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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resulting estimated data at some sites were very similar to the original snowcourse data. while
differences of 10-15% were found al some of the sites. The S1\OTEL observations \I..'ere higher
than the snowcourse observations at most target sites.

After careful consideration. NA we decided to use the ;"\,RCS estimated data in place of
the mixture of manual snowcourse and S~OTEL measurements. \Ve believe that using these
NRCS estimates can help eliminate any inherent systematic bias bet\\'een data obtained using the
snowcourse and S!':OTEL measurement systems.

April I snowpack readings have generally become accepted as the most representative
data set since they usually represent the maximum snow accumulation for the winter season in
most western mountain ranges. Most streamflow and reservoir storage forecasts are made on the
basis of the April I snowpack data.

4.2.1 Regression Equation Development

The procedure was essentially the same as was done for the precipitation evaluation. i.e..
control and target area sites .....ere selected. and average values for each were determined from the
historical snowpack data. The historical water years of 1971-76. 1978. 1983-84. 1986-92. and
1997-2000 were used in the snowpack (water equivalent) evaluation. a total of 20 seasons. The
2002.2003 evaluations (Griffith. et a1. 2003) used 22 seasons. They did not include the NRCS
sites of Crested Butte and Keystone. which had missing data during water years 2001-2003.
Observations resumed at these two sites for the 2004 v,,'ater year (2003-04 season). These sites
were therefore included in this analysis since they are located within the intended target area.
Four S~OTEL target area sites used in the precipitation anal)'Ses were also used in the snow
water content analyses (McClure Pass. Butte. Park Cone. and Porphyry Creek). The NOI1h Lost
Trail S!\OTEL site. which could not be used in the precipitation analysis due to a shan period of
record. was used in the snowpack analysis since an adequate snowcourse record was available at
that location. Two new sites. Lake City and Cochetopa Pass (both manual snow course sites).
were added to the target sites to represent the added program area on the south ponion of the

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