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<br />002485 <br /> <br />"Winter precipitation in the Sierra Nevada can be characteri- <br />zed by the storm's source of moisture. In general, southerly <br />moisture sources are associated with storms which have large <br />amounts of water as both vapor and liquid. They are unstable, <br />with inherent convection which can release intense precipitation. <br />By contrast, more westerly sources of moisture are associated <br />with more stable or orographic storms. Since these storms <br />are basically colder, they have less total moisture which can <br />precipitate from the clouds when the storms advance to the <br />Sierra Nevada. Condensation is caused by the lifting and <br />cooling of the air as it rises over the mountain terrain, <br />resulting in precipitation which is generally less intense <br />but longer in duration than that from convective storms." <br /> <br />Review of Previous Cloud Seeding Research <br /> <br />Previous weather modification programs were reviewed and classified <br />in terms of their applicability to the study effort on two bases. <br />These were: <br /> <br />. Their meteorological relevance to Sierra Nevada storm conditions <br />or the degree to which the results could be considered representative <br />of the Sierra Nevada. <br /> <br />. The amount of supporting operational and research data available <br />upon which to base inferences and conclusions with respect to the <br />design of the SCPP. <br /> <br />Programs studied during the review included the Pacific Gas and <br />Electric (PG&E) Lake Almanor program, The Sacramento Municipal <br />Utility District (SMUD) American River program, the Kings River <br />Water Conservation District program, CENSARE, the Colorado State <br />University Climax program in the central Rocky Mountains, and three <br />sponsored by the Bureau of Reclamation: The Colorado River Basin <br />Pilot Project (San Juan), the University of Nevada Pyramid Lake <br />Pilot Project, and the University of Washington program in the <br />Cascades. <br /> <br />t <br />I <br /> <br />Maximum concentration was placed on the CENSARE data because of its <br />relative completeness and the physical proximity of CENSARE to <br />the study area. The Pyramid Lake and Lake Almanor data led to <br />strong inferences concerning differences between the basic lee <br />side characteristics of Sierra precipitation found in those areas <br />as contrasted with the American River Basin and the CENSARE project <br />area (Mokulemne and Stanislaus Basins). <br /> <br />10 <br />