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Created 12/26/06 1 <br /> EXHIBIT L <br /> �e WWC-Vail/Beaver Creek <br /> Record of Decision <br /> Vail Public Library-Public Hearing <br /> September 212010 <br /> North American Interstate Weather Modification Council <br /> www.naiwmc.org <br /> "Facilitating the exchange of interstate/interprovincial atmospheric resource management information" <br /> Summary of Studies that Document the <br /> Effectiveness of Cloud Seeding for Snowfall Augmentation <br /> Prepared by Arlen Huggins,NAIWMC Chair <br /> Introduction <br /> A recent report completed for the National Academies of Science (NAS) entitled <br /> "Critical Issues in Weather Modification Research" (1) concluded that there was no convincing <br /> scientific proof of the efficacy of intentional weather modification efforts. The NAS report <br /> further stated that, "In some instances there are strong indications of induced changes, but this <br /> evidence has not been subjected to tests of significance and reproducibility". Several responses <br /> to the NAS report (e.g., 2, 3) have pointed to many positive findings in both summer and winter <br /> cloud seeding experiments. The Weather Modification Association response (3) provides a very <br /> detailed summary of pertinent findings related to rain enhancement, hail suppression and <br /> snowfall augmentation. The intent of this paper is to summarize only the results of well <br /> designed research projects related to seeding winter orographic cloud systems, which the NAS <br /> report admitted showed "strong suggestions of positive seeding effects". Numerous carefully <br /> conducted winter orographic cloud seeding experiments in the 1980s, 1990s, and early 2000s <br /> contributed much of the positive evidence to which the NAS report refers. In many instances the <br /> results of small-scale experiments were repeatable and in some instances the results were <br /> statistically significant. It is this positive evidence that most in the field of weather modification <br /> believe validates the use of cloud seeding for practical operational snowfall enhancement <br /> projects. <br /> What follows is a brief discussion which summarizes decades of research into the <br /> effectiveness of wintertime cloud seeding. With two exceptions, only peer-reviewed papers have <br /> been used as references. Included in the discussion is the generally accepted conceptual model <br /> for successful wintertime cloud seeding, and the findings of the most important experiments and <br /> projects that provided both physical measurements and statistical evaluations of results. The <br /> conclusion of this paper is that there has been ample evidence that wintertime cloud seeding is <br /> effective when the cloud conditions specified in the conceptual model exist. This paper also <br /> concludes and agrees with the NAS report finding that uncertainties still exist in this field, and <br /> should be rigorously studied in a broad new area of federally-supported research. <br /> The current NAIWMC membership includes state agencies in <br /> North Dakota,Kansas,Oklahoma,Texas,Colorado,Wyoming,Utah,Nevada and California <br />