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.. .. the western flight track is 10 km. In order for the plumes released from the valley to be continuous over the west track would require a generator spacing of 4.4 km based on an average dispersion angle of 23 degrees. The spacing utilized in the conduct of the Utah operational seeding program is approximately 16 km. The spacing of the eight generators utilized in the conduct of this research program was approximately 5-10 km. Both the spacing on the operational and research program would appear to be too sparse on the basis of these calculations. Future research needs to address this question in more detail. The authors believe the best way to gain quantitative information on this question is through multiple valley releases of SF 6' Co-location of SF 6 releases with silver iodide releases would also be very beneficial. This would allow an analysis of ice crystals concentrations and sizes within and outside SF 6 plumes. These SF6 plumes would be used to precisely ''tag'' the location of the silver iodide seeding material made possible by the very fast response time of the real-time SF 6 analyzer. It is difficult to assess how representative the results from this two month research program may be of the climatology of Utah winter storms. Both of the test cases discussed in this paper was post-frontal. Post- frontal conditions in Utah in winter are frequently more convective than pre-frontal. The presence of convection may be important in the vertical dispersion of ground released seeding material. . It is concluded from this discussion that in these two test cases, silver iodide could have been transported from a release site at the mouth of Birch Creek Canyon into environmental conditions that would lead to nucleation. NCAR counter observations provide independent confirmation of the transport of silver iodide nuclei, released from the valley floor, over the Wasatch Plateau. .... 8.4. Super, A. B., and A. W. Huggins, 1992a: Investigations of the targeting of ground-released silver iodide in Utah, Part I: Ground observations of silver-in-snow and ice nucleL J. Weather Modification, 24,19-33. ABSTRACT During the winter of 1989-90, the Utah Division of Water Resources, the National Oceanic and Atmospheric Administration, and the Bureau of Reclamation cooperated in a limited sampling project to investigate the transport and dispersion of silver iodide (AgI) cloud-seeding aerosol over two target.areas in the mountains of Utah. Seeding was done using the ground-based AgI generator network of the Utah operational cloud seeding program. Transport and dispersion over the Wasatch Range and Wasatch Plateau were evaluated using a silver-in-snow sampling technique and the real-time detection of AgI aerosol and sulfur hexaflouride gas. This report contains an extensive review of past silver-in-snow results from several different regions as a basis for comparison with the current study. The 1989-90 Utah results indicated that a low percentage (<15 percent) of bulk snow samples from 10 mountain target area locations had silver (Ag) concentrations above values for periods when seeding had been conducted. Consistently poor targeting and/or low seeding generator output could explain the general lack of detectable Ag in the two Utah target areas. Seeding generator output also forms the basis for estimates of average ice particle masses required to achieve the greater than 11 percent snowfall increase reported from statistical analyses of the Utah operational pr~gram. These estimates are based on very optimistic assumptions (perfect targeting, 100 percent nucleation, 100 percent fallout, etc.) They indicated that snowfall enhancements of 10 percent or greater are unlikely with the current AgI seeding rate of 6 grams per hour used in Utah. 41 L