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<br />placing the generators on high ridges between windward slope canyons, but still well upwind of <br />the crestline. Consequently, the frequency of AgI being effective will likely be less than <br />suggested by the cloud top temperatures previously discussed, even when adjusted to colder <br />seeding plume top altitudes. <br /> <br />Some have argued that valley seeding with AgI is the preferred method because more time is <br />available for the AgI to disperse to sufficiently high and cloud regions of the SL W cloud zone. <br />But unless transient gravity wave results in considerable vertical transport, the valley released <br />plumes can be expected to be confined to less than 2000 ft above the windward slopes. Even <br />aircraft observations over the downwind ridge of the two parallel barriers forming the Bridger <br />Range did not show additional vertical dispersion (Super and Heimbach 1988). That is, AgI was <br />still confined to the lowest 2000 ft over the barriers regardless of the upwind fetch. The authors <br />are unaware of any observational evidence which suggests greater vertical plume dispersion over <br />windward slopes than found over crestlines. That being the expected case, the AgI will often <br />need to be transported far up the mountain slope to have any chance of reaching sufficiently cold <br />temperatures to nucleate ice. Therefore, there should not be any advantage for early introduction <br />of AgI by valley releases as the AgI will still not activate until transported to sufficiently high and <br />cold altitudes over the windward slopes, if indeed sufficiently cold temperatures are reached. <br /> <br />Acknowledgements: The authors are pleased to acknowledge the helpful discussions with and <br />comments from Steven Hunter and Jon Medina of the Bureau of Reclamation, and Arlen Huggins <br />of the Desert Research Institute. The interest of Joe Busto of the Colorado Water Conservation <br />Board, and the funding support by his agency, are also gratefully acknowledged. This work was <br />funded by the Colorado Water Conservation Board through the Bureau of Reclamation. <br /> <br />8. References: <br /> <br />NOTE: All references cited in this report including the three appendices are included here <br /> <br />AMS, 1998: American Meteorological Society Policy Statement - Planned and inadvertent weather <br />modification. Bulletin American Meteorological Society, 79, 2771-2772. <br /> <br />Boe, B. A. and A. B. Super, 1986: Wintertime characteristics of supercooled liquid water over the Grand <br />Mesa of west em Colorado. J. Weather Modification, 18, 102-107. <br /> <br />Boe, B., G. Bomar, W. R. Cotton, B. L. Marler, H. D. Orville (Chair) and J. A. Warburton, 2004: The <br />Weather Modification Association's response to the National Research Council's report titled: "Critical <br />issues in weather modification research" report of a review panel. Journal Weather Modification, 36,53- <br />82. <br /> <br />Bruintjes, R. T., 1999: A review of cloud seeding experiments to enhance precipitation and some new <br />prospects. Bulletin American Meteorological Society, 80, 805-820. <br /> <br />Bruintjes, R. T., T. L. Clark and W. D. Hall, 1994: Interactions between topographic airflow and <br />cloud/precipitation development during the passage of a winter storm in Arizona. 1. Atmospheric Sciences, <br />51,48-67. <br /> <br />Chai, S. K., W. G. Finnegan and R. L. Pitter, 1993: An interpretation of the mechanisms of ice-crystal <br />formation operative in the Lake Almanor cloud-seeding program. J. Applied Meteorology, 32, 1726-1732. <br /> <br />Clark, T. L., 1977: A small scale dynamic model using terrain following coordinate transformation. J. <br />Compo Physics, 24, 186-215. <br /> <br />26 <br />