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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Abstract

This Final Report presents the first results ofthe Desert Research Institute's analysis of data
sets from the 1994 ~OA.A..-Ctah \\inter field program. The program is a cooperative research effort
bet\\"een the State of Ctah and the ~ational Oceanic and Atmospheric Administration within the
Atmospheric ~lodification Research Program, and is aimed at evaluating the weather modification
techniques currently used in the winter sno\\fall augmentation project conducted operationally by
the State of Utah. The problems addressed in the 1994 field program on the Wasatch Plateau of
central Ctah were: 1) the transport and dispersion of seeding material into clouds over the plateau~
2) the evolution of supercooled liquid water in winter storms atTected the plateau~ and 3) the
detection of the physical effects of seeding orographic clouds using silver iodide and liquid propane.
The DR! work focussed mainly on the latter 1\\'0 areas of research.
In addition to analysis of seeding experiments, this report presents summaries of the storms
which affected the \Vasatch Plateau be1\\'een 15 January and 15 March 1994. The synoptic
characteristics of five storm periods covering 11 separate days are described. The bulk of the cloud
seeding experiments were conducted during a period from 18 to 22 February, when a relatively cold
air mass had settled into the Great Basin. Distinct weather episodes were produced by a series of
short waves mo\'ing through the mean trough positioned over the western U.S. The \Vasatch Plateau
\"'as generally to the north of the jet stream in this situation, where winds were southwesterly to
westerly and relatively light. The temperature at the top of the plateau, near the 700 mb level, was
often colder than -8" C, and supercooled liquid water was consistently present in small amounts,
but over lengthy time periods. The winds, temperatures and liquid water conditions were frequently
conducive to seeding \\lth silver iodide.
The results from three case studies are presented. The first on 26 January 1994 demonstrates
a new technique for studying ground seeding plumes using tv\o'O mobile instrument platforms~ one
equipped with aerosol sampling equipment and a laser imaging probe, and the second a mobile
radiometer. The results of tandem passes through seeding plumes are described, vvith the main result
in this case being that supercooled liquid water was apparently not significantly depleted at the
position the plumes were intercepted a few kilometers downwind of the seeding generators.

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