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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March precipitation at Bluff (which has had a stable location) and Cedar Point. Utah for the
period from 1958 through 2002. There is an apparent break in the plot that began in 1993.
Similar plots comparing Bluff with other stations did not demonstrate the break in the plot
observed in Fig. 4.3. As a consequence. consideration of Cedar Point as a control site was
dropped. even though the station records do not indicate change in location or equipment.

Colorado apparently did not have a high elevation precipitation storage gage observation
program similar to one in Utah lhal provided historical precipitation data prior to the
implementation of the S!\OTEL program. As a consequence. there arc limited historical records
of high elevation precipitation in Colorado. S!'\OTEL data became available in Colorado
beginning in 1981-82. There were historical seeding programs in the early 1980s and during the
waler years of 1993 through 1996 that may have impacted the precipitation in the target area.
These years ....'ere excluded from the analyses. There was one water year (1995) in which
seeding was conducted in a prime control area (Park Range). This year was also excluded from
the analyses. The resulting historical period selected. from \,,"hich the regression equations would
be developed. included the water years of 1983~1984. 1986-1992 and 1997-2002. a cumulative
IS-year period.

Implementation of the above control site selection criteria resulted in the selection
of approximately 20 stations for consideration as control precipitation sites for the 2002-2003
program (Griflilh. ct al. 2003). After ditTerent combinations of control sites were explored to
evaluate their degree of correlation. eleven control sites were finally selected. Figure 4.4 shows
the control (and target) site locations and Table 4-1 provides additional control site information.
These same control sites were used in the development of linear regression equations used in
evaluation of the 1003-2004 winter program.

4.1.2 Target Area Gage Sites

Relatively long term (15years) precipitation measurements were available from SIX sites
within the intended target area of the project (see Fig. 4.4 for site locations). Five of these sites
were used in the 2002':!003 evaluations. A sixth i\"RCS site. Slumgullion. was added to represent

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