WMOD00373

• Title: Investigations of Winter Storms in Utah
• Prepared By: Alexis B. Long, Atmospheric Sciences Center
• Date: 12/1/1986
• State: UT
• Weather Modification - Doc Type: Report

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will grow by vapor diffusion and by riming, at the expense of the

supercooled water in the cloud, and will fall through the cloud

with trajectories which carry them onto the mountain slopes. If

this hypothesis is true, the effect of the seeding is to increase

the amount of snow from the clouds and their resultant precipita-

tion effici,ency."

The hypothesis as stated here refers to the Tushar Mtns but, in fact, is

applied wherever there is seeding of winter clouds over mountains within

Utah. The hypothesis assumes there are supercooled liquid water regions

in the clouds, that seeding materials are delivered to these regions,

that additional ice crystals will be produced by the seeding, that they

wi 11 grow by diffusion and riming and consume the supercooled liquid

water, and that they will fall along trajectories terminating on the

mountain slopes. An evaluation of the Utah operational project, which

~s a purpose of the present research, must focus on the validity of

these assumptions. These assumptions formed the basis of the major

scientific objectives of the 1985 field research program listed in the
Introduction.

b. Seeditlg generator locations. Figure 2 shows the approximate

locations of th,e twelve ground-based silver iodide generators used ~n

1985. The generators were located in valleys around the mountains of

Washington County. The generators were manually operated by local resi-

dents on instructions from meteorologists of NAWC. Each generator

released 6 grams of silver iodide per hour.

c. Seeding decision methodology. . Seeding decisions of the opera-

tional project were based on a determination that clouds were

"seedable". Data for making this det,ermination came from National

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