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<br />fraction, but never all, of the seasonal flux of SL W to snowfall. Thus, the SL W flux represents an <br />absolute maximum amount of water greater than the amount cloud seeding can convert to precipitation. <br />The fraction of SL W that could be converted to snowfall by an optimally designed and conducted cloud <br />seeding program can only be estimated. However, if the seasonal flux of SL W over the area of interest <br />were not a significant fraction of the seasonal precipitation that falls on the area, or of the seasonal <br />streamflow that flows from the area, it would have to be concluded that cloud seeding potential was <br />limited. But even limited potential might be economically attractive is some regions where the benefits <br />of additional water are high. <br /> <br />Some estimate of the available SLW, the basic "raw material" for cloud seeding to be effective, should <br />be made in a feasibility study. Fortunately, such estimates have been made practical the past several years <br />with microwave radiometer observations (Hogg et al., 1983). These measurements of integrated SL W <br />have been made at a number of locations in the West, including two in the Sevier River Drainage (Tushar <br />Mountains and Wasatch Plateau). <br /> <br />It will be shown in section 3 that a significant SL W flux has been observed over the area of interest and <br />over other barriers in the West It is, therefore, reasonable to consider other pertinent questions. For <br />example, what are the meteorological conditions (slonn stage, wind velocity, stability, cloud thickness, <br />etc.) that accompany SL W? This infonnation relates to experimental design and to when operational <br />seeding should be done. The spatial distribution of the SL W is important for consideration of where and <br />at what temperatures nucleation of ice crystals is possible. Thus, it is useful to know the typical position <br />of the SL W cloud relative to the mountain barrier. <br /> <br />Once the spatial and temporal distributions of SL W are reasonably understood, attention should be turned <br />to the T &0 (transport and dispersion) of the seeding agent. The T &D of both airborne- and ground- <br />released AgI involve complex processes of airflow and turbulence near rugged terrain. In addition, recent <br />work over the Wasatch Plateau has demonstrated the importance of even weak embedded convection in <br />the T &D of valley-released AgI. ' <br /> <br />Once the ability has been demonstrated to routinely transport AgI to the SL W zone in appropriate <br />concentrations, other questions remain. The volume filled with AgI, nucleation rates, and subsequent ice <br />crystal growth ahd fallout rates all need to be considered. It should be documented whether a significant <br />fraction of the crystals grow to snowflakes or snow pellets which fall to the surface before sublimating <br />in the lee of the barrier. <br /> <br />5 <br />