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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of the edge of the plateau, and attributed this to removal by precipitation, or a negative slope of the
mountain wave which could produce downward moving air up\'\ind of the physical crest of the
plateau.
The first comparison period was 0400 to 0800 when the mobile radiometer was stationary
at HQ between O-lOO and 0650, and then was driven from HQ to RRS be1\veen 0650 and 0800. The
DR! and CSBR SL W depth plots for this period are shown in Fig. 52a. While the two radiometers
were stationary their temporal trends were quite similar between 0510 and 0630, with the onset of
SL W being at the same time and a gradual increase occurring at about the same rate. After 0630 the
SL \\" oyer RRS continued to increase through 0720, while the depth over HQ leveled off: the
greatest difference of 0.60 mm occurred at about 0700 at a time when cloud base had lowered to
RRS or below. On its ascent to RRS the mobile radiometer detected a SL W maximum at 0730 near
the upv\-ind edge of the plateau. From 0745 to 0800 the mobile radiometer was near RRS and
measured depths nearly identical to those from the USBR radiometer. This agreement verified the
calibrations of the 1\vo instruments, and indicated that a comparison of the absolute measurements
of the two radiometers was valid.
From 0815 to 0900 the mobile radiometer was driven across the plateau to TAR (Fig. 52b)
and measured SL \V depths from 0.6-0.9 mm. Over the same period the radiometer at RRS measured
depths consistently above 0.9 mm. Figure 52b also shows a comparison of the two instruments
during a two hour period when the mobile unit was stationary at TAR (0900-1100). The temporal
patterns of the 1\VO data sets were nearly identical during this 2-h period, vv;th the dovYTIwind depths
being 0.3-0.6 mm less than the upwind depths. The two sites were at similar altitudes (2982 vs. 2902
m). and were positioned where local terrain provided uplift in southwesterly flow.
To test whether precipitation between RRS and Ti\R could account for the SLW depth
difference a simple calculation was made. To account for travel time betvveen RRS and TAR, a 15-
min lag v,;as assumed and the average SL\V depth at RRS from 0845-1045 was compared to the
average SLW depth at T.-'\R from 0900-1100. The RRS average was 0.8206 mm and the TAR
average was 0.3668 mm. Using the wind speed at.RRS as an estimate of the \\;nd in the SLW layer,
the difference in SL \V depth was convened to a flux. This was done by normalizing the radiometer
depths to 1 m2, so that 1 mm convened to 1000 g m-2. Upon multiplying by the \\'ind speed, the

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