WMOD00011

• Applicant: Don Griffith North American Weather Consultants, Inc.
• Sponsor Name: City and County of Gunnison
• Project Name: Cloud Seeding Evaluation
• Title: The Development, Conduct and Evaluation of a Cloud Seeding Program for the Gunnison River Basin, Colorado During the 2003-2004 Season
• Prepared For: City and County of Gunnison
• Prepared By: North American Weather Consultants
• Date: 8/1/2004
• County: Gunnison
• Weather Modification - Doc Type: Report

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snow water con lent and precipitation back to above average in portions of the target area.
However. the northern and central portions of the Gunnison River Basin received less
precipitation. As a consequence. water year precipitation (and in some cases snow \'..ater
coment) remained below a\"erage. Then. an unusually \\'ann, dry March resulted in a substantial
amount of sno.....melt for so early in the season. mehing as much as half or more of the snowpack
below about the 9.500-ft level. A couple of storms in early April added to the snowpack.
although both snow waler content and water year precipitation remained below normal as of
April 15. the end of the seeded season. Figures 3.1 to 3.3 show snow water content and
precipitation. and nannals. at three S~OTEl sites for the 2003-2004 winter season. It can be
observed from these figures that the precipitation, and in two cases, snov,:pack water content,
increased by 3"-5" during the first two weeks of April. It turned out that the most seeding on any
storm during the winter occurred on the April 9.10 storm.

3,1 Opt'ralional Proct'durt's

In operational practice, an approaching storm was monitored at the NA we operations
center in Salt lake City, utilizing online weather information. If the storm met the seedability
criteria presented in Table 2.1. and ifno seeding curtailments or suspensions \\'cre in efTect, an
appropriate array of seeding generators was ignited and adjusted as conditions required. Seeding
continued as long as conditions were favorable and precipitating clouds remained over the target
area. In a normal sequence of events, certain generators \\.'ould be used in the early period of
storm passage. some of which might be turned ofT as the wind direction changed. with other
generators then used to target the area in response to the evolving wind pattern. Thc wind
direction during productivc storm periods in Gunnison County usually favors a westerly or
southwesterly direction, so that the generator sites on the wesUsouthwest side of the target areas
were used most often.

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