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e e seeding will be attempted during such warm episodes. However, to be effective, propane must be released directly within cloud, or at least where the air is saturated with respect to ice. Silver iodide, however, has the significant advantage that it can be released well upwind of, and below, the orographic cloud. This can allow much greater time for dispersion so a large volume of cloudy air can be seeded by a single generator. Further, while propane nucleates ice only very near the dispenser, AgI can continue to produce new ice crystals for relatively long periods within cloud. These factors favor AgI seeding whenever cloud is sufficiently cold for the AgI to create ice. It is expected that AgI will continue to be the seeding agent of choice in the Basin, with propane possibly used during warmer storm episodes. Therefore, it is important for AgI seeding tests to choice an experimental area that offers a high frequency of cold SL W cloud near the mountain surface. It is also important that the barrier selected have a long across-the-wind dimension as this will tend to force the air over the barrier. Air follows the path of least resistance and will tend to go around shorter ridges or isolated peaks. An experimental barrier should have a substantial along-the-wind dimension to allow time for ice crystal nucleation by the seeding agent, and subsequent crystal growth and fallout to the surface, before the air reaches the lee subsidence zone. An alternative is to seed from one barrier with the intention of targeting a downwind barrier parallel to the fIrst. Both the Lake Almanor experiment in California, and the Bridger Range Experiment in Montana, used this strategy with apparent success, and current experimental propane seeding in California is using the same approach. To illustrate the requirement for a long across-the-wind dimension, consider that many ice crystals have fall velocities near 30 cm S.l. Such crystals require approximately 2000 s to settle to the surface from the top of a ground-released seeding plume typically reaching 600 m above the surface. Winds in this layer during winter storms usually range between 5-20 m S.l, with 10 m S.l being a typical value. In this example, ice crystals will travel 20 km (12.4 mi) horizontally during their fall with a 10 m S.l average wind speed, and twice that distance with a 20 m S.l wind. Of course, ice crystals formed nearer the mountain surface should take less time (distance) to settle to the ground, ignoring the effects of temperature on ice nucleation and crystal growth rates. Storms with stronger winds (e.g., 15-20 m S.l) tend to produce more forced uplift and more SL W condensate. Such storms should have considerable seeding potential during periods with limited natural ice crystals, provided the crystals can settle to the surface before being carried to the lee of the barrier where sublimation and evaporation take place. Consequently, it is well to have as great an along-the-wind dimension as possible. Mountain barriers that are less than 20 km wide likely will be difficult to. target with seeding-produced crystals during many windier, wetter storms. Many barriers are narrower than 20 km, but it is again noted that seeding from one ridge to target a downwind parallel ridge should be successful. Yet another important factor in a target area is the ability to make accurate snowfall rate measurements at the surface. This key observation is one of the most difficult to make in many mountain areas because of wind-related errors. Precipitation gauges significantly undercatch snowfall with winds of only a few meters per second, and the errors markedly 4