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<br />The Plum Creek storms were dominated by the occurrence of thunderstorm <br />rainfall which fell over a 6 to 72 hour period. The PMP general storm criteria <br />considers a 72-hour storm period, The Plum Creek noods occurred over a large <br />area of the eastern Colorado plains for a period of 7:2 hours. In general, rainfall <br />did not occur throughout the entire 72 hours over an individual basin but focused <br />on discrete 24 to 48 hour periods at anyone place. Figures 3 and 4 show the 24 <br />hour rainfall on June 16, 1965 and June 17, 1965 respectively, <br /> <br />Note that the rainfall on June 16, 1965 falls along a roughly north-south axis <br />which parallels but largely avoids the Front Range foothills in EI Paso, Douglas <br />and Arapahoe Counties (see Figure 3). This rainfall axis is parallel to the mean <br />cloud layer winds which were blowing from 190 degrees, The heaviest rainfall <br />occurred from Palmer Lake to Larkspur to Cherry Creek Reservoir. Note that <br />pockets of rainfall suggest that stronger storm cells existed along the rainfall <br />axis. The pattern is suggestive of train-echo rainfall effects where cells <br />repeatedly formed off Palmer Ridge and tracked along a meteorologically <br />preferred path. <br /> <br />Contrast the roughly north-south rainfall axis of June 16, 1965 to the rainfall axis <br />of June 17, 1965 which runs roughly southwest to northeast in Figure 4, On this <br />date the rainfall axis runs from Fountain to Calhan to Agate or about 45 degrees <br />to the right of the June 16 rainfall axis. Cloud layer winds on June 17, 1965 were <br />blowing from 210 degrees which shifted the rainfall un June 17'h to the east of <br />the preceding day's rain axis. Again ttle location ami intensity of rainfall cells <br />suggests that train-echo rainfall was producE~d by the thunderstorms repeatedly <br />forming on southern foothills of Pikes Peak's orographic enhancement area, <br /> <br />Please note that the rainfall patterns of June 16, 1965 and June 11', 196!5 did not <br />overlap any basin on both days, Additionally no general rainfall from non- <br />thunderstorm sources was reported on either day. The close proximity of both <br />these daily events provides a strong motivation to include both train echo rainfall <br />effects of PMP to near-PMP storm rainfall and consecutive periods of <br />thunderstorm rainfall in the general storm PMP scenario. <br /> <br />None of the general thunderstorm events was attended by a general rainfall. In <br />order to broaden the scenario to a longer 72 hour period of rainfall, a review of <br />all the general storms in Table 2 provided ~Juidance in providing a quantitative <br />description of attendant general storm rainfall to combine with the thunderstorm <br />rainfall in developing a general PMP storm scenario, <br /> <br />The general storms in Table 2 of the most relevance to extreme precipitation <br />events were the Big Elk Meadow storl11 of May 1969 and the June 1965 1=loods, <br />The Big Elk Meadow storm was an intense, long duration, spring upslope storm <br />with snowfall dominating precipitation at altitudes above 10,000 feet. No <br /> <br />13 <br />