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! . EXECUTIVE SUMMARY This document presents a proposed weather modification program of applying operational cloud seeding technology to enhance the winter snowpack in high-elevation mountainous areas of north-central Colorado and southern Wyoming (hereafter Headwaters Region) and consequently, provide additional streamflow to the North Platte River. Government officials and others are looking at several options for adding water to the river. The Secretary of the Interior is charged with the responsibility for development of the water resources of the Colorado River Basin (Colorado River Basin Project Act, 1968; Public Law 90-537), the protection of water quality (Colorado River Basin Salinity Control Act, 1974; Public Law 93-320), and the transfer of precipitation management technology (Reclamation States Emergency Drought Relief Act, 1991; Public Law 102-250). Several options are under consideration to provide additional water including reservoir management. Cloud seeding technology improvements in the past 20 years now provide a logistically feasible and cost-effective option to enhance fresh water resources in some mountain watersheds of the western United States. The proposed program consists of two principal components, a cloud seeding design phase and the operational seeding phase. Lessons learned in previous cloud seeding studies indicate that each area presents hurdles to cloud seeding that are site specific. The proposed three-year design phase is aimed at conducting field and modeling studies to determine the proper approach, equipment, and installation sites appropriate for the Headwaters Region. Additionally, the design phase will enable dealing with environmental compliance and the conduct of associated studies. No cloud seeding can take place until compliance is achieved. Because average winter precipitation is expected to increase in the Headwaters Region from cloud seeding, environmental compliance efforts for a possible Environmental Assessment or Environmental Impact Statement are estimated to require three years for completion. Intended benefits of a three-year design include the development of an evaluation design proper for operational seeding in the Headwaters Region. The operational seeding period is structured for 10 years (equipment, permits, environmental compliance) and will involve automated cloud seeding systems that largely self-determine when seeding is appropriate and then proceed to treat clouds. Data collection is also expected to be largely automated. All data collection and cloud seeding system types should be installed and tested in the design phase. Regarding the scientific support for cloud seeding, current policy statements of the American Meteorological Society and the World Meteorological Organization state that statistical analyses of some cloud seeding programs have suggested mountain snowfall increases of 10 to 15 percent per winter. Cloud seeding experiments conducted and/or supported by the Bureau of Reclamation in the 1980-90s have contributed sorely needed physical measurements and analyses that documented cloud and precipitation responses to cloud seeding and indicated that specific areas can be targeted for treatment effects. These studies along with the substantial improvement in computer modeling of weather and clouds provide methodology that can be applied to seeding winter clouds in the Headwaters Region and expect to obtain measurable additional precipitation. Seeding trials conducted on winter clouds in the Grand Mesa of west-central Colorado and the Wasatch Plateau of Utah repeatedly indicated a precipitation increase response to seeding (see appendix A, sections 7 and 8, for details and references). Those studies did not include a component of statistical evaluation of precipitation, but were rather structured for physical measurements. To develop estimates of additional water from cloud seeding in the Headwaters Region, enhancement results of about 25 v