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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reference to a likely radar seeding signature in the real time radar observations. This case, 19
February, has lead to a fairly comprehensive analysis of nearly all of the available data sets, and
appears to represent a \..-ell documented case of seeding effects in clouds above the plateau as well
as at the surface.

A. 26 January 1994 Case Study
1. Additional !\Ieteorological Observations
The evolution of cloud over the plateau was described in Section IlIA. Clouds were shallow
and SL \\' development was slight for much of the seeding period. Both MSU high altitude
generators \\'ere operated. The conditions at each site were similar and the data from H.t\S are shown
in Fig. 35. The third panel shows the SF" release rate. The AgI release actually ended about 1540.
The \\ind during the seeding period was consistently from about 2300 at 2 m S-l until 1350. From
1350 through the end of the AgI release, the wind veered to the west. then shifted to the west-
northwest at 1800. The temperature during seeding was -60to _50, and the seeding site was below
cloud base. The mobile radiometer data in the bottom panel of Fig. 35 suggest the best seeding
conditions were near the end of the seeding period when liquid occasionally exceeded 0.10 mm.
At plateau top the wind during seeding was more westerly than at either seeding site. At RRS
(Fig. 7) the \\ind direction varied between 265 o and 2800at a speed of about 4 m S-I. The temperature
at RRS was -9" to -80 and the site was in and out of cloud, with a few icing counts recorded before
and during seeding. At the center of the plateau the Doppler sounder detected winds (not sho\\<n)
from about 260" at 6-7 m S-l within 100 m of the surface, with veering to about 3000 at 400 m AGL
and a slight increase in speed to 8 m S-I. Above 400 m AGL the vvind veered sharply to a northerly
direction, and eventually to northeasterly directions near the end of the seeding period.
Data from the target site (TAR) are shown in Fig. 36. At TAR winds were more northerly
than at RRS. \\ith direction generally being from about 2850 at 5-6 m s -I during the seeding episode.
The \\ind data from the 1400 Ntt. Pleasant sounding are shO\'vn in Fig. 37, along \'vith the vertical
profiles of relative humidity, potential tempera~ure (8) and equivalent potential temperature (8J.
The sounding showed a moist layer located from 2200 to 4500 m, with \vind veering through this
layer from 230" to about 3300. A \\ind speed maximum of 8 m S.I existed at the top of the moist

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