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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precipitanon development m natural and seeded orographic clouds; and
~) to gain a better understanding of the trajectories of natural and seeded precipitation
parricles m It"inter orographic clouds.
Since 1991 the o"~erall goal of the NOA.A.-Ctah program has been to evaluate the methodology
employed in the Ctah operational cloud seeding program, and to provide guidelines for improving
the program based on results of carefully designed and conducted field research programs.
In the early Utah field studies in 1983 (Long, 1984), 1985 (Long, 1986) and 1987 (Huggins,
1990a) the research concentrated on the structure of winter storms, primarily studying the influences
on, and the development of supercooled liquid water (SL W) in storms. These studies verified the
occurrence of supercooled liquid water in nearly all winter storms that affected the research area
in southwestern Ctah. A detailed case study, reported on by Sassen et al. (1990) and Long et al
( 1990), also revealed the importance of mesoscale weather and local topography in the development
and spatial distribution of SL W. Super and Huggins (1993) summarized SL Wand precipitation
amounts from four KOA..-\-Utah \'vinter field programs, shO\'ving that storms of all sizes contained
SL \V, eyen the largest precipitation producers.
From 1989 through the present, the NOAA-Utah program has focussed more on objectives
2, 3, and 4. Also, the field project area was moved from the Tushar Mountains of southwestern Utah
to the Wasatch Plateau of central Utah. The Wasatch Plateau offered the benefit of more uniform
terrain, and thus the adyantage of conducting research aircraft tlights at much lower heights above
the terrain. In field programs in 1991 and 1994, the main effort was spent documenting the transport
and dispersion of cloud seeding aerosols over the Wasatch Plateau from valley and high altitude
ground-based seeding experiments. In addition, the spatial characteristics of SL W were investigated
using a mobile microwave radiometer, and the physical effects of seeding were studied using
ground-based mobile and stationary instrument platforms, and an instrumented research aircraft.
Results from these studies can be found in Super ( 1994), Super (1995), Huggins (1995), Holroyd
et al. (1995), Heimbach (1996), Huggins (1996), and Super (1996). The last four papers cover results
from the 1994 field program, including modeling studies which describe aerosol transport from both
high altitude and yalley-based seeding locations and documentation of microphysical and radar
seeding signatures.

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