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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The linear regression equation developed from the hislOrical relationship between the
control and target groups, including McClure Pass as a target site. is as follows:

Yc= 1.12* Xo - 0.99

(I)

where Yc is the calculated average target precipitation (inches) and Xo is the average observed
control precipitation (inches) for the December-March period. This regression equation has a
correlation coefficient (r value) orO.87.

Similarly. the regression equation when ~1cClure Pass is excluded from the target group
is as follov.'s:

Yc~ 1.\3' Xo- 1.81

(2)

The r-value (correlation) for equation (2) is 0.83.

4.1 A Precipitation Evaluation Results

When the observed average control precipitation (7.14 inches) for the December, 2003
through March. 2004 period was insened in equation (l). the most probable average target area
precipitation was calculated to be 6.98 inches for all target sites (including McClure Pass). The
actual observed average precipitation for the six gages in the target group was 7.16 inches.
slightly more than that predicted.

The seeding effect (SE) can be expressed as the ratio (R) of the average observed target
area precipitation to the average calculated target area precipitation. such that.

SE ~ R ~ Yo/Yc

(3)

~o