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<br />on a workstation, it does offer the ability to utilize the model in a field environment, enabling an <br />operational application in a field environment. ' <br /> <br />8.],]. Super, Arlin B., 1994: Implications of early 1991 observations of supercooled liquid water, <br />precipitation and silver iodide on Utah's Wasatch Plateau. J. Weather Modification, 26, 19-32. <br /> <br />ABSTRACT <br /> <br />The Utah/NOAA Atmospheric Modification Program conducted an observational program in early 1991, <br />with additIonal support from the Bureau of Reclamation. A summary is presented of observations <br />obtained on the Wasatch Plateau of central Utah which includes SL W (supercooled liquid water), <br />precipitation, AgI (silver iodide) IN (ice nuclei), air and dewpoint temperature, and wind velocity. With <br />the exception of AgI ice nuclei, measurements were made on 20 days with storm conditions. Silver iodide <br />was monitored during part or all of a subset of 12 days when valley Agl generators were being operated. <br /> <br />It is shown that abundant SL W existed during many hours, and a large fraction of these house did not have <br />precipitation observed on top of the Plateau. The SL W flux over the Plateau-top's windward edge <br />exceeded the average precipitation on top of the Plateau. These findings suggest significant seeding <br />potential may exist. <br /> <br />..' <br /> <br />Acoustical ice nucleus counter observations were adjusted to temperatures typical of AgI plume tops. <br />Aircraft measurements showed the plume tops were usually less than 1 km above the Plateau. The <br />adjusted ice nucleus observations suggest effective AgI ice nuclei concentrations were too low for <br />productive seeding much of the time when SLW was present. The main problem appears to be the warm <br />temperatures of the SL W during most storm periods. Effective concentrations of AgI ice nuclei are not <br />expected at such temperatures with the generators and release rates used in the Utah operational seeding <br />program. However, these estimates were based on a 1981 generator calibration in a cloud simulation <br />laboratory which may not be totally.representative.ofwinter orographic clouds. Direct observations are <br />needed of ice particle concentrations caused by seeding orographic clouds for the range of conditions <br />typical of winter storms. . <br /> <br />The challenge is to develop means of routinely targeting the SL W zone with adequate concentrations of <br />seeding-caused ice crystals which can start the precipitation formation processes in naturally inefficient <br />clouds. A number of approaches are suggested which could make the Utah operational seeding program <br />more effective. <br /> <br />CONCLUSIONS AND RECOMMENDATIONS <br /> <br />The 1991 data set is encouraging in that many hours had abundant SL W over the west edge of the Plateau <br />top. A large fraction ofthe wetter hours had no detectable precipitation, suggesting significant seeding <br />potential may exist if ice crystals can be produced in the SL W cloud. The average SL W amount during <br />the wetter hours with precipitation was even higher than during the wetter hours with no precipitation, <br />again suggesting seeding potential. <br /> <br />Huggins et al. (1992) presented estimates of SL W flux per storm episode for the 1991 field season. For <br />the 20 days discussed here, the estimates of total SL W flux exceeded 2100 Mg per meter of crest line. If <br />that amount of water was converted to precipitation of uniform intensity over the width of the Plateau , <br /> <br />52 <br />