WMOD00528

• Title: The Feasibility of Enhancing Streamflow in the Silver Iodide in the Sevier River Basin of Utah bt Seeding Winter Mountain Clouds
• Date: 12/1/1991
• Weather Modification - Doc Type: Report

in section 3.3.1, to approximate the frequency of potentially seedable stonns over a much longer period
of record than possible with microwave radiometer data.

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TUSHAR MOUNTAINS
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R = 0.75
N = 27

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100. 200 300 400

Total SLW Flux (Mg/m)

Figure 3-1. - Storm total SLW flux vs. total precipitation (water equivalent)
based on 1985, 1987, and 1989 data from Tushar Mountains.

The 1985 field program in the Tushars was 2.0 months long, while the 1987 and 1989 programs were
1.5 months in duration. The average number of stonns per month were 9.0 in 1985, 7.3 in 1987 and 3.3
in 1989. Huggins (1990a) classified the precipitation during the 1985 and 1987 research periods as dry
and nonnal, respectively. A similar classification was not given for the 1989 season although Huggins
(1990b) notes stonns were infrequent but wann. Similar data from northern Arizona indicated 6.5 stonns
per month in early 1987 (Super and Boe, 1988a), a period with slightly above nonnal precipitation. This
admittedly limited data set suggests that perhaps six to seven stonns per month might be expected to pass
over the Sevier River Basin during a typical winter month.

The previous discussion concerning total SL W flux per stonn episode may give the impn::ssion that the
only periods worth seeding have large amounts of vertically integrated SLW, In fact, Super and Boe
(1988a) examined 2 months of hourly (not stonn total) microwave radiometer data from nmthem Arizona
to show that 44 percent of the total flux for the season was due to the 81 percent of all hours with mean
cloud liquid water amounts of only 0.15 mm or less. Their study also shows that the 6 percent of all
hours with liquid amounts in excess of 0.35 mm yielded almost 30 percent of the total flux. This suggests
that seeding should be conducted whenever SL W is present, whether amounts are abundant or limited.

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