WMOD00458

• Project Name: Project Skywater
• Title: Generalized Criteria for Seeding Winter Orographic Clouds
• Date: 7/1/1977
• Weather Modification - Doc Type: Report

than an hour. If a large number of soundings is used in stable

orographic conditions, independence of the samples is sacrificed.

I f few soundings are used Wlder rapidly changing conditions, poor

classification of physical factors and an unnecessary reduction

in sample size occur. Several studies have been conducted on the

correlation of cloud variables derived from soundings taken in win-

ter orographic clouds during t~le Colorado River Basin Pilot Proj-

ect [4]. For soundings 3 hours apart in the San Juan Mountains,

correlation coefficients between soundings range near 0.70. For

soundings 6 hours apart the correlation coefficients are less than

0.50 and for soundings 9 hours apart correlation coefficients are

less than 0.30. Some projects had soundings every 2 hours while

others had soundings 3, 6, or 12 hours apart. The decision was

made to use soundings 6 hours apart to better classify cloud con-

ditions and yet avoid great correlation between observations.

Soundings less than 6 hours apart were not used. In addition to

the sounding data, precipitation gage data, seed/no-seed tabula-

tions, and descriptors of the individual barriers and seeding net-

works were used. Hourly gage data were used because cases could

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be selected on less than 24-hour intervals. Climax suffered in

this regard because most of its evaluation was done using snow-

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boards. However, a limited number of hourly gages was available.

Six-hour blocks of precipitation were accumulated for each sounding.

Precipitation from 2 hours before to 4 hours after a sounding was

averaged to give a 6-hour average precipitation rate.

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