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<br />002493 <br /> <br />As the precipitation profile studies develop, similar data will be <br />available for other elevational zones. These estimates should be <br />obtained on a weekly oasis or, if needed, just prior to forecast. <br />The capacity of the snowpack to retain excess water will determine <br />whether seeding can be conducted for precipitation augmentation <br />(melting level below 2590 m (8500 ft) or strictly for snow aug- <br />mentation (melting level below 1830 m (6000 ft)). <br /> <br />MBA said its suggested procedures in forecasting the seedability <br />criteria are based on three modes of operation: operational <br />readiness, alert, and standby. These essentially refer to the extent <br />of project manning at any given time and the emphasis placed on <br />maintenance and analysis program personnel. <br /> <br />Seeding Techniques <br /> <br />, <br />t <br />I <br />I <br />i <br />I <br /> <br />The hypotheses developed by MBA for the SCPP dictate two alternate <br />seeding techniques - surface generators for orographic storms and <br />airborne generators for convective elements. In general, Sierra <br />Nevada wintertime storms exhibit both characteristics to a certain <br />extent, and a mix of techniques is applicable. MBA developed a <br />generator siting criteria based on the assumption of two windspeed <br />classes separated by a windspeed of 14 m/s. With these criteria, <br />MBA suggested the following forecasting requirements: <br /> <br />"1. Mean Layer Wind <br /> <br />a. The 700 mb flow should be predicted 12 hours prior to <br />declaration of experimental day, with periodic updates as <br />described in the experimental design. Various standard <br />prediction methods are in use. The choice is at the <br />discretion of the project forecaster. <br /> <br />I <br /> <br />r <br /> <br />b. Using forecast, declaration of southerly or westerly storm <br />is made based on trajectory of air mass. If the moisture <br />source is south of Monterey (700-mb wind 1800 to 2500), the <br />storm is southerly; a more northerly moisture source defines <br />a westerly storm. There are some situations during which <br />this is not precisely defined and judgment should be used. <br /> <br />c. Westerly storms have less imbedded convection, and based <br />on the hypotheses, airborne seeding is not recommended in <br />general. Ground seeding should be used in order to maintain <br />a strict separation of the treatment with respect to each <br />hypothesis. However, in the presence of a strong inversion, <br />airborne seeding may be necessary. <br /> <br />18 <br />