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<br />1. INTRODUCTION <br /> <br />The Sierra Cooperative Pilot Project (SCPP), administered by the Bureau of <br />Reclamation, has measun~d'and st.udied supercooled liquid water:. within \...infer ". <br />storms affecting the central Sierra Nevada mountains of California and Nevada. <br />This research was part of the program's overall objective which was to develop a <br />firmer foundation for operational \Neather modification programs in the region. <br />Historically, operational programs have been conducted in ten Sierra Nevada <br />river basins (see Fig. 1) over the past 10 years. These operational programs <br />emphasize the interest in California and Nevada to use weather modification to <br />solve long term water needs. The SCPP has attempted to respond to this interest <br />with a scientific investigation to provide a basis for weather modification <br />operations. The results presented here provide comprehensive analyses of SCPP <br />research concerning cloud seeding opportunity recognition. <br /> <br />Early studies in the SCPP concentrated on airborne investigations of super- <br />cooled water and ice crystal distributions in clouds (Heggli et al., 1983). <br />These studies indicated that the largest ratios of supercooled water content to <br />ice crystals existed in the po~t-frontal convective clouds. Very little super- <br />cooled water was observed in the area-wide frontal clouds or the shallow <br />orographic clouds. Soon after these results were published, supercooled water <br />measurements became available from ground-based instrumentation, particularly <br />the dual-channel radiometer. Icing rate measurements also became available from <br />mountaintop weather stations. <br /> <br />These new observation tools provided the technology for renewed exploration <br /> <br />of supercooled water within storms. Measurements of supercoolE~d water by these <br /> <br />instruments led to the realization that aircraft measurements provided an <br /> <br />1 <br /> <br />I <br />