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<br />e <br /> <br />e <br /> <br />- <br /> <br />.. <br /> <br />an average direction of 1800. The average speed was 28 mls with a range <br />from 11 to 57 m/s. The low-level jet intensified with the approach of <br /> <br />the front and of individual bands and appeared to feed moisture into the <br />southeast side of bands and frontal clouds. <br /> <br />8. Strong subsidence occurred between stronger bands. As bands crossed <br />the Sacramento-San Joaquin Valley, pre~cipitation from preceding bands, <br /> <br />cells, or orographic clouds stopped. Radar studies showed radar echoes <br /> <br />disappearing near cloud top and then progressing downward between bands. <br />Frequently, the downward motion reached the ground and produced a sharp <br />horizontal gradient of reflectivity on the backside of the preceding <br /> <br />band. <br /> <br />9. The bright band was a highly significant phenomenon, particularly <br /> <br />near the foothills. <br /> <br />Radar returns in the bri ght band occasionally <br /> <br />reached 60 dBZ. <br /> <br />10. Vertical dispersion of seeding material was very limited at low <br />levels in the Sierra Nevada. The frequent occurrence of the low-level <br /> <br />jet severely limits opportunities for releases below 1525 m (5000 ft). <br /> <br />Prestorm conditions, under which transport and diffusion studies were <br />conducted to simulate storm conditions, showed very poor vertical <br /> <br />dispersion of material and very rapid horizontal transport of material <br />parallel to the barrier. Stratified tank model simulations conducted by <br />the Bureau strongly resembled observed plumes. <br /> <br />11.' Convergence zones in and near bands, as determined by Doppler <br /> <br />,. <br />radar, appe~red to occur on the front side of a band as it approached <br /> <br />the foothills, and on the backside ,as it continued up the barrier. <br /> <br />1-5 <br />