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. DU .'. Fig. S. Regional analysis of moisture over the Arizona domain on January 17, 1979, at 1800 lTfC at SOO magi. The units of mixing ratio are g kg-I. The grid is desaibed in Figure 3. The rise of 1200 m along the south-to-nonh axis of transport and the series of organized mesoscale perturbations produced significant precipitation along the Mogollon Rim as shown in Figure 6. The cumulative precipitation totals from January 16 to 19 reached SO mm along the rim. Cumulative precipitation pauerns from January 1 to 17 at 0060 UTe clearly show the local influence of terrain on precipitation distributions as outlined by the 35-mm isohyet During the following 18 hours, heavy precipitation was predicted by the MM4 model. The distribution of this precipitation remained largely controlled by the terrain forcing as indicated by the 55-mm isohyet in the cumulative total at 0000 UTe on January 18 (see Fig. 6b). The distnbution and the quantity of precipitation in the MM4 model simulation generally matched the observed precipitation; however, the pauerns lacked the detailed structure resolved by the local-scale precipitation model described by Medina (1991). 4. CONCLUSIONS Large spatial and temporal variations in the regional controls of precipitation are clearly defined by the MM4 analysis. This model provides significantly more information regarding the physical evolution and structure of systems that produce precipitation than do either the GCMs or the synoptic scale observations. Therefore, sounding data derived from the MM4 model output at representative sites upwind and over watersheds will provide more representative initial conditions for local-scale precipitation models than will GCMs. These regional data should enhance performance of the local-scale precipitation model when used judiciously. Reclamation is in the early stages of developing the initialization and nesting procedures to automate the processing of this information. Results from the initial tests using MM4 soundings to initialize the precipitation model appear encouraging (Medina 1991). ~, , . . . '. . DIU . b DIlA Fig. 6. ~M4 analysis of cumulative precipitation (mm) over Anzona from January I, 1979, to January 17, 1979, at 0600 (a) and January 18, 1979, at 0000 UTe (b). 5. FUTIJRE PlANS Furtb.~r analysis and sensitivity testing will be performed to determine the most representative soundin.gs and efficient initialization procedures for five typIcal western watersheds. Once the interfacing between the MM4 soundings and the local-scale precipitation model is completed. tests will be conducted usU18 CCM- and MM4"erived soundings separately to evaluate the additional information from nested MM4 climate simulations. Data from the recently ~eported n<:sted..climate studies of Giorgi (1990) WIll be used 10 thIS evaluation. When the modeling system is fully evaluated ~d ready for climate change simulations, future cli~ate scenarios will be examined for western basins usmg output from nested MM4-CCM simulations representing doubled-COl and normal conditions. Results from tlle local-scale precipitation model will then be used to meet Reclamation's water resources management rc~uirements as described by Dennis (1991).