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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rejected due to poor data quality which usually manifests itself in missing data. Fortunately.
missing data (typically on a daily basis) are noted in the historical data base so that sites can be
dropped from consideration if they have much missing data. We normally drop a site if it has
more than 2 or 3 days of missing data in a month for 4 or 5 months during the historical period
we are considering. which could be a 15-30 year period. While data quality may appear to be
satisfactory. another consideration is whether the station has been moved during its history. If a
significant move (more than a mile or change in elevation of 100-200 feet) is indicated in the
station records. then we may perform a double mass analysis of the station of interest versus
another station in the vicinity with good records. The double mass plot (an engineering tool) will
indicate any changes in relationships between pairs of stations. If these changes (changes in
slope of the line connecting the points) are coincident with station moves and they suggest a
significant difference in the relationship. the site is dropped from further consideration. Figure
4.3 provides an example ofa double mass plot comparing the accumulated December through

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Figure 4.3 Double-:\Iass plot comparing Bluff and Cedar Poinl. UT

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