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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somewhat before the ice nuclei plume arrived. This suggests the plume was sheared in the vertical
with the portion near the surface being offset to the north or south of TAR for most of the
experiment. The characteristics of the flow near the surface are somewhat unknown, and forcing
by local terrain features might also act to carry the plume away from the TAR site. One such feature
is the north-south oriented canyon just up\vind ofT AR {visible in Fig. 1 and matching the north-
south section of Highway 264 in Fig. 43J which slopes to the south into Electric Lake. In a stable
enyironment aerosols might be trapped in this canyon, and forced to move with the canyon
orientation, possibly affected by drainage flow. The Clark Model (Heimbach and Hall, 1994) with
high terrain resolution \\:ould be quite useful in analyzing this problem.

4. Summary of 26 Januar}' Case
This case served mainly as a demonstration of the usefulness of combining data sets from
mobile surface instrumentation. The storm had some seeding potential, \..-ith small amounts of SL W
observed during the seeding period. The temperature structure was such that AgI aerosols should
have been active as ice nuclei in the cloud region where seeding material was detected. Although
one atmospheric sounding showed a slight amount of convective instability, the seeding aerosol
plumes were not lifted more than about 250 m above the top of the Wasatch Plateau. The plume
from one of two generators was well documented as it reached the top of the Plateau by surface
instruments, but detection at aircraft altitude was rare.
Seeding effects are yet to be documented in this experiment. The careful documentation of
seeding plume locations at the surface allowed mobile radiometer data to be stratified according to
being in-plume or out-of-plume. The SL W depths measured in-plume on individual interceptions
at times appeared to be depleted, c~mpared to depths on either side of the plume, but overall the in-
plume SL \V average depth was not significantly different from out-of-plume depths. The radar data
showed the evolution of the natural cloud precipitation quite well, but seeding effects, if they
occurred, \Vere masked by the rather strong returns from the natural precipitation. Only the very end
of the seeding experiment was characterized by ,weaker radar echo and higher SL W amounts, and
may have some potential for revealing seeding effects under more detailed analysis. The best chance
for detecting seeding effects rests in the 2D probe data from the Starship and the target site, and this

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