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<br />The control area did not include an eastern portion because it was indicated that, due to <br />downwind effects, it would have been necessary to choose counties that are so far to the <br />east of the target counties that they would have had a different climate. <br /> <br />There was no southern portion of the control area because exteIlSive cloud seeding <br />operatioIlS in northwest Oklahoma and some in northwest Texas, preclude the selection <br />of any control area counties that lie close to the southern portion of the target area. <br /> <br />The western portion of the control area was located in Colorado and includes Yuma, Kit <br />Carson, Cheyenne, Kiowa and Prower counties. <br /> <br />Seasonal Precinitation Data <br /> <br />U.S. Department of Commerce Climatological seasonal precipitation data were used for <br />the months of May - August. These four months were active cloud seeding months for <br />each year of the Weather Modification Program during the 1979-1993 time period. <br />Seasonal precipitation data were obtained for each year from 1941-1970, and from 1979- <br />19937. . <br /> <br />Analvsis of Seasonal Precinitation Data <br /> <br />Step 1: <br /> <br />Many counties had more than one precipitation station. Monthly <br />precipitation data from multiple precipitation station counties were <br />averaged for each year, so that each county (control and target) had only <br />one precipitation data value per month per year. <br /> <br />Due to variation in rainfall within a county, the average rainfall reported <br />, <br />from multiple weather statiOIlS within a county provided a more accurate <br />estimate of the actual average rainfall received in the county than would <br />be obtained by using only a single weather station. <br /> <br />Step 2: <br /> <br />An average seasonal precipitation value was calculated each year for the <br />control area and for the target area. <br /> <br />Step 3: <br /> <br />The control area average seasonal precipitation was calculated for the <br />1979-1993 time period by adding the 15 annual control area averages, <br />calculated in step 2, and dividing by 15. <br /> <br />7 Depamnent of Commerce, U.S., National Oceanic and Atmospheric Administration, <br />"Climatological Data," 1941-1970 and 1979-1993. <br /> <br />10 <br />