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reasonable agreement with field measurements of plume positions; however, plume concentrations were unpredicted. The model was run with a Kessler warm rain parameterization to examine the characteristics if liquid condensate. Patterns of liquid water predicted by the model suggest that depletion of liquid water to the lee of the crest could be due to subsidence warming. This complicates the estimation of liquid water depletion through precipitation processes. DISCUSSION The model results were in reasonable agreement with observations of plume positioning. The observed meandering of plumes, transport over lower terrain and shallow vertical dispersion were predicted by the model. The model's elevated concentrations were smaller than those inferred by SF6 observations. This is . likely for three reasons: 1) the tracer was given an instantaneous dispersal throughout one grid bin upon release; 2) the model predicted less vertical transport than reality; and 3) comparisons were done using peak SF 6 observations; however, the use of average SF 6 concentrations, though somewhat ambiguous, could not explain all the difference. The model illustrated several points which should be considered in planning future winter orographic weather modification operations which employ surface sources. · Seeding material can be confined to a depth of several hundred meters over the terrain. .., · The horizontal and vertical positions of the release point are critical. In this study the best release points were on the windward slopes of the barrier to take advantage of terrain-forced vertical motions. · Pooling of seeding material can occur in the valley areas, and its transport can be guided by the character of lower terrain. The most critical. factor in ground-based targeting is placing the Source in an area having positive vertical velocity near the surface. Typically, this is windward of the crest. Areas at the crest or just downwind showed small or negative vertical velocities in simulations. Valley sites can be poor locations because the vertical motion fields may not reach low enough and the valley surface winds are too poorly organized to provide consistent transport. The use of an upwind seeding site, e.g., the San Pitch Mountains, was modeled (not illustrated in this paper) and found to have some possibility of success. An upwind release site has the advantages of providing a broader plume, earlier nucleation and opportunity for greater vertical transport. The drawbacks include targeting inconsistencies, increased lead time and dilutiori. It would be worthwhile to try one or more test releases from the San Pitch Mountains using a mobile source of AgI. SF 6 is not the tracer of choice for this because of the large dilutions anticipated while crossing the Sanpete Valley. It would be useful to model transport and diffusion using a Lagrangian transport scheme. The Lagrangian treatment uses a coordinate system which follows effluent particles rather than remain'ing stationary. This eliminates the effect of the initial dispersion of tracer material and would give a better visual display of plume characteristics. A finer innermost mesh is needed to better simulate the effects of flow around the terrain of the experimental area. In particular, the canyons, which are important in the transport of low elevation seeding material, are not well-represented in the model. Finally, the model is being implemented on workstation environments. Though not possible to run the model with a fine resolution 51