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<br />. <br />. <br />. <br />. <br />. <br />. <br />. <br />. <br />. <br />. <br />. <br />. <br />. <br />. <br />. <br />. <br />. <br />. <br />. <br />. <br />t <br />t <br />. <br />. <br />t <br />. <br />t <br />. <br />. <br />. <br />. <br />. <br />. <br />. <br />t <br />. <br />. <br />t <br />. <br />. <br />. <br />. <br />. <br /> <br />There is one other consideration in the selection of control sites. pOlential downwind <br />effects of other cloud seeding projects beyond the intended target areas. Some earlier weather <br />modification research programs have indicated that the precipitation can be modified in areas <br />downwind of the intended target areas. Analyses of some of these programs have indicated <br />increases in precipitation in these downwind areas out to distances of 50-100 miles. N"A we <br />recently completed an analysis of the potential downwind effects of cloud seeding. utilizing a <br />long-tenn program that has been conducted in central and southern Utah (Solak. et a1. 2003). <br />Historical regression equations ""ere developed for that study to examine the possible existence <br />of dowO\I.:ind effects. Figure 4.2 taken from that study shows the actual over predicted <br />precipitation ratios for several sites in southeast Utah and southwest Colorado. This figure <br />(4.2) indicates possible positive dow-nwind effects from this program out to locations near the <br />Utah-'Colorado border. a distance of approximately 100 miles from the location of the seeding <br />generator network. The downwind study therefore suggests that if \ve wish to consider any <br />precipitation gage sites in eastern Utah as control sites for the Gunnison project. they should be <br />only those near the eastern border of the state. Otherwise. we might use sites that have been <br />contaminated by the seeding in central and southern Utah. There is also more general guidance <br />provided by this study: areas up to approximately <br /> <br /> <br />Fi~ure ~.2 Actual/Predicted down"ind ratios from Utah stud~' <br /> <br />33 <br />