WMOD00512

• Title: Special Report to the Commissioner - Precipitation Management for the Colorado River Basin
• Date: 1/1/1980
• State: CO
• Country: United States
• Weather Modification - Doc Type: Report

separately and the results indicated a 9-percent precipitation
increase for Climax I (251 cases) and a 39-percent increase for
Climax II (29 cases). Results from this experiment established
the relationship of cloud-top temperature with both positive and
negative seeding effects.

Subsequent analyses conducted by Colorado State University revealed
some evidence that the distribution of meteorological events between
seeded and nonseeded events was not random. A possible bias was
found in that seeded days tended to be naturally wetter than
nonseeded days. However. further analyses have shown that statistical
tests utilizing control station precipitation substantiate earlier
results.

Wolf Creek Pass Experiment

The Wolf Creek Pass experiment was essentially an operational
snowfall augmentation program conducted by Colorado State University
for the State of Colorado from 1964 to 1970. The target area was
the Wolf Creek fass region of the San Juan Mountains in south-
western Colorado. The basic design consisted of a yearly
randomization with 24-hour experimental units which were selected
on the basis of precipitation falling at one or more of the
sampling stations on Wolf Creek Pass or at a control station.
Seeding was conducted using ground-based silver-iodide/acetone
generators placed at varying distances from the target area.

The evaluation compared precipitation measurements from the summit
of Wolf Creek Pass with seven National Weather Service control
stations. The statistical methods were identical to those used
for the Climax experiments. The results indicated an increase of
52 percent with 441 cases. Rangno~/ has recently examined these
results and believes the meteorological conditions that occurred
during the nonseeded seasons brought unusually light precipitation
to the entire Four Corners area of the western United States. This
apparent bias could have resulted in a high ratio of seeded to
nonseeded precipitation in the target area. Rangno also believes
that this pattern exhibited itself in other watersheds with
similar exposures in the area. A reanalysis of this experiment,
incorporating control station precipitation. is planned.

Colorado River Basin Pilot Proiect

The Colorado River Basin Pilot Project was a 5-year Skywater program
(1970-75) conducted by the Water and Power Resources Service to test
the physical concepts for weather modification and their opera-
tional potential. The project target area was the San Juan

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