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<br />10 <br /> <br /> <br /> 5 <br />,....., <br />d <br />c- <br />o. <br />oc:) <br />~ 0 <br />0... <br />'()' <br />'-" <br />~ <br />::l -5 <br />..... <br />e <br />Q) <br />0. <br />8 <br />~ <br /> -10 <br /> <br />-15 <br /> <br />Oct <br /> <br />Nov <br /> <br />Dee <br /> <br />Jan Feb <br />Month <br /> <br />Mar <br /> <br />Apr <br /> <br />May <br /> <br />~ waterXI0 ~ snow ~ Tavg <br /> <br />Figure 3-12. - Average daily precipitation (X10), snow depth, and temperature at the <br />Blowhard Mountain radar site for the months October through May. <br /> <br />The high frequency of cases near -6 oC has interesting implications. If a type of AgI were developed that <br />produced significant concentrations of ice nuclei at, say, -6 oC, many more stonns would be seedable <br />from the ground. The exact temperature at which various types of AgI can produce adequate ice nuclei <br />concentrations is still open to question. Most estimates, including those in this report, are based on cloud <br />simulation chamber reSults. However, conditions in actual mountain clouds may differ, for example, cloud <br />chamber simulations are usually done with higher liquid water contents and droplet concentrations than <br />typical of winter orographic clouds. Deshler and Reynolds (1990) indicated that a particular type of AgI <br />may have exceeded laboratory nucleation activity in clouds over the Sierra Nevada. <br /> <br />The option of propane seeding (Reynolds, 1989; Reynolds, 1991) for the wanner stonns deserves further <br />investigation. It is probable that a significant fraction of Utah winter stonns cannot be effectively treated <br />with ground releases of AgI because the particles will not reach cold enough levels for significant <br />nucleation. But propane can create ice particles at temperatures as wann as 0 oC so many more stonns <br />could be effectively treated with it. A disadvantage of propane seeding is that it must be released in cloud <br />or at least ice saturation conditions for the chilling of the air to produce ice embryos. This requires <br />operation of propane dispensers well up the mountainsides. <br /> <br />3.3.2 Streamflow data. . The main stream draining the Cedar Breaks area is Mammoth Creek. <br />Monthly and water year streamflow data were obtained for this creek for a period of record similar to the <br />Blowhard Mountain observations. Figure 3-14 shows the variations in water year runoff for the 1965-85 <br />period for Mammoth Creek at Hatch. The fairly dry 1970's are contrasted to the abnonnally wet 1980's. <br />Annual runoff values ranged widely, from about 20 to 230 percent of the period's average value of <br />38,620 acre-ft. <br /> <br />Figure 3-15 compares the water year percent of nonnal runoff values with winter season percent of nonnal <br />snowfall at Blowhard Mountain. A linear correlation coefficient of 0.87 resulted, indicating the snowfall <br /> <br />28 <br />