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<br />2.0 SUMMARY <br /> <br />2. 1 <br /> <br />Justification and Objectives <br /> <br />The general process of precipitation utilization in the Sierra <br />Nevada consists of two phases. The first phase occurs during most of the <br />winter in which a part of the reservoir volume is kept empty for flood <br />contingencies by permitting outflow through the hydroelectric generators, <br />and spilling the water in excess of generator capacity. In the second phase, <br />generally during the spring, streamflow is collected to fill the flood control <br />volume for storage and use through the summer. One objectives of a snow- <br />pack augmentation program is to redistribute the precipitation so that the <br /> <br />r <br />reservoir outflow which is not used for electrical generation is minimized <br />throughout the year. Thus, rather than water afOainfall being spilled past ~ <br />the hydroelectric generators, the ideal situation would have this water stored <br />as snowpack to be utilized during the snowmelt and summer seasons. <br /> <br />2.2 <br /> <br />Background <br /> <br />Winter precipitation in the Sierra Nevada can be characterized <br />by the source of moisture of the causative storm. In general, southerly <br />moisture sources are associated with storms which have large amounts of <br />water as both vapor and liquid. They are unstable, with inherent convection <br />which can release intense precipitation. By contrast, more northerly sources <br />of moisture are associated with more stable storms. Since the storms are <br />basically colder, they have less total moisture which precipitates from the <br />clouds when the storms advance to the Sierra Nevada. Consideration follows <br />from the lifting of the air parcels by the underlying terrain resulting in <br />precipitation which is generally les s intense than that from convective storms, <br />but with a longer duration. <br /> <br />2.3 <br /> <br />Hypotheses <br /> <br />The hypotheses of this experiment follow from the classification <br />of the storms into the two classes. Basically the pilot project will modify the <br />two storm types with separate objectives. The orographic (westerly) storms <br />will be seeded to increase the efficiency of the storm, and therefore to augment <br />the precipitation in these cold systems. The procedure will be to seed the <br />storms at light seeding rates to avoid overseeding. Seeding will be done with <br /> <br />3 <br />