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<br />separately and the results indicated a 9-p~rcent p~e~ipitation <br />incre~se.for.Climax.I (251 cases) and a .39...percent increase for <br />Climax 1I<(29 cases) . Results from this experiment established <br />the relationship of cloud-top temperature with both positive and <br />negative seeding effects. <br /> <br />Subsequent analyses conducted by Colorado State University revealed <br />some evidence that the distribution of meteorological events between <br />seeded and nonseeded events was not random. A possible bias was <br />found in that seeded days tended to be naturally wetter than <br />nonseeded days. However, further analyses have showntltat statistical <br />tests utilizing control station precipitation substantiate earlier <br />results. <br /> <br />Wolf Creek Pass Experiment <br /> <br />The Wolf Creek Pass experiment was essentially an operational <br />snowfall augmentation program conducted by Colorado State University <br />for the State of Colorado from 1964 to 1970. The target area was <br />the Wolf Creek ~ass region of the San Juan Mountains in south- <br />western Colorado. The basic design consisted of a yearly <br />randomization with 24...hQur experimental units which were selected. <br />on the basis of precipitation falling at one or more of the <br />sampling stations on Wolf Creek Pass or at a control station. <br />Seeding was conducted using ground-based silver-iodide/acetone <br />generators placed at varying distances from the target area. <br /> <br />The evaluation compared precipitation measurements from the summit <br />of Wolf Creek Pass with seven National Weather Service control <br />stations. The statistical methods were identical to those used <br />for the Climax experiments. The results indicated an increase of <br />52pe1;c:~n1;.w:i1;.l:144l c~ses. Rangno 1]./ has recently examined these <br />results and believes the meteorological conditions that occurred <br />during the nonseeded seasons brought unusually light precipitation <br />to the entire Four Corners area of the western United States. This <br />apparent bias could have resulted in a high ratio of seeded to <br />nonseeded precipitation in the target area. Rangno also believes <br />that this pattern exhibited itself in other watersheds with <br />similar exposures in the area. A reanalysis of this experiment, <br />incorporating control station precipitation, is planned. <br /> <br />Colorado River Basin Pilot Project <br /> <br />The Colorado River Basin Pilot Project was a 5-year Skywater program <br />(1970-75) conducted by the Water and Power Resources Service to test <br />the physical concepts for weather modification and their opera- <br />tional potential. The project target area was the San Juan <br /> <br />IV-2 <br />