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. '. on a large number of cases. Initial Clark model simulations are examining model sensitivity to initial conditions and increased resolution of complex terrain in western Colorado using rawinsondes and MM4 soundings. Initialization and Assessment of Model Simulations Giorgi and Bates (1989) began a validation of the CCM-MM4 nested modeling approach using observations for 40 months from January 1982 to December 1983, and January 1988 to April 1989. They used initial conditions from ECMWF (European Center for Medium-range Weather Forecasts) analyses of observed data gridded to a spatial resolution of2.8 by 2.8" and having a temporal resolution of 12 h. MM4's lateral boundary conditions were adjusted every 12 h using the ECMWF gridded data. These initial conditions were located at grid points that matched the CCM T-42 (triangular spherical harmonic truncation at wave number 42) used'in climate simulations. Giorgi et al. (1992a) have validated mean monthly precipitation predicted by the MM4 model during the 1982-83 and 1988-89 periods. They found that the correlation coefficient between observed and modeled monthly precipitation varied from 0.53 to 0.94 among each of six subregions of the Weste~rn United States. Over the Central Rocky Mountains, cold season precipitation was reasonably well simulated with a bias of 40%, however, the warm season bias was 157% in the base runs. The revised horizontal diffusion method lowered this bias to.39% in the 1988- 89 simulations. Giorgi et al.(1992a) defined bias as the sum of the differences between observed and model-predicted daily average precipitation in each subregion, divided by the total number of station days for that subregion and season. This model bias is a direct measure of the model error simulating a given variable over a region. Their study was based on 390 daily observation stations in an area of -4.4 million km2 in the West. The station density was about 11,000 km2 per gauge with few high elevation gauges. This study focuses on the assessment of local area precipitation in complex terrain using a higher density of - 930 km2 per gauge with 11 gauges above - 2700 m ms!. Modeled precipitation was compared with surface precipitation data from NWS (National Weather Service) offices and cooperative stations, and the Soil Conservation Service's SNOTEL (snow telemetry) remote high elevation automatic stations. Figure 2a shows a time-series comparison between observed high elevation cumulative precipitation and MM4-predicted cumulative precipitation in the Gunnison region during the 1982-83 water year (October I to September 30). Predictions by MM4 were averaged over 8 grid points in the vicinily of 31 precipitation gauge sites. Model daily average values and gauge averages were accumulated to form model and observed daily cumulative means. This daily cumulative mean gives a measure of the total precipitation observed from the beginning of a water year to a given date. Precipitation observations were stratified by three elevation zones: < 2100 m, 2100 to 2700 m, and > 2700 m msl and similarly accumulated into three daily cumulative means. Figure 2a shows the time series of daily cumulative precipitation observed 4 Matthews et al.