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<br />e <br /> <br />e <br /> <br />downwind effects expressed by some people living near the Unitas. They suspect that <br />operational seeding upwind of them is effective and is depriving them of some of their <br />natural snowfall. However, local officials believe that an experiment to evaluate seeding <br />effects would be welcomed even in the Unitas. <br /> <br />9. Shadowing by upwind mountains <br /> <br />Shadowing by upwind terrain, as high or higher than the proposed target area, can <br />seriously hinder experimentation. Ice crystal formation over upwind mountains can <br />substantially affect snowfall forming processes over the next downwind barrier. For <br />example, Marwitz and Stewart (1978) cautioned that with westerly winds, the snowfall on <br />the Unita Range of Utah was strongly influenced by the carryover of ice crystals initiated <br />over the upwind Wasatch Range. Upwind mountains can also markedly influence <br />downwind flow patterns, both horizontally and vertically (e.g., by setting off gravity <br />waves). Thus, the presence of upwind mountains can "contaminate" or complicate seeding <br />experiments with unwanted effects. Conversely, the presence of an upwind barrier that <br />does not overshadow the experimental area may offer significant advantages in siting <br />seeding generators. Shadowing effects rated as "considerable" means the influence of <br />upwind barriers was considered likely to hamper experimentation. <br /> <br />10. Proximity to a town <br /> <br />The proximity to an adequate town was rated jointly by the travel time from the <br />experimental area to the town, and the likelihood that the town had desired housing, <br />supplies and services. The latter estimate was based on town size unless personal <br />experience was available. <br /> <br />11. Major axis <br /> <br />Most barriers in the ColOl:ado River Drainage have their major axis generally north-south, <br />across the prevailing westerly flow during storms. Some mountains, such as the Unitas <br />in Utah and the Grand Mesa in Colorado have an east-west major axis. Since east-west <br />oriented barriers are atypical they might be less desirable for experimentation. Moreover, <br />as noted earlier for the Grand Mesa, low-level winds can be from "either north or south <br />depending upon the stage of a storm sequence. That c~ seriously complicate placement <br />of experimental equipment. Seeding generators are needed both north and south of east- <br />west barriers. Moreover, observing equipment may need to be duplicated at different <br />locations; for example, on two different "downwind" edges of the barrier. All else being <br />equal, a north-south barrier is to be preferred. However, it should be noted that when <br />individual mountain regions are studied at the relatively small scale of an experimental <br />area, many barriers are "atypical" and some have no predominant axis. <br /> <br />12. Wilderness area impacts <br /> <br />Possible impacts by wilderness areas is another subjective evaluation. It could be a <br />problem if it impacted on the" data needed for an experiment. For example, a wilderness <br />areas downwind of an experimental area would hinder study of possible "downwind <br />effects" on precipitation since gauges could not be maintained. Wilderness area locations <br /> <br />10 <br />