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decisions on the values of site-specific PMP. The addition of climatic extremes to assist in the establishment of extreme precipitation atmospheric: structul"e is fundamentally sound when used in gtJidinSJ decision making on the use of appropriate PWI values and in making elevation adjustments to potential rainfall rates. The application of the extreme precipitation event atmospheric data and the Convective Storm Methodology has resulted in significant reductions in the site- specific local storm and general storm PMP compared to the values obtained using the HMR 55A Plates. Even with these reductions HMS believes that its PMP values for the Mason Reservoir basin are consl3rvative. 7.0 Opinion on extreme snow melt occurrence during a PMP eve lilt The occurrence of a local or general storm PMP event simultaneously with an extreme snow melt is a valid design concern. The occurrence of an extreme snow melt in Colorado was almost achieved in Colorado during Spring 19S15. A record snow pack was prevalent in most of the mountain basins into mid to late June. In effect, the snow melt was delayed almost a month later than its previous latest peak. During the period from mid-April to mid-July 1995, John Henz of the HMS staff was part of the Colorado Flood Task Force which advised the Govemor and state agencies on the expected oc:currence of the snow melt peak and predicted related river flows, Clear patterns between temperature, precipitation patterns and changes in river runoff were documented during this period by the Task Force. Weekly summaries which related observed weather patterns, precipitation and runoff presented a clear view of the relationship of the runoff to the weather. When temperatures were observed to warm above the freezing mark at elevations above 10,000 feet the river runoff was observed to increase with a 24 hour lag response period. The most dramatic increases in runoff volume were observed during periods of three days or more of above norma I warmth at elevations above 10,000 feet. However, the river runoff was observed to dramatically decrease when the cloud cover and subsequent cooler temperatures associated with precipitation events were obsented. Again the runoff quickly slowed over a 24 hour period. Excessive runoff required at least a 3 to 5 day period of above normal weather to reach peaks but quickly fell below dangerous levels when cloud cover and precipitation events were noted. It is interesting to note that the Task Force was in general consensus that the weather patterns during the runoff period this spring were similar to the ones observed during the 1965 floods. The 1965 June Floods in Colorado were not the result of a record spring snow melt runoff. Rather the fioods were the 44