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e e increase with wind speed. This is because some of the air flows upward over the gauge orifice, reducing the "catch" of slowly falling snowflakes. Various types of windshields have been used to reduce gauge undercatch, but none satisfactorily solves the problem in the windy areas common in mountain regions. The most practical solution appears to be to locate gauges in small protected clearings where conifer forest is available. Of course, many mountains have significant areas above timberline where this is not possible. Large open areas are common even below timberline. Special structures have been constructed to shield gauges in windy places (e.g., the Wyoming gauge), but reported results have been mixed. There is no proven satisfactory method to measure surface snowfall in windy, open areas. It is, therefore, prudent to consider the availability of conifer forest cover when selecting an experimental area (deciduous trees which shed their leaves before winter are usually unsuitable for shielding gauges). We will summarize the characteristics of an "ideal" mountain barrier for weather modification experimentation. Most winter storms in the West are characterized by ridgetop-Ievel airflow between southwest to northwest. Thus, the ideal barrier would have a long north-south extent to force the prevailing airflow over rather than around the barrier. The mountain barrier would have a wide top with limited local relief, or possibly have two parallel ridges bisected by a north-south valley. In the latter case at least the downwind target ridge would be fairly wide with limited relief on top. The barrier would be high enough to have permanent snowcover from sometime in November until late in the spring, thereby providing a long experimental season. It.is essential that the highest terrain exceed approximately 2740 m (9000 ft) in order to provide a SLW zone near the surface cold enough for effective AgI seeding for several months each winter. Moreover, most snow accumulation is above the 9000 ft contour as discussed by Weisbecker (1972). This 9000 ft requirement excludes the Mogollon Rim of Arizona which has an intermittent winter snowpack and rather warm temperatures at levels likely to be affected by ground-based silver iodide generators. Super et ale (1989) pointed out that aircraft seeding would likely be required for most winter storms over the Mogollon Rim. The ideal barrier would have a high frequency of winter storm passages. That need is significantly better satisfied in the Upper Colorado Basin than in the Lower Basin. Even within the Upper Basin, a marked south-to-north increase in storm frequency is known to exist. All else being equal, the "ideal" experimental area would be as far north as possible to provide the highest storm frequency and also the colder storms more likely to be seedable with ground-released agents. However, from the standpoint of transferability of results, an experimental area near the higher terrain portions of the Basin would be preferable. The ideal experimental area would not be near a wilderness area, including upwind and downwind of the target. Release of seeding agents and various measurements of cloud characteristics need to be made upwind of the target. Measurements of at least precipitation should be made for some distance downwind of the intended target to investigate the distance over which seeding has a detectable effect (Le., "downwind effects"). 5