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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(0700 - 1400) are shown in Fig. 9. The winds at RRS were relatively steady from a direction of
about 225". and ranged in speed from about 12 m s': at the beginning of the period to 6 m S-I by
1300, \\ith the average around 9 m sol. The temperature at RRS increased steadily from -70 at 0700
to -4" at 1400. Icing at RRS was at the rate of about 2 trips of the Rosemont probe per hour. The
USBR radiometer recorded SL W depths up to 1.2 mm, with values generally greater than 0.6 mm
through 1130. then gradually declining to less than 0.3 mm by 1400. Precipitation was light to
moderate, with graupel showers indicating convective activity at times.
At TAR the temperature pattern was nearly identical to RRS, but as with most 1994 cases
the \\ inds were more \vesterly (- 250" compared to 2250 at RRS). The wind speed was consistently
6-9 m s':. Although the discussion here does not include an analysis of seeding effects, Fig. 48 shows
the period when four valley-based generators were operated, and the ice nucleus measurements
noted at T..t\R. IN were detected above background for most of the operational period. The period
from 1030 to 1130, where an apparent decrease in IN occurred, was actually a period when the
:-JCAR cloud chamber warmed to about - 100, and therefore recorded fewer IN counts. Precipitation
at TAR was steady (panel 4 in Fig. 48) \"ith some peaks near 1 mm h-l. The silver concentrations,
measured from the snow samples collected at T.A.R, were generally below 10 ppt, but the values
greater than about 5-6 ppt are suggestive of silver being incorporated into the snO\'\'fall at TAR. Most
of the higher Ag values occurred benveen 0800 and 1100.
One period of mobile radiometer data was collected at TAR. The values of SL W ranged
from 0.8 mm to less than 0.1 rom. The later period of higher SLW near 1030 occurred as a graupel
shower moved over the site. Microphysical observations at Tl\R indicated crystal riming was
relatively hea\}' throughout the day. Graupel showers were more common after about 1000. Stellar
habits were also observed most of the day, indicating a seeder-feeder process was occurring, but not
efficient enough to entirely remove the SL w.

2. Radar Observations
The K,,-band radar was operated at RRS from about 0730 until 1345. An AFC problem made
the data prior to 0800 unusable. The period of storm which encompassed the mobile radiometer's
observations over the windward slope, the up\..ind highway and the first transect across the plateau

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