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<br />. A meteorological analysis should be made to determine if <br />cloud seeding will have a significant effect on freezing level of precipitation <br />clouds. If so, the impact of this on snowfall distribution should be evaluated. <br /> <br />. Theoretical and observational studies should be carried on <br />before and during the pilot project to determine more adequately whether <br />weather modification in the Sierra Nevada will normally produce a longer <br />storm duration, a greater rate of fall, or a combination of the two. <br /> <br />. Prior to initiation of any pilot weather modification program <br />in the Sierra Nevada, the best available meteorological models and analyses <br />should be used to formulate testable hypotheses about downwind effects (or lack <br />of such effects) of cloud seeding over this specific region. During the pilot <br />project, these hypotheses should be carefully tested. ThB testing should <br />involve both a properly designed expanded rain gage network and meteorological <br />studies of the atmospheric water balance of the region. <br /> <br />In the general sense, cloud seeding will influence precipitation <br />by affecting rate and redistributing the areas of precipitation. Duration of <br />precipitation will not be affected by more than a few hours because of the <br />inefficiency of seeding post-frontal cloud bands and because precipitation <br />enhancement depends on the presence of natural potential. The precipitation <br />may be redistributed up- or down- slope, depending on seeding rates and <br />whether the precipitation is orographic or convective. The altitude of the <br />precipitation determines the physical characteristics; whether rain, graupel <br />or snow falls depends on the temperature and hence is related to the elevation. <br />However, adjustment in the freezing level is not an anticipated result of cloud <br />seeding. <br /> <br />The exact magnitude of precipitation augmentation parameters <br />depends greatly on local conditions. Hence, determination will depend on <br />extensive measurements taken as part of a Sierra Nevada Pilot Program. The <br />existing knowledge is derived from studies of winter orographic precipitation <br />in the Rockies, the Cascades, and limited areas in the Sierra Nevada. The <br />p:t;esent work indicates that convective elements of Sierra Nevada cloud systems <br />have significant seeding potential and deserve further study. In some situations <br />carry-over effects of seeding are possible. The proposed design includes <br />extensive precipitation networks covering both the target area and nearby <br />regions which may be affected by cloud seeding. <br /> <br />8 <br /> <br />__J <br />