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<br />002486 <br /> <br />Review of Models <br /> <br />MBA identified four basic areas of possible application of models to a <br />Sierra Nevada pilot program. These were: <br /> <br />"Forecasting: the technique for identifying potentially <br />seedable situations. <br /> <br />"Operations: the operational determination of proper delivery <br />and seeding rates. <br /> <br />"Evaluation: the assessment or evaluation of seeding results. <br /> <br />"Research: the interpretation and extension of field data <br />for improved physical understanding." <br /> <br />Since atmospheric simulation models are generally discussed in terms <br />of their treatment of the two general areas of dynamics and micro- <br />phYSics, MBA reviewed the status of existing model capability and <br />necessary improvements with respect to each of these areas. <br /> <br />"Since the primary purpose of a Sierra Nevada pilot project <br />will be to determine how seeding will alter precipitation <br />patterns, the model must include a complete coupling of the <br />dynamics with the microphysics. Most current models empha- <br />size either microphysical processes within the cloud using <br />simplified dynamics or stress the dynamics with simplified <br />microphysics. In the case of orographic precipitation, <br />such a separation is not appropriate, since the microphysics <br />can alter the air motions drastically. Further, the Sierra <br />Nevada storms are frequently characterized by imbedded con- <br />vective bands, further complicating the coupling of dynamics <br />and microphysics as well as requiring modeling of two sub- <br />stantially different regimes for both. <br /> <br />"With these comments in mind, it does not appear that any <br />existing models in their present form will be adequate <br />for an operational project, although some may be useful <br />as research tools to aid in understanding air flow in and <br />about the mountains and how clouds might be altered by <br />seeding. Operational techniques will involve parameterized, <br />three-dimensional models that have been carefully calibrated <br />by compa ri ng thei r results with real data." <br /> <br />Snowfall Climatology <br /> <br />The general large-scale characteristics of snowfall in the Sierra <br />Nevada have been studied at length by a number of organizations <br /> <br />11 <br />