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~ 58 JOURNAL OF WEATHER MODIFICA nON Volume 38 Simulations of Snowpack Augmentation in the Colorado Rocky Mountains William R. Cottonl, Ray McAnelly', Gustavo Carri61, Paul Mielke', and Curt Hartzell2, CCM IColorado State University Department of Atmospheric Science Fort Collins, CO 80523 2631 Knoll wood Dr., Willmar, MN 56201 Abstract. In this paper we summarize a project designed to evaluate the feasibility of using a mesoscale model to support cloud seeding operations and the physical evaluation of seeding responses. The model used was the Colo- rado State University Regional AUnospheric Modeling System (RAMS). RAMS provided forecasts of precipitation and winds for the 2003-2004 winter season. Detailed evaluation of model forecast orographic precipitation was per- formed for 30 selected operational seeding days. In addition, the model was run to emulate cloud seeding operations performed by Western Water Consultants. It was shown that the model can be a useful forecasting aid in support of the seeding operations. But, the model over-predicted precipitation, particularly on moist southwest flow days. This was likely due to over-simulated convection when little or only relatively shallow convection actually occurred. The model also exhibited virtually no seeding response in terms of precipitation. Possible reasons for that are discussed. 1.0 INTRODUCTION The Colorado Weather Damage Modification Program (WDMP) research project involved a physi- cal evaluation of the Denver Water (DW) operational winter orographic cloud seeding program in the cen- tral Colorado Rockies for the winter season 2003- 2004 using the Colorado State University 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 Fig- ure 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. A collaborative gen- erator network (funded by DW, ski areas, and other entities) consisted of up to 56 generators that were available for seeding operations. 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 pe- riod of operations with a number of improvements derived from assessments of the real-time runs, and then rerun with simulated seeding generators releas- I Corresponding author address: William R. Cot- ton, Dept of Atmospheric Science, Colorado State University, Fort Collins, CO 80523-1371, cot- ton@atmos.colostate.edu - Reviewed - ing seeding material (AgI) at rates, time periods, and locations consistent with the operational program (Hartzell et al., 2(05). In Section 2.0 we describe the RAMS setup, in Section 3.0 we summarize the results from this pro- ject, in Section 4.0 we provide an overall discussion of the results and in Section 5.0 we provide recom- mendations for future operations. 2.0 RAMS SETUP The 2003-2004 prototype real-time forecast ver- sion of RAMS@CSU was based on version 4.3. The physics of the model is described in some detail in Cotton et al. (2003). Briefly, the microphysics of the model is a bulk microphysics scheme in which the size-distribution of all hydrometeors is determined by a prescribed generalized gamma distribution. In con- trast to most bulk models, however, the physics is explicitly represented by emulating a bin model in- cluding explicit activation of cloud droplets and ice particles on cloud condensation nuclei (CCN) and ice nuclei (IN), stochastic collection among all hydrome- teors using state-of-the-art collection kernels, and a bin representation of sedimentation of hydrometeors. The ice phase is composed of pristine or vapor-grown ice crystals including a variety of habits defined by temperature, snow which represents partially-rimed vapor-grown ice particles, aggregates, graupel, and hail or frozen raindrops.