WMOD00309

• Title: Applications of the Clark Model to Winter Storms Over the Wasatch Plateau
• Prepared For: Utah Department of Natural Resources Division of Water Resources
• Prepared By: James A. Heimbach, Jr.
• Date: 7/1/1993
• State: UT
• Weather Modification - Doc Type: Report

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f. Simulated Ag! Release from Low Area West of San Pitch Mountains, 2 March 1991.
A release site was inadvertently modeled for the 2nd which turned out to be an instructive simulation. Its
latitude, longitude and elevation are 390 33.5', -1110 48.0' and 1800 m. Its position is shown in Fig. 20. A
simulated Skyfire generator was placed at this point and 30 gms hr-I was released for 3 hr following an initial 1 hr
integration. The surface plot shows the AgI being channeled through low lying terrain and moving into the Sanpete
Valley. There was some weak vertical motion derived by the model associated with the upwind slopes and this
helped move the plume over some higher terrain as shown in Fig. 21 which is valid for the same time at 2.2 km.
The next higher analysis, 2.9 km, had no contours of AgI for this time; however, previous times did (not shown),
demonstrating the temporal variability of vertical motion found by the model. Fig. 22, a vertical cross section, shows
the plume moving over higher terrain, then downward again into the Sanpete Valley. The contours are limited to
several hundred meters above the topography.
This release point provided a better starting point for a seeding agent than the previously discussed San Pitch
point. This is because the previously discussed point was located in an area of negative w, whereas the release point
of this section had some positive w to immediately help with vertical transport. After 3 hr, no contours reached the
Wasatch Plateau, however, the model probably diluted the plume too much to have the rninimum contour be applied
at this range.
g. Simulated Release from Windward Slope of San Pitch, 2 March 1991
The previously described San Pitch simulations illustrate the sensitivity of transport and diffusion to the
vertical velocity field. In this section a release site is selected solely by the vertical velocity. Figure 8 indicates an
organized positive w zone on the west slopes of the San Pitch mountains for 2 March. A simulated Skyfire generator
was placed in the middle of this area, which turned out to have an elevation of 2.5 km, the approximate elevation
of the HAS. Its latitude and longitude are 39037.0' and -1110 45.0'. Topography maps show this area to have
ridges extending downward from the crest. This is similar to the Bridger Range Experiment's seeding sites which
were near 2.2 lan, two-thirds of the way up the windward side of the barrier (Super and Heimbach, 1983). This
experiment demonstrated consistent transport of seeding material over the 2.6 km crest line to the target area which
was a secondary ridge 10 to 20 km to the east. Super and Boe (1988) give further confinnation of the viability of
windward slopes for surface seeding releases in their description of two cases in the Grand Mesa of Colorado. Silver
iodide was released 0.5 km below the top of the 3.2 to 3.3 km mesa and detected by an aircraft at 4.6 km.
The Skyfire generator was used in this simulation and the AgI release was started after 1 hr initialhintegration of the model. Figure 23 is a plot of surface concentrations of AgI valid 1 hr after the release started.
This shows a consistent transport over the crest which, from Fig. 24, valid for the same time, shows mixing to 2.9
km. The vertical WoE cross section, Fig. 25, gives a less optimistic picture, showing the plume to be moving down
the lee slope; however, it is rnixed through several hundred meters. Figure 25 is for the 85 km point and does not
go through the areas having transport to 2.9 km.