WMOD00266

• Sponsor Name: NAWC
• Project Name: Gunnison Cloud Seeding Annual Report 2004
• Title: The Development, Conduct and Evaluation of a Cloud Seeding Program for the Gunnison River Basin, Colorado During the Winter of 2003-2004 Winter Season
• Prepared For: City and County of Gunnison
• Prepared By: Don A. Griffith, David P. Yorty, Mark E. Solak
• Date: 8/1/2004
• Weather Modification - Doc Type: Report

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3.0 OPERATIONS

The 2003-2004 winter season cloud seeding project for Gunnison County began on
November 15, 2003 and ended on April 15, 2004. A total of 20 storm periods were seeded
during all or portions of 31 days. Three storms were seeded in November, five in December,
three in January, five in February, two in March, and two in April. A cumulative 3,299 hours of
operation were conducted during the season, releasing 39,588 grams of silver iodide. Table 3-1
shows the dates and ground generator usage for the 20 storm events, and Table 3-2 shows
operation times for each of the CNG sites.

Precipitation was again somewhat below normal in most areas of western Colorado
during the 2003-2004 winter season, totaling about 80-100% of the normal amount across the
Gunnison County seeding target area. As of April 15, Gunnison Basin SNOTEL sites averaged
91 % of the normal water year precipitation, and only 78% of average snow water content. The
low snow water content was largely a result of warm weather in March that led to substantial
melting. The higher precipitation and snowpack amounts were generally in the southern portion
of the basin, particularly in the vicinity of the San Juan Range, where precipitation over the
season was close to normal.

The 2003-2004 season started out close to normal, except for a dry October (when rain or
melting snow usually occurs), which caused water year precipitation totals to start out below
normal. For this reason, water year precipitation totals and snow water content were very similar
throughout most of the season. Precipitation (snowfall) was very close to normal in November
and December. A series of heavy storms at the end of December and beginning of January
brought about 3-5" of water equivalent to most of the target area, bringing both water year
precipitation and snow water content to above average levels. The weather pattern was generally
dry during the remainder of January and most of February, causing water year precipitation (and
in some areas snow water content) to drop to somewhat less than average values. A series of
heavy storm events in the southwestern U.S. during late February brought as much as 5" of water
equivalent to portions of southwestern Colorado, particularly the San Juan Range, and brought

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