WMOD00403

• Title: Special Regional Weather Modification Conference Augmentation of Winter Orographic Precipitation in the Western US
• Date: 11/11/1975
• Weather Modification - Doc Type: Report

SAN JUAN AND CLIMAX

Lawrence M. Hjermstad
EG&G, Inc., DUratlgo, Colorado

INrRODUCTION

In 1959 a randomized research seeding program for wintertime orographic storms over
the central Colorado Rockies was init:iated by Colorado State University. Using from
six to eight ground based silver iodide nuclei generators located upwind of the Free-
mont Pass - Climax, Colorado Target area, this research program has collected preci-
pitation and various cloud physics data over sixteen winter seasons. An analysis of
the seeded and natural precipitation data from the first five winter seasons indicated
that increases in precipitation from 100 to 200 percent occurred when cloud systems
with average 500 mb temperatures of _:Wo and warmer were seeded by the appropriate
project generators. Small changes in preci.pitation from -5 to +6 percent were indi-
o ' 0
cated when cloud systems with 500 mb temperatures of from -21 C to -26 C were seeded.
Decreases in precipitation around 22 to 46 percent were indicated when cloud systems
o
with 500 mb temperatures colder than ..26 C were seeded~ Nearly identical results were
indicated when the next four winter Sl~asons: seeded and natural precipitation datawere--
analyzed by the same statistical methods.

The promising indications from the Cl:lmax I'esearch program and other win~ertime
orographic seeding programs, along with an increasing demand for more water in the
western United States, prompted the Bureau of Reclamation's Division of Atmospheric
Water Resources Management in 1968 to contract with Colorado State University to
design a larger scale wintertime orographic. research cloud seeding program in the
Upper Colorado River Basin. This program 'ifl'Ould replicate the research results ob-
tained from the Climax program and another wintertime seeding program conducted by
Colorado State University over Wolf Creek Pass in the San Juan Mountains of south-
western Colorado. The ultimate goal of the Colorado River Basin Pilot Project was
to determine if the seeding of wintertime orographic cloud systems could assist in
meeting the mounting demand for additional water in many parts of our nation and
provide a sound evaluation of precipitation increases. Other purposes of the Pilot
Project were to:

1) produce positive incrE~ases in snowfall over a pre-selected 1300 square
mile Target area in the southeastern San Juan Mountains in southern Colorado and

2) provide for sound sciEmtific and economic evaluation of the applied
operation technology and the increased precipitation.

Late in 1969 two contractors, EG&G, Inc. and Western Scientific Services, Inc. began
installing a variety of meteorological, hydrological, and communications instrumen-
tation in and around the pre-selected Target area in the Southeastern San Juan Moun-
tains in southern Colorado as shown in Figure 1. The equipment and instrumentation
used on the Colorado River Basin Pilot: Project included:

15 remotely controlled cloud nuclei generators (NAWC type)
20 manually controlled cloud nuclei generators (EG&G type)
2 acoustical ice nuclei counters (NCAR type)
6 expansion ice nuclei counters (Bigg-Warner type)
2 RD-65 rawinsonde units for upper air soundings
1 central cont!,ol station and PDP-8 computer for data processing
5 radio repeaters
3 remote high altitude w€!ather stations (wind, temp, RH, precipitation)
7 remote weather stations: at selected generator sites (wind,temperature)
1 mountain top weather station (avalanche meteorological data)

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