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East Slope Storms <br />The historic storms of this type considered in the Williams Fork study are still the <br />largest in the historical record. These storms produce their heaviest rainfall east of the <br />Continental Divide with lesser amounts over regions immediately to the west of the Divide. <br />These storms turned out to be insignificant for the Williams Fork basin. Since the rainfall <br />produced by these storms is confined to the eastern portion of the Williams Fork basin, they are <br />even less significant for the Henderson Mill drainage basin. The most significant storm of this <br />type is the transpositioned Glacier Park storm. The transpositioned and maximized isoheytal <br />pattern is presented in Figure 6. Very small rainfall amounts extend westward over the <br />Continental Divide with insignificant amounts over the Henderson Mill drainage. Hence this type <br />of storm is not considered to be capable of producing a PMP event at the Henderson Mill <br />location. <br />Moist Southwest Flow Events <br />This storm has the greatest opportunity to produce large rainfall over basins in the <br />high Rockies because of the availability of significant amounts of moisture being brought in from <br />the Pacific Ocean to the southwest. The storms evaluated in the Williams Fork are still the largest <br />in the historical record. These storms of this type which produce large rainfall totals occur to the <br />southwest of our area of interest. Any well organized moist flow with a strong southerly <br />component encounters major mountain barriers as it intrudes into the southwest. The largest of <br />these events were maximized and transpositioned over the Williams Fork basin. The isohyetal <br />patterns from these storms have been influenced by the upwind barrier effects of the Gore and <br />William Fork Ranges. The storm centering was matched as closely as possible the relationship of <br />the rainfall center with the topography. The most significant maximized and transpositioned <br />isoheytal pattern resulted from Bug Point center of the September1970 storm. The isoheytal <br />pattern is presented in Figure 7. <br />Page 13 <br />