Winter_Cloud_Seeding_Program_in_Utah_Text.doc - A WINTER...

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A WINTER CLOUD SEEDING PROGRAM IN UTAH Don A. Griffith, John R. Thompson, and Dan A. Risch North American Weather Consultants Salt Lake City, Utah ABSTRACT 1
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A winter orographic cloud seeding program has been conducted over the higher elevation areas of central and southern Utah for 13 winter seasons. The primary seeding mode has been ground-based, manually operated "silver iodide generators" located in valley and foothill locations upwind of the intended higher elevation target areas. The goal of this program is to augment naturally occurring snowfall in these higher elevation areas. Resulting augmented spring and summer streamflow is utilized for irrigation. A target/control evaluation of this program indicates approximately an average 11 percent increase in precipitation in the target area over that predicted from the control area precipitation. A similar evaluation of precipitation falling in a lower elevation region downwind of the intended target area indicates an average excess of approximately 15 percent. 1.0 INTRODUCTION A cloud seeding program has been conducted in portions of Utah every winter season since the 1973-74 season, except for 1983-84. The goal of this program has been to augment naturally occurring snowpack in the higher elevation regions. The augmented snowpack is intended to augment surface streamflow used for irrigation. This program has been administered by a non-profit organization known as the Utah Water Resources Development Corporation. This program was initiated at the county level for the first two years that cloud seeding was conducted. The State of Utah, through the Division of Water Resources, has provided financial cost sharing assistance to the participating counties since the 1975-76 winter season. County participation in the cloud seeding program has been determined each fall through either the County Board of Supervisors or County Water Conservancy Districts. North American Weather Consultants (NAWC) has been the contractor selected to conduct this program by the Utah Water Resources Development Corporation each winter of operation. 2.0 BACKGROUND 2
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The Utah winter cloud seeding program originated in the central and southern portions of the State, partially in response to drought conditions that affected the State in the early 1970's. Several organizational meetings were conducted with county officials in the summer and fall of 1973. Methods of financing an operational cloud seeding program were discussed and a formula established which allocated the proposed contract costs to the participating counties on the basis of county assessed valuation. Seeding first began in January of 1974. The next seeding program started in December the following winter season of 1974. The normal period of operation after these first two years has been November 15 through April 15. This period was selected to concentrate on the primary period of snowpack accumulation.
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