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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in the snowpack analysis were also obtained from the :o-;rRCS. When the ~'RCS. known then as
the Soil Conservation Service (SCS). introduced the S!'\OTEL data acquisition system in the late
1970's. access to precipitation and sno'Apack (water equivalent) data in mountainous locations
became routine. Before this system \vas developed. data had to be acquired by visiting the site to
make manual measurements (e.g.. snow surveys). which are still being done to the present time
at a few sites in the western United States.

The 2004 XRCS data are considered provisional at the time this report is being prepared.
There are some concerns regarding S1\OTEL observations of precipitation in higher elevations
during the wintertime. Precipitation normally occurs as snow at these elevations. often
accompanied by moderate or strong winds. Snow can build up around the top of the
precipitation standpipe storage gage. thereby reducing its catch and under-measuring
precipitation. Moderate to strong winds can cause the snow to blow past the top of the storage
gage. which also reduces its catch efficiency. These clogging and wind factors may be a
function of the density of the snow. which can vary from storm to stoml. Whether these factors
affect the target and control gages in the same fashion in any given winter season is debatable.
but if they do affect the areas differently. they constitute a source of noise in the data and would
decrease the accuracy of calculations based on them_

4.1.1 Control Area Precipitation Gage Sites

There have been. and continue to be. several cloud seeding prohTfams conducted in the
State of Colorado. As a consequence. potential control areas that are unaffected by cloud
seeding are somewhat limited. This is complicated by the fact that the best correlated control
sites are generally those closest to the target area. and most measurement sites in this pan of the
state have been subjected to "contamination'. by numerous historical and current seeding
programs. This renders such sites of questionable value for use as control sites

To further complicate the matter. the number of sites (especially snow course sites) is
continually being reduced. E\-en some cooperative observer sites. which are managed by the
National Weather Service. have either been discontinued or become inactive at sevcrallocations_

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