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for two winters only, a short climatological record compared to the more traditional Snow Telemetry (SNOTEL) and snow course datasets. Unlike these datasets, however, SNODAS provides spatially continuous data at 1 km resolution. The model has been validated7 in the Colorado Mountains against the Corps of Engineers widely-validated SNTHERM model. 2.1 Determination of Target Areas A major variable in estimating water yield from seeding will be selection of the seeding target areas. We split this task into two sections: existing areas already being seeded by operational programs (in Utah and Colorado only), and potential new areas. Geographic Information Systems (GIS) maps were obtained for the former. Selection criteria for existing areas vary, but are in general elevation-based. In Utah, this criterion is 7000 feet or higher, whereas in Colorado it is above 8000-9000 feet. These criteria were informally adopted and reflect the higher elevations in Colorado. In any event, the existing areas were used as provided, with no modification except to exclude parts outside the Colorado River drainage area. The existing target areas are listed in Table 2. Table 2. Existing Target Areas Colorado Utah 1. Upper Arkansast 11. Fishlake Mtns. T 2. Gunnison North 12. Boulder Mtn. T 3. Gunnison South 13. Uinta Mtns. South 4. Vail 14. Dixie Natl. ForestT 5. Beaver Creek 6. Grand Mesa North 7. Grand Mesa South 8. San Miguel Mtns. 9. Western San Juans 10. Eastern San Juans T Portion of area outside Colorado River BaSin For potential areas, a strict 9000 foot base threshold was used as a criterion in the Colorado basin regions of Arizona, New Mexico Colorado, Utah, and Wyoming. This criterion follows that specified in a planning document8 for a winter cloud seeding research project called the Colorado River Snowpack Enhancement Test (CREST). Further criteria from this document were that the candidate region usually has at least 20 km west-east extent of 9000 feet elevation area and that it is largely or wholly outside designated wilderness areas. These criteria were used to select proposed areas for cloud seeding experimentation, whereas this document is concerned with all potential target areas for operational seeding. It would be impractical to conduct experimentation within a wilderness area, since key instrumentation would not be allowed. Some operational projects target wilderness areas, although their seeding generators are located outside their boundaries. So for the present study, several additional areas, including those with wilderness designations and barriers no wider than 5 km, have been added. Finally, the potential new areas were included only ifthey are outside existing target areas. 2