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<br />7 . EVALUATION OF THE NORTHERN PORTION OF THE UPPER SNAKE <br /> <br />Target Area <br /> <br />The upper Snake project actually had two target areas. One is immediately north and east <br />of the Bear target area, or just downwind from the Bear target for many storms. The other <br />upper Snake target is the region of Idaho immediately west of Yellowstone Park and <br />bordering Montana. The latter area, to be referred to as the "northem upper Snake" target, <br />will be considered first. Both regions and the Bear target area are shown on figure 8. The <br />target areas specified in the NAWe reports are shown. Unlike the boundary around the <br />drainage area of interest shown on figure 2, these target areas appear to coincide with about <br />the 6500-foot elevation contour. Silver iodide generator locations from NA we maps, and <br />available ses snow measurements sites above 6000 feet, are also shown on figure 8. <br /> <br />Some of the northem upper Snake target and/or control sites could be contaminated by <br />seeding in the Boise project, the rest of the upper Snake project, and in the Bear project for <br />some wind directions. However, AgI concentrations would be quite diluted that far <br />downwind, which would minimize any impact. Several snow measurement sites exist within <br />50 miles east of the Boi.se target which were not chosen for control sites because of concems <br />about seeding affecting them. <br /> <br />7.1 Control Sites <br /> <br />Table 2 lists the target and control snowpack measurement sites used in evaluation of the <br />upper Snake along the Idaho-Montana border. One of the target sites (No. 60) is just <br />downwind from the target, on the Montana side of the barrier crest. However, the site was <br />included because it was judged more likely to be affected by seeding than the lower elevation <br />sites in Idaho. <br /> <br />As in the Boise target analysis, all available target sites and all available upwind controls <br />sites within reasonable distance were used so long as the measurement sites had good April <br />1 SWE records since 1963 or earlier, were above 6000 feet elevation, and were judged <br />unlikely to have serious contamination froni upwind seeding. No attempt was made at this <br />stage to pick a particular set of target or control sites which might make seeding appear <br />either more or less effective than based on analysis of all available sites in a stated category. <br /> <br />The 14 control sites chosen range from west to northwest of the northern upper Snake target, <br />with several control sites in Montana. Two control sites (Darkhorse Lake and Lemhi Ridge) <br />have co-located snow courses and snow pillows. Both types of measurement were used. <br /> <br />19 <br />