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<br />The frequency of sufficiently cold SL W cloud for effective AgI seeding largely depends on <br />two factors. First is the mountain elevation, with higher mountains expected to have colder <br />clouds, and second is the geographic location, with more southerly mountains expected to have <br />wanner clouds. In all observational sets available for this report, a relatively high fraction of the <br />observations were too warm for conventional AgI seeding. However, operating AgI generators <br />directly within cloud penn its the forced condensation freezing mechanism to function, resulting <br />in very high seeded crystal concentrations immediately downwind of the generator if the <br />temperature is -60C or colder. Silver iodide released below cloud will need to reach SL W <br />temperature colder than about _80C to produce target zone seeded crystal concentrations in excess <br />of about 20 per liter, considered the minimum value to produce more than trace snowfall rates. <br />Such concentrations can be achieved with propane dispensers if the temperature is -20C or <br />colder. Consequently, propane seeding can be effective over a wider range ofSLW cloud <br />temperatures. <br /> <br />The choice of AgI or propane, or perhaps both, should be based on a number of factors. Both <br />have advantages and disadvantages as discussed in this report and a number of cited articles. <br />There is no "one size fits all" seeding approach that is best for all mountain ranges and <br />geographical locations. The numerous investigations cited in this report provide important <br />guidance for designing specific area seeding projects. But in the end, each specific area should be <br />evaluated by persons with the appropriate technical and practical expertise, and experience in <br />winter orographic cloud seeding. Approaches which may seem reasonable when discussed in a <br />comfortable office may prove totally impractical in particular mountainous terrain during winter. <br /> <br />Also, seeding project designers should be careful to avoid the temptation to apply dated, almost <br />"traditional," seeding approaches to new areas because they were once believed to be effective <br />elsewhere. Remnants of approaches used during the 1960s Climax Experiments are still evident <br />in some operational seeding projects in spite of later serious challenges to Climax statistical <br />results, and to the large but unsuccessful Colorado River Augmentation Pilot Project (1970-75) <br />which was based in large part on Climax results. A considerable body of more recent knowledge <br />exists, because of much improved instrumentation and computer modeling. There is no valid <br />excuse for ignoring that knowledge, especially regarding valley seeding plume transport <br />limitation and SL W cloud locations, variability and often mildly supercooled temperatures. <br /> <br />iii <br />