WMOD00196

• Contract/Permit #: 2003-01
• Sponsor Name: Gunnison County, City of Gunnison, Crested Butte
• Project Name: WM Evaluation Report
• Title: The Development, Conduct and Evaluation of a Cloud Seeding Program for the Gunnison River Basin, CO During the 2003-04 Season
• Date: 8/1/2004
• County: Gunnison
• State: CO
• Weather Modification - Doc Type: Reports

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became routine, Before this system was 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 2003 NRCS data are considered provisional at the time this report is being prepared.
There are some concerns regarding SNOTEL 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 storm, Whether these factors
affect the target and control gages in the same fashion in any given winter season is debatable.

5.1.1 Control Area Precipitation Gage Sites

There have been, and continue to be, several cloud seeding programs conducted in the
State of Colorado. As a consequence, potential control areas that are unaffected by cloud
seeding are somewhat limited in geographic area. 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 part 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,
since the actual impact from cloud seeding on a season to season basis is difficult to quantify.

To further complicate the matter, the number of sites (especially snow course sites) is
continually being reduced. Even the cooperative observer sites, which are managed by the
National Weather Service, have either been discontinued or become inactive at several locations.

NA WC performed another evaluation of a new cloud seeding project conducted this past
winter in the Central Colorado Rockies and sponsored by Denver Water. One of the steps in the
development of a target/control evaluation of that project was a comprehensive search of all

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