WMOD00390

• Title: A Proposed Wintertime Weather Modification Research Program for Colorado
• Date: 1/1/1980
• State: CO
• Weather Modification - Doc Type: Report

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cloud seeding can be expected to increase the amount of precipita-
tion produced when: (1) there is an abundance of moisture in the
form of supercooled liquid welter; (2) there is a deficiency of
natural ice nuclei; (3) the air is slightly to moderately unstable;
and (4) the time required for growth and fallout of the precipita-
tion is within a range of wind speeds which allows it to fall into
the target area. The routinE! identification of the seedability
indices requires further deVE!lopment for practical field use. The
bounds for each of the neces~:ary criteria need to be refined con-
sidering the specific conditi.ons encountered in each area where
seeding operations are planned or are being conducted. The
refinement of the bounds for favorable seeding conditions requires
that atmospheric data be collected and analyzed in conjunction
with cloud seeding programs.
Present methods used to seed winter orographic clouds are
aircraft and ground-base arti.fical ice nucleus generators.
Aircraft provide a flexible TIleanS of seeding, allow the use of
either dry ice or artificial ice nuclei, and should result in
very accurate targeting of the seeding material. However, aircraft
seeding is considerably more expensive than ground-base seeding,
the portion of the orographic: clouds actually seeded is very
limited and there is a high probability of over-seeding if the
seeding material is released too near the target area. There
also exists severe operational flying restraints including air-
craft icing problems, bhe proximity of the flight path to moun-
tains, and scarcity of navigation aids near the mountain areas
to be seeded.
Up to the present time, the most prevalent mode of seeding
orograhic clouds has been the use of a network of artificial
ice nucleus generators on the ground located upwind of the
mountain barrier. Turbulence associated with wind flow has been
relied upon to disperse the nuclei throughout the clouds over the
target area. However, target:ing uncertainties exist with ground-
based seeding due to a combination of atmospheric stability and
wind variation with height. Large mountain barriers distort the
flow of air, even to the point of forcing the low-level wind to

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