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 DENVER WATER DEPARTMENT CLOUD SEEDING PROGRAM

November 2002 started out with a continuation ofthe wet weather trend started during the second half of October.
Five weather systems over fifteen calendar days continued to maintain the above normal snowpack left by
Octobers weather systems. Early indications were that this winter might be near or slightly above normal for
snowpack and precipitation and allowed for earlier openings for most of the ski areas in Colorado.

The trend of frequent weather systems moving through the Western U.S. increased through December bringing
with it the occurrence of eight seeding opportunities over 23 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 Central Mountains had decreased to an average slightly under normal with several monitoring sites in the
Seeding Area continuing to have above normal readings. ".

The gradual drying trend of the weather system continued throughout January with shorter storm duration's for
seeding operations. Eight seeding opportunities occurred over 16 days in January. At the end of January, the high
country snow pack in the Central Mountains had dropped to near 80% of normal. Most of the Seeded Area
monitoring sites still indicating an additional 15% greater snowpack and precipitation

Above normal precipitation and frequent weather systems with good seeding potential returned to the Central and
Northern Colorado Mountains during February with 9 weather systems and 21 operational seeding days.
February's snowpack increased so rapidly in the last half of February that an avalanche warning was issued. The
average precipitation for the region had increased to about 90% of normal with many monitoring sites in the
Seeded Areas indicating 10 to 15% more precipitation than adjacent unseeded sites.

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 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. 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 27th of March. Several avalanche
warnings were issued for the Northern, Central and the East-slope Mountain Ranges in Colorado during these
weather events suspending some seeding activities mainly in the Northern and Eastern portions of the Seeded
Area. At the end of March, the snowpack and precipitation in the Colorado Central Mountains had returned to just
under normal with most monitoring sites in the seeded area indicating 8 to 15 % above normal precipitation for the
season.

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 ftrst 7 to 10 days of April,
2003. This request was approved by the State and the seeding operations were continued on five of the first seven
days of April, 2003.

The DWD Operational Seeding Summary is presented in two parts. The first summary of seeding events is for the
main DWD Program Area. This Summary indicates the dates of aU 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, the number of
generators shared with the Upper Arkansas Program and the Total Output of Silver Iodide for each operation for