WMOD00558

• Project Name: Project Skywater, Sierra Cooperative Pilot Project
• Title: Project Skywater, Sierra Cooperative Pilot Project - Fall 1984 Status Report
• Date: 12/1/1984
• Weather Modification - Doc Type: Report

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The principal tools for finding SLW in the earliest years of SCPP were

the optical probes on the cloud physics airplane. These probes recorded

sizes and concentrations of cloud and precipitation particles and gave

indications of whether they were solid or liquid. The aircraft

observations were compared to radar data to see if SLW could be

associa ted with particular precipi ta tion echo types, which could in

turn be related to particular stages in a storm's life-cycle.

The first few winters of exploration inside clouds over the ARB showed

SLW to be less than had been expected. The highest concentrations

of SLW by aircraft were found in cumulus clouds forming about 30 to

65 km upwind of the crest, that is, over the foothills, behind eastward

moving storms. The orographic clouds formed ahead of most storms and

the deep clouds within major storms were fotmd to have low concentrations

of SLW and an abundance of natural ice crystals, so they appeared not

to be good candidates for seeding. However, these aircraft observations

were not consistent with frequent observations of riming at the ground

and of rimed snowflakes above the snowline during many storms.

The scarcity of SLW at flight altitudes (restricted to at least 600 m

(2000 ft) above the highest terrain) within major storms led some SCPP

scientists to suspect that SLW was occurring very close to the ground

on windward slopes, where the airplanes could not sample. To test

this idea an icing rate meter and other instruments were installed

and operated continuously for two winters on top of Squaw Peak. Squaw

Peak is 2625 m (8,610 ft) high and forms part of the Sierra Nevada