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A summary of the key meteorological stability, moisture and dynamic characteristics of each flash flooding event was prepared. Traditionally, meteorologists investigate the vertical temperature and moisture structure of the atmosphere near the event to identify the stability of the atmosphere and infer cloud structure. The surface to 500mb (-20,OOOft) temperatures and dew points and Precipitable Water Index (PWI) form the traditional database for evaluating storms. The surface dew points and PWI are used in standard Site Specific Probable Maximum Precipitation (PMP) studies for dam sizing and re-habilitation studies, Other important atmospheric factors that have not been incorporated into the PMP methodology are the cloud layer shear, sub-cloud layer and cloud layer wind speed and direction and the depth of the warm layer in the updraft, Each of these factors can be used to evaluate the precipitation efficiency and updraft structure of the heavy rain producing storm clouds. The sub-cloud and cloud layer forcing features provide insight into the processes that maintain the flow of moisture into the storm updraft the volume and duration of storm rainfall. The depth of the storm updraft warmer than OC has been reiated to the occurrence of significant flash flooding storms and the efficiency of the storm updraft at producing heavy rainfall. The key characteristics of storms located east and west of the Colorado Continental Divide that were compared are listed below: . Depth of the cloud updraft warm layer which is warmer than 0 C. This factor is related to the precipitation efficiency of the storm cloud and is used operationally to predict storm rainfall in flash flood program. It may prove to be an important addition to PMP evaluations in the near future. . Precipitable Water Index (PWI) from surface to 500 mb measures the amount of moisture available in the atmosphere to be processed by the storm. Traditional site- specific PMP calculations assume the atmosphere is totally saturated with adjustments for elevation and surface dew points maximized. . 700 mb and 500 mb temperature and dew points and wind fields are directly related to the atmospheric stability influencing the strength of the storm clouds updraft. Additionally these fields are used to identify the presence of cloud layer disturbances capable of influencing storm intensity, duration and organization. These factors have not been added to the PMP equation pending the use of atmospheric models. . Cloud layer wind shear are related to precipitation efficiency of the clouds, and . Surface temperature and dew points that are used in traditional PMP calculations. Storm transposition and maximization for site-specific PMP calculations are very sensitive to surface dew points used in the calculations. Each of these factors was evaluated and then composited for comparison purposes. The next two sections of this paper will describe the events that occurred east and west of the Colorado Continental Divide and the final section will present a direct comparison of the storms. Finally some comments will be made of the relative importance of the findings to site-specific PMP preparation in Colorado and in other areas of the mountainous Western states. 2. Flash flooding events east of the Continental Divide (CD-East storms) The Plurn Creek storm of June 16, 1965, the Big Thompson storm of July 31, 1976 and the Frijole Creek storm of July 3,1981 are prime examples of the flash flooding events of significance that have occurred east of the Continental Divide along and in the foothills/plains interface. These storms have all occurred at elevations above 5,000 feet with direct topographic influences. Table 1 shows a detailed summary of each storm and the atmospheric structure attending it. 2