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<br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br /> <br />expanded to allow a greater understanding of the long-term, extra-area effects of cloud seeding. <br />Though environmental assessments have to date found that commonly used seeding chemicals are not <br />toxic to the environment, additional environmental monitoring should accompany research and <br />operations where warranted. <br /> <br />HAIL <br /> <br />Hailstorms annually produce major property losses in many countries; these disasters are <br />increasing in frequency, with property losses rapidly overtaking the previously dominant crop losses, <br />though the latter have not diminished. For example, annual u.s. crop losses due to hail average $2.3 <br />billion, with 5 to 6 percent of the High Plains crop value lost each year, and an additional 1 to 2 <br />percent of the crop value lost to hail in the Southeast and Midwest. In 1998, the Institute for <br />Business and Home Safety (IBHS) reported that in the U.S. for the period from 1994 through mid- <br />1997, $13.21 billion in catastrophic losses resulted from hailstorms, second only to the $14.73 billion <br />losses due to the Northridge, California earthquake. Presently, there are approximately 17 countries <br />where serious operational hail suppression programs are in progress. <br /> <br />Recent peer-reviewed evaluations of the operational North Dakota hail suppression program <br />show a 45% reduction in crop-hail damage and an additional $24.7 million of annual economic benefit <br />in the target counties. A 27% reduction has been reported for a similar Kansas program. While <br />recent thunderstorm research has made progress in verifying the seeding agent transport and <br />dispersion, and ice nucleation within developing flanking line turrets, the hail embryo source regions <br />have not been identified. Storm-scale models can be used to simulate and study hailstorms and the <br />effects of cloud seeding upon them. Previous modeling efforts have successfully simulated the <br />evolution ofthunderstorms of various complexities, with the attendant fall ofhail. Some simulations <br />have included the effects of seeding upon the storms. Further modeling will result in greater <br />understanding and better forecasting of hail development, and improved procedures for the <br />suppression of hail. <br /> <br />The use of numerical models for short-term hail prediction should be expanded, tested against <br />observations, and developed into a comprehensive hail warning system. Before such a system could <br />be used operationally, more confidence in our numerical capability to predict hail damage (based on <br />hail size and wind gusts) is needed. Continued testing of operational hail suppression techniques is <br />needed, including comparison of seeded and non-seeded storm characteristics against numerical <br />simulations. Direct measurements in the storms themselves are required to validate the numerical <br />simulations of seeding effects and to develop confidence in the conceptual models for hail <br />suppreSSIon. <br /> <br />A 1995 international meeting of experts on hail suppression, sponsored by the World <br />Meteorological Organization, strongly recommended continued research such as that described <br />immediately above. <br />