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<br />(b). Physical observations and statistical results <br />complement each other when incorporated into a randomized <br />experiment. <br />(c). The seeding hypothesis should be complete and <br />testable in so far as possible, so that even negative results <br />lead to advances in understanding. <br />(d). There is apparently considerable variability among <br />different locations in the Colorado Rockies. Riming was <br />apparently important in the San Juans but not at Climax, and <br />the Climax model did not work when direct transfer to the San <br />Juans was attempted. There may be differences in the <br />frequency with which stable orographic clouds are present in <br />the San Juans (where blocking flow is common) vs other areas <br />(where the upwind valley is not so extensive and not so U <br />shaped) . <br />(e). The null result from the CRBPP is a troublesome <br />indicator for seedability in the Colorado River Basin, and <br />needs explanation. There is little evidence that seedable <br />cases were missed (unless via suspension for too cold 500 mb <br />temperature), so the failure to achieve significant positive <br />results must indicate either that effects are small or that <br />some negative effects occur. <br />(f). The unstable storm stage in the CRBPP bears some <br />resemblance to the "shallow orographic" clouds from other <br />areas, except in its instability. The relatively low cloud <br />tops lead to temperatures warmer than in other storm stages, <br />and the cloud appearance is similar to that of an orographic <br />cloud because of the strong capping at cloud top. However, <br />liquid water contents are much higher, exceeding 1 g/m3, <br />because of the greater lifting in the unstable layer. This <br />cloud type appears to be the best CRBPP-area candidate for <br />seeding, and one for which a complete seeding hypothesis <br />(including delivery of seeding material, transport of <br />precipitation to the target, and production of significant <br />precipitation) can be formulated. Airflow and microphysical <br />models are needed to evaluate the feasibility of this seeding <br />candidate, because the crude calculations (Cooper and <br />Saunders), Although the crude calculations of Cooper and <br />Saunders (1980) suggest that there are possible precipitation <br />trajectories from the liquid water region ahead of the <br />mountain to the target area, those results are too uncertain <br />to provide a good basis for a seeding hypothesis. Airflow <br />and microphysical models are needed to evaluate the <br />feasibility of this seeding candidate. <br /> <br />14 <br />