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<br />2.2 Enhanced data sets for historic l'Iooriing E!Vents <br /> <br />The rainfall patterns of the storms identified in Tables 1 and 2 are candidates for <br />transposition to the Mason Reservoir drainage basin. Since this basin is less <br />than 10 square miles in area, the peak transposed rainfall for each of these <br />storm events is assumed to be representative of the peak rainfall over the entire <br />basin, This simplifies comparison of maximized and transposed rainfall from <br />different storms. It also opens another opportunity to utilize an enhanced data <br />set which was not available during the development of HMR 55A methodologies, <br />i,e" the use of composite storm atmospheric vertical structur,es or <br />representative storm atmospheres, <br /> <br />HMS compiled detailed atmospheric structure information for all of the shaded <br />events listed in Tables 1 and 2 for the purpose of constructing representative <br />storm atmospheres for use in evaluating the site-specific PMP for the Mason <br />Reservoir basin. The data was obtained from the HMS Storm Archives, the <br />National Climatic Data Center, and the Colorado Climate Center's Colorado <br />Extreme Precipitation Study data base. Electronic file transfers of key upper air <br />and surface data were made and analyses pelformed, <br /> <br />The use of composite storm atmospheres was popularized over the past tvventy <br />years by studies conducted by Dr. Robert Maddox of the Environmental <br />Research Laboratories of NOAA who devoted considerable effort into <br />researching the meteorological causeS offlash flooding in the United States, The <br />composite extreme atmospheres constructed by Maddox et al (19130) while <br />investigating over 50 observed flash floods in the United States, established the <br />value of considering the vertical structure of the atmosphere and related weather <br />features affecting the production of flooding rainfalls. <br /> <br />HMS compiled the vertical temperature, moisture and wind structure for each <br />flooding event in Tables 1 and 2 using stanclard NWS observations. HMS used <br />the program, RAOS Version 3.5, to compute an objective soundin() over the <br />flooded basin from surface and upper air obsel"Vations for the time period of the <br />flooding event. The synthesized storm atmosplleres and associated <br />components are presented in Table 3 for the local and general thunderstorm <br />cases, <br /> <br />9 <br />