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<br />conducted during all or ponions of the 1975-1979 seeding period in several control <br />counties in Northwest Kansas and Northwest Oklahoma, c) this and subsequent srudies <br />have shown a possible downwind effect on rainfall which would impact the downwind <br />control counties and d) cloud seeding occurs across target counties borders and this may <br />impact rainfall in control counties that are adjacent to target counties. The basic concern <br />is that for the 1975-1979 seeding period, not all of the target counties received cloud <br />seeding operations each year: whereas cloud seeding operations occurred in many control <br />counties, hence the study did not allow a true comparison of rainfall between target areas <br />that received cloud seeding versus control areas that did not receive and were not <br />impacted by cloud seeding. <br /> <br />Third Eyaluation <br /> <br />In 1985, a third evaluation studv entitled" A Statistical-Meteorological Evaluation of <br />- - <br />Two Operational Seeding Projects" was conducted by staff from the Illinois State Water <br />Survey. The Western Kansas Weather Modification Program portion of this srudy <br />focused only on those days for which cloud seeding was conducted for the purpose of <br />rainfall eOhancement and only during the months of May, "July and August from 1975- <br />1979. Days in which cloud seeding operations were being conducted in the target area <br />and in the Harper, Woodward and Ellis County, Oklahoma area were omitted from the <br />analysis. However, this caution was apparently not taken in regard to other cloud <br />seeding operations that were occurring in Northwest Kansas or in Texas County, <br />Oklahoma. In contrast to the 1981 study, a separate control area, based on the existing <br />wind field and storm motions, was designated for each cloud seeding event to minimize <br />contamination of the control area from the seeding material. Each control area was <br />chosen to conform closely to the size and shape of the target area for a specific storm. <br /> <br />The conclusion of the 1985 study was that "although the target area total rainfall for the <br />five years exceeded the control total by nine percent, the difference is too small to <br />provide finn statistical support for seeding-induced increases. "3 This srudy was much <br />more sophisticated than the earlier 1981 study, however there is again some need for <br />caution in interpretation of results due to the fact that many of the control areas selected <br />for individual seeding events may have included or been impacted by other cloud seeding <br />operations. This situation would most likely result in somewhat of an underestimate of <br />the effectiveness of the Northwest Kansas Weather Modification Program. Also, the fact <br />that the results were based on only five years of cloud seeding activity is a liability due <br />to the natural variations in rainfall patterns and the resulting difficulty in finding <br />statistical significance for small changes in rainfall that may be due to the cloud seeding <br />effom. <br /> <br />3 Huff, Floyd A. et ai, "A Statistical-Meteorological Evaluation of Two Operational <br />Seeding Projects," Journal of Climate and Aoolied Meteoroloe:v, Volume 24, No.5, May 1985, <br />p.459. <br /> <br />5 <br />