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<br />002490 <br /> <br />Cold westerly storms are moderately convective with strong orographic <br />clouds on west-facing slopes. They will respond most favorably <br />to light to moderate seeding rates. The principal effect will be <br />increased efficiency and corresponding increases in total precipi- <br />tation along the upper slopes. <br /> <br />When the fact that the southerly type of storm produces by far the <br />largest proportion of precipitation is combined with the fact that <br />the maximum precipitation accumulation occurs slightly below the <br />average snowline elevation, MBA concluded that a large potential <br />for adding atmospheric water to the snowpack lies in redistributing <br />precipitation to a higher elevation. <br /> <br />Hypotheses <br /> <br />MBA developed hypotheses for the SCPP from the classification <br />of the storms into the two classes and recommended that the pilot <br />project attempt to modify the two storm types with separate objec- <br />tives. The orographic (westerly) storms should be seeded to <br />increase the efficiency of the storm, thus augmenting the amount <br />of precipitation resulting from these systems. The procedure <br />would be to seed the storms at light seeding rates to avoid over- <br />seeding. Seeding would be done with surface seeding generators and, <br />under certain circumstances, with airborne seeding generators. <br /> <br />i <br />I <br />i <br />, <br />I <br /> <br />It was recommended that the convective storms (southerly) be seeded <br />to increase precipitation at higher, colder elevations, primarily <br />through redistribution, providing a greater total precipitation for <br />storage in the snowpack. These storms would be seeded heavily, <br />with the object of altering the distribution of precipitation <br />with respect to altitude, thus increasing the snowpack. In addi~ <br />tion to seeding, the general orographic background of these storms <br />by surface generators, the pilot program would seed the updraft <br />areas of the imbedded convective cells heavily with high-output <br />airborne generators. <br /> <br />I <br />r <br /> <br />MBA suggested that the specific statement of the hypotheses to be <br />tested in the experiment will be: <br /> <br />(1) Seeding will increase the average precipitation on <br />treated sample events as compared to the untreated events. <br /> <br />(2) Seeding will increase the average elevation of maximum <br />precipitation on treated sample events as compared to <br />untreated events. <br /> <br />(3) Seeding will increase the average duration of precipitation <br />and/or the rate of precipitation on treated sample events as <br />compared to the untreated events. <br /> <br />15 <br />