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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layer. The sounding v"inds were consistent with the observations from I-lA.S, RRS, TAR and the
Doppler sounder. The 8e profile indicates slight convective instability existed in the moist layer.

2. Radar Summary
The K,,-band radar at RRS collected data from 1022 MST through about 1710 MST: about
10 min before the start of seeding to about 1.5 h after seeding ended. The echo patterns at
approximately hourly intervals throughout the seeding period are shown in Fig. 38.
At 1103 (Fig. 38a), about 20 min after the start of seeding, there was a very weak echo return
over the plateau with a band of higher reflectivity over the windward slope of the plateau in the
vicinity of the seeding generators. Over the next three hours radar echo generally intensified over
the plateau, so that by 1410 (Fig. 38d) a relatively large region of Level 45 echo surrounded the
radar. The highest returns remained up\vind of RRS, but a narrow band of enhanced echo also
appeared near the dO\\TIwind edge of the plateau after 1300 (Fig. 38 c,d). The enhancement of echo
with time was fairly \videspread, and included areas upwind of the seeding generators. This suggests
that the enhancement was not a seeding effect.
After 1500 the echo intensity over the plateau began to diminish, and by 1610 (Fig. 38f) the
Level 40 and greater echo was confined to a region in the southwest quadrant. The increase in liquid
\vater, noted in Fig. 35 after about 1430, appears to be associated with the decrease in radar return
over the highway to the north of the radar. The north-south band of enhanced reflectivity to the
northeast of the radar remained in place even as the echo intensities decreased. As vvith the earlier
periods, there was no obvious seeding enhancement in the later PPI's.
The temporal trend in radar reflectivity is more easily seen in time-height plots of maximum
echo observed over the Flat Canyon precipitation gage (Fig. 39) and the target site (TAR) in Fig. 40.
O"'er Flat Canyon near the center of the plateau echo intensity increased markedly to 10 dBZi at
1200, and continued at similar levels through 1600. The echo heights also increased about 200 m
between 1100 and 1300. The echo maxima observed over TAR were more sporadic and generally
smaller in magnitude than over Flat Canyon. W~th the radar sampling at greater heights above the
surface o"'er TAR, there was also evidence of ice up to 4 km MSL. The maxima observed near the
surface at 1500 and 1600 appear to have originated in a band of higher (colder) cloud.

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