WMOD00304 ‎(2)‎

• Project Name: CREST
• Title: Colorado River Enhanced Snowpack Test
• Date: 1/1/1982
• Weather Modification - Doc Type: Report

the other objectives. Production of
water and confirmation of the
resulting increases will help in
deciding on the best use and
distribution of the additional water
suppl i es.

Envi ronmental and soci al impacts, as
well as the reduction of any risks
associated with cloud seeding, will
be considered throughout the
demonstration. These factors will
influence the use of the technology,
and will help in the evaluation of
the results and beneffts of the CREST
program. The environmental effects

of increased snowpack, 1 f any, wi 11
be thoroughly studied as the
demonstration progresses. Suspension
criteria will be used and revised
during all phases of the program as a
safeguard against potential flooding,
avalanche or other hazards.

Public involvement and understanding
of the CREST program and its
Objectives are vital to the success
of the demonstration. Public
acceptance and support are important
to the realization of a fully
operational weather modification
program in the Colorado River Basin.

SEEDING WINTER STORMS

In the high country of the Colorado
River Basin, as in all other winter
storm areas, only an estimated 10
percent of the available moisture in
seasonal storms falls to the surface
as snow. The remaining moisture
stays in the atmosphere and disperses
without ever changing to snow or
rain. Cloud seeding can improve the
efficiency of the natural
precipitation ~rocess and, under
favorable conditions, increase
seasonal precipitation by 10 to 15
percent, or another 1 percent of the
available ~isture.

The principles involved in seeding
winter (orographic) clouds are
relatively simple. The flow of moist
air over mountain barriers produces
liquid water droplets through
condensation as the air is forced
into colder temperatures at higher
elevations. These droplets tend to
remain in the liquid sta~e without
freezing at temoeratures lower t~an
OOC (320F) because of the purity of
tne water and the absence of foreign
par:icles in the free at~osphere;
they are referred to as "supercooled
droplets" and the clouds they form

are called supercooled clouds. If
ice particles occur naturally, or are
introduced artifically into these
supercooled clouds, the ice particles
will grow at the expense of the
droplets, and begin to reach the
surface as snow.

If the concentration of natural ice
particles is too low for
precipitation to form and fallout to
occur, the ice particle concentration
can be increased through the use of
seeding material. The JOOst common
seeding agents are dry ice, which
causes ice crystals to form because
of its extremely cold temperature,
and silver iodide, which has a
physical structure similar to that of
natural ice crystals. Ice crystals
formed by seeding can convert JOOre
supercooled water to snow, and
thereby increase the "efficiency" of
the clouds.

The technology of modifying winter
cloud systems to increase mountain
snowpack has been developing over the
past 30 years. Evidence about the
potential for snowpack augmentation
in the high mountains of the Colordo
River Basin is largely based on
statistical data from past projects

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