WMOD00591

• Title: Investigations of Winter Storms over the Wasatch Plateau during the 1994 NOAA-Utah Field Research Program - Final Report
• Date: 7/1/1996
• State: UT
• Weather Modification - Doc Type: Report

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I. I~TRODlTTIO~

\Vater shonages in the western United States have prompted state and private agencies to
seek alternatives to increasing water supplies for agriculture, power generation and municipal use.
The states of~evada and Utah have conducted operational cloud seeding programs for the purpose
of increasing \\inter sno\\-packs for many years. The goal in these programs is primarily to increase
stream flow in the spring and summer for municipal and agricultural use. Recreation and wildlife
also potentially benefit from the additional water. The benefits of these projects depend a great deal
on the cost of the operations, which must be compared to the amount of additional snowtall that can
be produced by cloud seeding operations, and the dollar value of that additional water.
Although some statistical studies of the effects of cloud seeding in the 1960's and 1970's
indicated promising positive results from seeding winter storms, the physical basis for the apparent
effects was not completely documented. Carefully controlled experiments in several mountainous
regions of the \Vest in the 1980' s began to piece together the physical" chain of events" that occurred
after seeding orographically enhanced cloud systems. Among these studies were results reported by
Super and Heimbach (1988), Super and Boe l1988) and Deshler et al. (1988), for mountainous
regions of Montana, Colorado and California, respectively. All found evidence of microphysical
changes, ~-pically ice panicle concentration increases, from seeding orographic clouds with silver
iodide. In some instances the link to increases in precipitation at the ground was made, but these
cases were fe\\' in number.
In 1983 the state of Utah, along with the state of Nevada, began conducting research on
winter storm modification as part of a cooperative program vvith the National Oceanic and
Atmospheric Administration (NOAA). ~ear the beginning of the Utah program, the scientific
objectives were defined to be:
I} TO describe the spatial and temporal distributions of supercooled liquid water (SLW) in
l'dnter clouds over Utah's mountains, and the factors controlling the SLW;
2) to understand haw silver wdlde cloud seeding material may be deltvered from ground
generaTOrs to the "rimer cloud regwns containing SLW;
3) TO gain a better understanding of the physical processes responsible for winter

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