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I I I I I I I I I I I I I I I I I I I worth of data. In WRC's opinion, either the GEV or the Log Pearson III distribution should be used. but that an "at-site" analysis would better represent the Fort CoIlins area since it does tend to be an extreme rather than an average for that area. Using this distribution may be slightly conservative due to the lack of a longer record, but would still represent the City of Fort Collins better than a regional a1\aly~i~ would. c. RESULTS: The results of this report show that the additional period of record results in an increase for the Log Pearson III and the GEV distributions used by WRC and CSU (Oli Sveinsson) in the estimate of the 2 hour and 24 hour results. The results obtained with using an "at-site" Log Pearson Type III analysis shows an increase of 0.27 inches over the current NOAA Atlas 24 hour data and an increase of 1. 17 inches for the 2 hour data. The results obtained from the analyses provided by CSU show an increase of 0.65 inches over the current NOAA Atlas 24 bour data and an increase of 0.48 inches for the 2 hour data. The differences in the 24 hour results stent mainly from the different data used and the "at-site" versus regional analyses. WRC used 98 years of I day data. The I day results were converted to 24 hour values as stated earlier, for an "at-site" analysis, where as CSU used 50 years of 24 hour data and a regional analysis. The differences in the 2 hour results stem almost solely from the "at-site" versus regional analysis, since the same length of data record was used. Therefore, the decision regarding the use of an "at-site" or a regional analysis becomes critical. As stated above, a regional analysis will provide the distribution with more data points from other nearby locations, but those locations need to be representative of the site in question. It was felt by many members of the committee that the City of Fort Collins appears to be dissimilar front the other gage sites in the region. based on historical data. Fort Collins may be in an area that experiences "preferred storm tracks" and seems to experience more frequent extreme rainfall events in comparison to nearby areas. This observation would support the use of an "at-site" analysis using the data set available for the City of Fort CoIlins. The preliminary results provided by NOAA/NWS based on the L-Moment technique suggests a slight decrease in the 24-hour results, but did not include the I 997 value. A comparison of the 2-hour results is not provided. It may be too early to conclude that the final results to be computed by NOAA will -8-