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<br />" <br /> <br />local terrain. But considerable past experience suggests that locating generators more than 1500- <br />2000 ft below typical crest lines runs the serious risk of targeting failure while stonns are occurring. <br />Operating an economical generator network, with all units accessible from all-weather roads, may <br />be no bargain at all if actual cloud seeding is infrequently accomplished. The tenn "cloud seeding" <br />may be a misnomer in far more winter seeding attempts than is commonly realized. <br /> <br />Detailed wind measurements or tracer studies between the AgI generators used during the <br />2002/03 winter and the large intended target area, located in very rugged terrain, do not exist in the <br />layer of interest. In their absence one can only speculate about where and when the AgI plumes <br />were transported. <br /> <br />6.0 SUMMARY AND RECOMMENDATIONS <br /> <br />By far the most important finding of this study is that only limited silver from AgI plumes <br />was found at nine of the ten target snow sampling sites during snowfall events. Only six of the ten <br />sites had any indication of Ag above a background of 5 ppt, and only Michigan Creek showed <br />significant silver concentrations in the seasonal snowpack. Absence of much silver enhancement in <br />the target area silver suggests that most of the clouds over the target area were not seeded on a <br />routine basis. On some occasions those stations with silver levels from 7-14 ppt may have been <br />under AgI plumes, but no meaningful seasonal sno'\Nfall augmentation should be expected at the <br />nine stations with only background to quite limited silver concentrations. It is concluded from the <br />silver-in-snow evidence that the AgI generator network, as configured and operated during the <br />DWB-sponsored 2002103 winter program, did not succeed in routine seeding of most of the <br />intended target area. This result is likely caused by a combination of relatively low emitted AgI <br />amounts over the course of the winter, and frequent trapping or mistargeting of AgI plumes. The <br />actual amount of AgI emission is admittedly estimated, not known. Presumably it could be <br />calculated from seeding logs. <br /> <br />It is strongly recommended that any future winter orographic seeding operations in the same <br />area be preceded by at least a limited transport and dispersion project. The ability to routinely seed <br />the intended cloud regions should be physically demonstrated in the region of interest by plume <br />tracing of AgI andlor tracer gases or aerosols prior to any large-scale deployment of a new generator <br />network. Such work could be assisted by utilization of sophisticated atmospheric models such as <br />the Colorado State University RAMS model. This is not intended to imply that current knowledge <br />does not permit routine seeding of winter orographic clouds in many regions, especially with less <br />complex terrain. Several studies cited in this report showed routine targeting when AgI generators <br />were operated more than halfway up windward mountain slopes. This approach usually requires <br />use of radio-controUed AgI generators because of the need to operate them in remote locations. <br />Such a seeding operation is certainly more expensive than using manual generators, which can <br />readily be reached by people living in the area, but it has the large advantage of actually and <br />routinely seeding the clouds. <br /> <br />Another approach that has certain advantages and disadvantages was recently recommended <br />by Super (1999b) for use in Northern Colorado. It would use completely automated propane <br />dispensers sited far up windward mountain slopes within the clouds. Ice crystals are produced in <br /> <br />26 <br /> <br />