Weather Mod Critical Issues Report

• Project Type: General OWC
• Project Name: Weather Modification
• Title: Critical Issues in Weather Modification Research
• Date: 1/1/2004
• Water Conservation - Doc Type: Final Report

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(1986), Such suggestions from exploratory analyses should not be considered absolute
proof by themselves. However, these particular experiments used high elevation Agl
generators, a seeding approach which has been shown to routinely result in transport and
dispersion of Agl plumes into the SL W zone, Moreover, both experiments have
considerable supporting physical evidence in agreement with the statistical suggestions.
Some physical evidence was collected during the BRE (Super, 1974; Super and
Heimbach, 1983) and some later by cloud physics aircraft (Super and Heimbach, 1988).
Convincing physical evidence, based on trace chemistry analysis of snowfall, was
reported for the Lake Almanor target well after the randomized experiment, as reported
by Chai et al. (1993) and Warburton et al. (1995a,b). The results of Warburton et al.
(1995a) are in particularly good agreement with earlier statistical suggestions of seeding
success with cold westerly flow, and further demonstrated that failure to produce positive
statistical results with southerly flow cases was likely related to seeding affecting control
stations (mis-targeting). Both experiments had evidence suggesting that the
condensation-freezing mechanism resulted in the formation of high seeding crystal
concentrations just downwind of the generators. This mechanism (Finnegan and Pitter,
1988) was not understood at the time of the experiments, but may have been a major
factor in their promising results when AgI was released directly in-cloud at temperatures
less than _60C. Both experiments had evidence of the largest increases in snowfall within
about 12 miles ofthe generators, and for colder cloud temperatures. The panel is
unaware of other winter orographic randomized experiments from the western U.S. that
have both strong statistical suggestions and considerable physical evidence to support
those suggestions. According to the review by Reynolds (1988), only the Bridger Range
Experiment had such dual evidence at that time.

These two randomized experiments strongly suggest that higher elevation seeding
in mountainous terrain can produce meaningful seasonal snowfall increases. These
suggestions are based on both statistical and physical evidence, Although the
experiments were run decades ago, they are still worth reviewing in the absence of more
or equally impressive results from the limited number of more recent randomized winter
orographic cloud seeding experiments.

The studies of Warburton and Wetzel (1992), Warburton, et al. (1995a), and
Super and Holroyd (1997) are pertinent. The Warburton and Wetzel paper showed how
8mm wavelength radar was used in conjunction with microwave radiometer
measurements for assessing snowfall augmentation potential. The second paper reported
on studies in Lake Almanor regarding the targeting and tracking of silver iodide in the
precipitation which demonstrated that the transport and dispersion problems are
significant and can lead to a much weakened capability of detecting seeding effects by
precipitation statistics, The work of Super and Holroyd showed marked increases in ice
particle concentrations produced by cloud seeding in Utah.

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