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<br />been part of several field projects. The most extensive study has been <br />conducted for the Bureau in California by North American Weather Con- <br />sultants in conjunction with a cloud seeding project sponsored by the <br />Naval Weapons Center, China Lake. The conclusion reached ~'as that . <br />extended area effects of cloud seeding may reach as far as 180 nautical <br />miles from the seeding site and can best be explained by changes in <br />cloud dynamics. <br /> <br />Comprehensive field experiments by the Bureau of Reclamation have pro- <br />vided most of the development and field testing of techniques in <br />different areas under different cloud conditions. Winter orographic <br />experiments have been carried on in seven states. Experiments during <br />the 1974-1975 winter season are being conducted in Coloradol and Nevada. <br />Summer cumulus seeding experiments have also been carried out in seven <br />states over the past 13 years. Current plans are for an extensive High <br />Plains experiment on the modification of cumulus clouds over the next <br />5 to 7 years. <br /> <br />Adaptation <br /> <br />Precipitation management technology is sufficiently developed for appli- <br />cation in water-short areas of the nation. The present knowledge about <br />clouds and precipitation, as well as the social, legal, and environmental <br />implications of cloud seeding, is incomplete. But the importance of the <br />water that cloud seeding can provide urges early application of the <br />available capabilities and, from the application, much more can be <br />learned. <br /> <br />Today's technology is reasonably good at recognizing whether a seedable <br />situation exists. The technology is less effective in dete~rmining how <br />much precipitation will fall. It is necessary to predict w'itha rather <br />high degree of confidence how much precipitation will fall from a par- <br />ticular cloud system if it is seeded, and if it is not seeded. Several <br />techniques can be used to make such a determination, but mathematical <br />models are probably the best tools available for the job. <br /> <br />The potential of modeling in precipitation management is sa great that <br />model development will continue to have a high priority. However, models <br />need improvement before they can be used for reliable quantitative precipi- <br />tation predictions. <br /> <br />Day-to-day operational decisions are now based on weather observations <br />and very short-range forecasts - up to about 3 hours. This situation is <br />satisfactory for most precipitation management projects, but it is far <br />from ideal. It would be useful to have an accurate forecast of seasonal <br />precipitation amounts. Not only could the forecast be used. in developing <br /> <br />9 <br />