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

Juan Mountains had maintained the 80% of normal with most monitoring sites in the seeded area still indicating 8
to 15 % more precipitation for the season.

The Seeding Program in the Eastern San Juan's over the Upper San Juan and Piedra River Basins ended on March
i 7,2003.

A request was made the end of March 2003 to the Director of the Colorado Water Conservation Board to grant a
one-time ten-day extension of the Seeding Permit for this Program. This would allow the Program to seed a series
of weather systems expected to affect Colorado's mountain precipitation during the fll"St 7 to 10 days of April,
2003. This request was approved by the State and the seeding operations were continued on four of the first seven
days of April 2003. All in all, the winter turned out to be a "normal~ drier than average winter. The remaining
concern is that this winter followed a record dry winter of 200 1-02 and too many previous drier than normal
winters. .

The Western San Juan Operational Seeding Summary indicates the dates of all of this season's seeding operations,
the number of and total seeding hours of the generators in the network that were used to seed the Program Area,
and the Total Output of Silver Iodide for each operation.

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An analysis of the Season's Precipitation Data was completed using the Snotel Precipitation Sites in the San Juan
Mountains in and near the Seeding Programs. A Table of Results is included for all of the Seeding Programs in
this region, which also indicates seeding increases in your Program region and adjacent areas. Data provided in
this table includes:

I) The normal precipitation amount for this period of time (Nov. 1,2002 through Apr. 7, 2003) or for the
period of the seeding operations.
2) The actual precipitation observed for this period and its percentage of NormaL
3) The amount of precipitation that occurred during the seeding events as a percent of this seasons total.
4) The estimated amount of precipitation that would have occurred without a Seeding Program.
5) The estimated increase in precipitation as a percentage of the amount during the seeded period.
6) The estimated increase in precipitation as a percentage of the amount for the entire season.

The estimated increases in precipitation at each of the Snotel Sites in the region of the San Juan Mountains Seeding
Program Area was plotted on a map of the Snotel Sites in Southern Colorado. An analysis of the estimated seeding
results is included in included as a part of this report. Each of the Program participants may want to overlay this
data analysis on the precipitation collection watersheds benefiting their interest in the Program Areas and retine
thcir estill1llte af the tatal aaElitiel1ll1 aore feet ef sfla'.vpaok vlftter a','ailable fer nmeff resti!ting frem the elaud
seeding efforts.

Western Weather did some approximate calculations for each of the Program Areas. Using this analysis and
estimating a seeded area of about 35 Sq. Mi. in the Upper La Plata Basis with an average increase of 0.75" of
precipitation, one calculates an additional 1,400 Ac Ft of potential runoff from the La Plata Drainage Basin. A
similar calculation using approximately 90 Sq. Mi. in the Upper Florida Basin with an average increase of 1.00" of
precipitation, the calculation produces an additional 4,800 Ac Ft of potential runoff from the Florida Drainage
Basin. Using a seeded area of approximating 650 Sq. Mi. in the Animas Basin with an average increase of 1.35~of
precipitation, one calculates an additional 46,800 Ac. Ft of potential runoff from the Animas Basin. The seeded
area above Vallecito Reservoir is approximately 300 Sq. Mi. and had an average precipitation increase of 1.0"
producing a potential 16,000 Ac. Pt of runoff. The Upper San Juan and Piedra Basins are each about 280 Sq.
Miles. The average precipitation increase for the San Juan Basin was 1.5" and the Piedra Basin was 1.4"
producing 24,400 Ac. PI. for the Upper San Juan and 20,900 Ac. Ft of potential runoff for the Piedra Basin. . In
the San Miguel Basin, about 8,000 Ac. Ft. of potential runoff was produced over a 200 Sq. Mi. seeded area with an
estimated 0.75" increase in precipitation. In the Dolores Basin, about 15,000 Ac. Pt of potential runoff was
produced over a 400 Sq. Mi. seeded area with an estimated 0.70" increase in precipitation.

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