CWCB Wintertime Weather Mod Report

• Project Type: General OWC
• Applicant: Weather Modificaton
• Project Name: Colorado Weather Modification Program
• Title: CWCB Wintertime Weather Modification Report Fall 2002 - Spring 2003
• Date: 7/1/2003
• Water Conservation - Doc Type: Final Report

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SUMMARY OF WEATHER AND OPERATIONAL SEEDING OPPORTUNITIES FOR THE
2002-2003 SEASON OF THE UPPER SAN MIGUEL DRAINAGE BASIN CLOUD SEEDING PROGRAM

November 2002 started out with a continuation of the wet weather trend started during the second half of October.
However, after November 11th a "dry spell" set in until the last day of November. This change in the precipitation
pattern resulted in seeding operations for only four weather systems over eight calendar days. Early ,indications
were that this winter might be near or slightly above normal for snowpack and precipitation began to wane with
this shift in the weather pattern. The early season snowfall allowed for earlier openings for most of the ski areas in
Colorado, however the Northern Mountains of Colorado were being favored by the current weather patterns.

The trend of frequent weather systems moving through the Western U. S. increased through December bringing
with it the occurrence of six seeding opportunities over 15 calendar days into January 1,2003. A subtle change
was becoming apparent with these systems. The intensity and duration of each system was becoming slightly less
as there was less southwesterly wind to bring in large amounts of moisture and most of the precipitation with these
systems was occurring mainly in the higher elevations of the mountains. By the end of December, the snow pack
in the San Juan Mountains had decreased to an average of90% of normal with several monitoring sites in the
Seeding Area continuing to have slightly above normal readings.

The drying trend of the weather systems continued throughout the first half of January with shorter storm
duration's for seeding operations. The second half of January 2003 had no weather at all to work with as any
weather moving into Colorado brought in precipitation only to the Northern Mountains or the North slopes of the
San Juan Mountains. Only four.seeding opportunities occurring over 8 days was the final tally in January. Atthe
end of January, the high country snow pack in the San Juan Mountains had dropped to near. 70% of normal. Most
of the Seeded Area monitoring sites still indicating about 80 % of normal precipitation.

The Seeding Program over the Pine River Drainage ended on January 20, 2003.

The San Juan Water Commission of Farmington, New Mexico contracted with Western Weather Consultants, LLC
to extend the Seeding Program over the entire Upper Animas and La Plata River Basins to the end of this season's
seeding efforts on April 7, 2003.

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The Seeding Programs over the Dolores and Upper San Miguel River Basins and the Telluride Ski area ended on
February 14, 2003.

The wet weather trend continued into early March and then quickly turned very dry with warming temperatures.
A very large slow-moving weather system moved into Colorado from the Southern California region in mid March
and produced nearly continuous precipitation in the mountains of Colorado for about six days. This one system
produced nearly half of the normal annual snowpack for the Eastern Slopes of Colorado and added about 10 to
15% to the snowpack in the Central Rocky Mountain Region but only kept up with normal precipitation in the San
Juan Mountains. A second weather system moved into Colorado from the northwest a few days later and
continued the mountain precipitation for another four days until the 27'h of March. Several avalanche warnings
were issued for most of the mountain areas in Colorado during these weather events suspending some seeding
activities for a couple of days in the Seeded Area. At the end of March, the snowpack and precipitation in the San