WMOD00196

• Contract/Permit #: 2003-01
• Sponsor Name: Gunnison County, City of Gunnison, Crested Butte
• Project Name: WM Evaluation Report
• Title: The Development, Conduct and Evaluation of a Cloud Seeding Program for the Gunnison River Basin, CO During the 2003-04 Season
• Date: 8/1/2004
• County: Gunnison
• State: CO
• Weather Modification - Doc Type: Reports

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Grand Mesa. However, we were reluctant to exclude this site entirely, due to its significant
contribution to the historical regression equation, and the better target/control correlation which
could be obtained by including this SNOTEL site. Therefore, we decided to show two different
results in both the precipitation and snowpack analyses, corresponding to regression equations
which include/exclude this target site.

Experience has shown that it is virtually impossible to provide an accurate assessment of
the effectiveness of cloud seeding over one or two winter-spring seasons. However, as the data
sample size increases, it becomes possible to provide at least a qualitative answer to the question
of, "How effective was the seeding?" Since this past winter season represents the first seeded
season, only general indications of the success of the seeding would be expected at best.

Using the target-control comparison described above, mathematical relationships for the
variables (both precipitation and snowpack) were determined between a group of sites in the
unseeded (control) areas and the sites in the seeded (target) area. From these data, predictor
equations were developed, where the average value of the variable observed in the unseeded
(control) areas was used to predict the average value of the variable in the seeded (target) area in
the absence of seeding. A positive difference between the observed amount and the predicted
amount in the seeded area (target) during seeded periods may indicate a positive result of
seeding. A negative difference may indicate that the seeding decreased the precipitation (an
unlikely occurrence) or that the regression equation did not have a high enough correlation to
provide an accurate prediction.

5.1 Precipitation Analysis

Precipitation data used in the analysis were obtained from the Natural Resources
Conservation Service (NRCS) and/or from the National Climatic Data Center, and represent the
official published records of those organizations. Similar snowpack (water content) records used
in the snowpack analysis were also obtained from the NRCS. When the NRCS, known then as
the Soil Conservation Service (SCS), introduced the SNOTEL data acquisition system in the late
1970's, access to precipitation and snowpack (water equivalent) data in mountainous locations

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