WMOD00444

• Title: Evaluation of Idaho's 1992-1993 Winter Cloud Seeding Program
• Date: 10/1/1993
• Weather Modification - Doc Type: Report

None of the years shown on figure 1 were seeded, so only natural variability is being
displayed. Suppose, however, that the year 1965 had been seeded and the other 29 years had
not been seeded. In that case, one would naturally suspect that seeding at least partially
caused the unusually large 1965 departure. However, suppose that 1967 had been the only
seeded year. Then one would suspect that seeding had little if any effect. As a final example,
suppose that only 1989 had been seeded. Then one might suspect that seeding had decreased
the snowfall. The reader should note that the suspicions associated with each of these
examples do not constitute scientific proof.

On the other hand, humans base decisions every day on suspicions or beliefs rather than on
proof. Given the vast number of circumstances where scientific proof does not exist, a person
often has little choice. The field of medical care is full of such examples. So even a
suggestion of possible seeding effectiveness, or lack thereof, may interest those considering
future cloud seeding operations.

4. SPECIFIC IDAHO TARGET AREAS

The Idaho cloud seeding program actually involved three projects. The intended target areas
were located in the Boise River drainage area east of Boise, the upper Snake River drainage
area of eastern Idaho and extreme western Wyoming, and the Bear River drainage area of
southeastern Idaho. The upper Snake target is actually separated into two more-or-Iess
continuous areas. The first lies on the south side of the Montana-Idaho border. The second
"wraps around" the north and east sides of the Bear target. Because this second portion of
the upper Snake target borders the Bear target, they cannot realistically be separated.
Seeding in one project might easily affect the adjoining project.

Seeding operations commenced first for the Boise target with the initial seeding done on
December 16, 1992. The first seeding for the upper Snake took place on January 18, 1993,
and the first seeding for the Bear occurred on January 22, 1993. However, complete
networks of AgI seeding generators were not in operation for any of the three target areas
on the dates noted, but were operational in the Boise by late December, and in the other two
targets by about February 1. Seeding continued until April 24 in the Boise, April 30 in the
upper Snake, and April 13 in the Bear.

Not every storm was seeded. A set of seeding criteria was established by NAWe, and they
attempted to seed only those storm conditions that met their criteria. Because of the scarcity
of observations in mountainous terrain, NA we relied primarily on forecasts made by their
meteorologists in deciding when to seed.

Most attention will be focused on analyses of the Boise target for the following reasons. The
Boise target, which had the longest period of seeding, could be expected to have the strongest
seeding signal. Very good target-control relationships (highR-values) will be shown between

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