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i <br />' 4.5.1. Cloud seedability parameter estimated from model 'simulations <br />C <br />7 <br />L <br />F <br />L <br />Values in table 4.3 use an enhancement factor of 0.1 125 that estimates the percentage increase from <br />cloud seeding. This value is based on the product of the two factors, 0.45 and 0.25. The first factor <br />represents the concept that on average, 45 percent of the precipitation (above 9000 feet as used here) in <br />the Headwaters Region is seedable. The 0.25 factor represents that the expected average increase in <br />treated clouds is about 25 percent. The 25 percent increase value is obtained from consideration of the <br />results of the Bridger Range Experiment (Super, 1974; Super and Heimbach, Jr., 1983) and the Climax I <br />and II Experiments (Mielke et al., 1971; 1981). <br />The 0.45 factor was calculated as the average of 7 ratios of precipitation obtained from simulations by <br />Colorado State University with the RAMS model, on 7 storms of the 1998 -99 winter in the Park Range. <br />The precipitation ratios were defined as model total precipitation (using hourly readings from the model) <br />with liquid water present, to model total storm precipitation. The storm seedability ratios do not consider <br />information when seeding leads to precipitation when none would occur naturally. Use of a different <br />ratio was considered that consisted of storm time with liquid water present, to total storm time. However, <br />values appeared unrealistically large and the more conservative ratio was selected. The model did <br />indicate for some periods, lower or no liquid water amounts when the (model) precipitation rate was <br />relatively high. Storms simulated were selected for varying storm types according to time of winter; <br />small, moderate and high actual precipitation amounts, and predominant westerly and nonwesterly wind <br />cases. Three storms were simulated at 3 kilometer grid point resolution and the remainder at 12 kilometer <br />grid spacing. Model simulations appeared to overestimate precipitation (suitable comparisons could not <br />be made because model point estimates at field gauge locations were not available). Simulations need to <br />be compared with actual field observations. Generally, the 3 kilometer simulations yield substantial <br />detail for comparisons. The simulations appear to produce useful information for purposes of the <br />proposed program. These limited model results suggest that additional modeling be pursued should the <br />program move forward. <br />29 <br />