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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The second criterion excludes very warm storms and those with cloud

bases above the crest level.

In these cases ice nuclei released from

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ground-based generators would not likely be mixed high enough to reach

the -5C level and thus would be ineffective.

The third criterion excludes those clouds in which the additional

l.ce crystals produced by seeding would be carried downwind beyond the

targeted mountain slopes and evaporate. In the Utah operational project

redistribution of precipitation to the downwind slopes is acceptable,

amd the only time this criterion ~s important is when there may be a net

loss of precipitation due to evaporation. The wind speeds required in

order to avoid evaporation are a function of the locations of the ground

generators relative to the mountain range, cloud base height, the depth

of the cloud, and the height and width of the mountain range onto which

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snow should fall.

Actual wind speeds normal to the range are compared

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to these required wind speeds.

The above criteria refer to stable or neutral periods of winter

mountain storm systems. Within winter storm systems there may also be

unstable periods when convection is dominant. Specific seeding criteria

for these conditions have not been developed and adopted in the Utah

project. When unstable conditions occur the criteria for stable or

n.eutral conditions are followed in the seeding decision-making process.

d. Procedures for simultaneous conduct of the 1985 operational

cloud seeding project and the 1985 field research program. it is clear

that the, above operational seeding criteria exclude some fraction of the

entire population of wintertime clouds over the mountains of Utah. It

is equally clear that it is only with the remaining clouds meeting the

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