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<br />. <br /> <br />e <br /> <br />, <br /> <br />e <br /> <br />., <br /> <br />bands, cells, or orographic clouds is shutoff from high levels. <br />Radar studies show regions of no radar reflectivity occurring <br />near cloudtop and progressing downward between bands. Frequently <br />the downward motion reaches the ground and produces a sharp <br />horizontal gradient of reflectivity on the back side of the <br />preceding band. <br /> <br />9. The bright band is a highly significant phenomena, parti- <br />cularly near the foothills. Radar returns in the bright band <br />occasionally reach 60 OBZ. <br /> <br />10. Vertical dispersion of seeding material is very 1 imited at <br />low levels in the Sierra Nevada. The frequent occurrence of the <br />low-level jet severely limits opportunities for releases below <br />5000 ft. Prestorm conditions, under which transport and <br />diffusion studies were conducted to simulate storm conditions, <br />showed very poor vertical dispersion of material and very rapid <br />horizontal transport of material parallel to the barrier. Stratified <br />tank model s imul ati ons conducted by the Bureau strongly resemb'] e <br />observed plumes. <br /> <br />11. Convergence zones in and near bands, as determined by <br />doppler radar, appear to occur on the front side of a band as it <br />approaches the foothills and on the back side as it continues up <br />the barrier. The transition from the front to the back is not <br />yet understood. <br /> <br />1-11 <br />