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. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . EXECUTIVE SUMMARY The Colorado Weather Damage Modification Program (WDMP) research project involved a physical evaluation of the Denver Water (DW) operational winter orographic cloud seeding program in the central Colorado Rockies for the winter season 2003-2004 using the Colorado State University mesoscale Regional Atmospheric Modeling System (RAMS). The project was piggy-backed onto the DW operational program contracted by Western Water Consultants (WWC), LLC. The target area was the Blue, Upper Blue, Snake, Williams Fork, and Upper South Platte River drainage basins above 9,000 feet elevation (see Figure 2.1). The area within the target boundary was about 3,700 km2. From February 10 through March 2004 only the Upper South Platte River basin and along the Continental Divide above the Upper Blue River basin was to be targeted. Using a finest grid spacing of 3-km, RAMS was run first in real-time to provide operational support to the DW cloud seeding program. RAMS was subsequently rerun for the period of operations with a number of improvements derived from assessments of the real-time runs, and then rerun with simulated seeding generators releasing seeding material (Agl) at rates, time periods, and locations consistent with the operational program. As a mesoscale model, RAMS is unique in its ability to explicitly represent the activation of cloud nucleating aerosols (CCN and IN) including seeded IN, to simulate the transport and dispersion of seeding material, the explicit nucleation and vapor deposition, riming, and aggregation growth of ice particles, and amounts and types of precipitation. Moreover, it was able to do so for an entire operational cloud seeding program. We believe that this project establishes a "model" of a methodology for physical and statistical evaluation of future seeding projects. However, it must be recognized that this was a first prototype model and as such things did not work out entirely according to our expectations. The major results of this research project are as follows: . WWC (Larry Hjermstad) found that after the model fixes had been implemented in mid-February 2004 and the RAMS real-time forecast 0000 UTC cycle was run on the new PC cluster, the forecast output that was posted on the Web site was very useful. The low-level warm temperature problem had been greatly reduced and the model provided timely input for operational cloud seeding decision making. There were numerous forecast products and parameters to evaluate. In addition to the 2-hr forecast presentations, the animated forecast loops provided a quick visual picture of changes over time. . Larry Hjermstad did point out the forecast model exhibited a warm temperature bias at 700 mb which reduced its effectiveness as a decision tool for determining if seeding operations should proceed. Causes of the warm bias were determined and fixes were made in mid-February 2004. The entire winter season was re-run to provide a better estimate of natural xv