Type III distribution. The inclusion of data for the large storm of August 1, 1985, had the most noticeable effect on the prediction of the magnitude of storms of long recurrence interval for the 1- and 2-hour durations. Four different methods of analysis were used to develop seven intensity-duration curves for the 100-year storm. These curves were compared to the observed curve for the August 1, 1985, storm. For durations greater than 30 minutes, the observed curve indicates greater intensity than do five of the seven calculated curves. Dimensionless hyetographs were developed for 10 flood-producing storms that have occurred in the Cheyenne area since 1903. Pattern index (integral of the dimensionless hyetograph curve) was calculated for each storm. The index for the storm of August 1, 1985, is three standard deviations less than the mean of the pattern indices calculated for the remaining nine storms--indicating that the distribution of precipitation over time for the August 1 storm was outside the normal range for Cheyenne. 1