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002liU3 Initial Information Package Williams Fork Hydroelectric Project FERC Project No. 2204 Kremmling is in a rain shadow created by the surrounding ranges and receives an average yearly total precipitation of only 11.3 inches with maximum precipitation occurring during the summer months of July and August.1O Rainfall during these months peaks in August and derives from thunderstorms brought into Middle Park by a monsoonal flow from the south and southwest. This flow is part of a larger circulatory pattern that brings moisture into Colorado from sources in the Gulf of Mexico and the Gulf of California. II Mean monthly temperatures range from 140 F in January to 620 F in July (Siemer 1977) and are less variable year to year than is precipitation. Winter temperatures show the greatest variation, in part because cold air drains from the surrounding mountain ranges and periodically pools in the Middle Park basin. Because evaporation is mostly proportional to temperature, the monthly net moisture balance for those months with above freezing temperatures can be estimated from the temperature and precipitation curves. Using long-term averages, there are no months when there is a net moisture loss, but this is I deceptive. When precipitation falls below the long-term average, net moisture losses occur in May through September. Depending upon the magnitude of the shortfall, partial to full drought conditions occur and occur frequently enough to be a baseline characteristic to which the nati ve vegetation in Middle Park is adapted. Winter snowpack in the North Fork of the Colorado River, a watershed that includes Middle Park, is summarized in Chagnon et al12. This watershed shows less interannual variation in snowpack than most other watersheds in the Rocky Mountain region. Chagnon et al. attribute this variation to prevailing moisture flows from the north and west and to the north-south orientation of the surrounding mountain ranges that block these flows. 13 10 Siemer, E. E. 1977 Colorado Climate. Colorado Experiment Station. Colorado Stale University, Fort Coltins. " Milchell, V. L. 1976 The Regionalization of Climate in Ihe Western United States. Journal of Applied Meteorology 15:920-27. Tang, M. and E. R. Reiter 1984 Plateau Monsoons of the Nor/henl Hemisphere: A Comparison Between North America and Tibet. Monthly Weather Review 112:617-6. p - Chagnon, D., T. B. McKee, and N. L. Doesken 1991 Hydroclimatic Variability in the Rocky Moumains. Water Resources Bulletin 27(5):733-743. 13 Chagnon, D., et al. 1976 The Regionalization of Climate in the Western Uni1ed States. Journal of Applied Meteorology 15:920-27. 10