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Bulletin American Meteorological Society 491 FIG. 2. Areas containing mountain crests suitable for winter-orographic precipitation management applications. more than isolated shower clouds do. Promotion of mergers in borderline cases may prove effective for rain augmentation. However, since such mergers and trans- formations occur naturally when the potential for severe weather is high, the likelihood that seeding for pre- cipitation increase would take place in the face of the risk of severe weather and that it would increase the frequency of damaging storms appears slight. There may be an exception when hailstorms are seeded for the joint purp.ose of rain increase and hail suppression, in which case, however, the hail suppression motive would domi- nate. There is a broad consensus in the scientific com- munity that the potential of the methods currently under development does not exceed the range of 10- 30% increase in the areawide, season-long precipitation. It is appropriate to take the liberal end of this range in assessing the effect that stimulated precipitation might have on other components of the environment. 2) WINTER-OROGRAPHIC CLOUDS There is somewhat better agreement among experts as to increases that may be expected from winter- orographic cloud seeding, and it is generally regarded as closer to the point where the potential of a mature technology can be predicted. It has become evident that site factors loom large. For practical reasons, sites with potentials much <10% increase from seeding are un- likely to become the scene of operations. For the most favored localities, an increase of 30% could be regarded as a generous but not unreasonable. expectation from a mature technology intensively applied. . In the experimental situations that have received the most intensive study, storms thought most suitable for stimulation are those with moderate cloud depth and wind strength. These, when seeded, deposit additional snowflakes near the mountain crests. Storms with very deep cloud systems and strong winds apparently already supply enough, perhaps too many, ice nuclei for pre- cipitation, and any added snow crystals formed by seed- ing blow beyond the mountains and reevaporate. In some cases, however, no reliable relationship between the severity of a storm and its susceptibility to seeding has been found. Considering the constraints likely to be imposed on the seeding of severe storms, it is likely that the frequency of moderate snowfaps will be increased much more than the frequency of severe ones. Tenta- tively, the same conclusion may be stated with respect to storm duration. 3) EFFECT ON PRECIPITATION IN NEARBY AREAS It is surprising how many people, including those who commented on the_ draft version of the Skywater en- vironmental statement, appear to assume as inevitable that augmentation of precipitation in one place must cause its diminution somewhere else. Most often cited in support of this plausible but fallacious assumption is the notion that the extraction of moisture by augmented precipitation dries out the atmosphere and, thus, leaves it less capable of producing subsequent precipitation. The fallacy lies in failure to appreciate 1) the role of natural atmospheric disturbances in causing the con- vergence and ascent of moist air as the dominant mechanism that makes moisture available for cloud formation and 2) the potential of cloud seeding both for increasing the dynamic energy of such disturbances and for increasing the efficiency with which the storm clouds are converted to precipitation (storm clouds that would naturally "blowout" a greater proportion of their moisture to the stratosphere). Model studies of convec- tive rain clouds are not far enough advanced to predict the outcomes with high confidence, but at least they