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<br />ooa146 <br /> <br />the Uinta, and the Upper Green are in the Upper Colorado River Basin and <br />naturally produce 75 percent of the total Basin's water supply. These areas <br />include about 13,000 square miles, or 12 percent of the total Upper Basin <br />area. The Mogollon Rim, covering about 9,600 square miles, is in the Lower <br />Colorado River Basin. Most of all six areas are public lands. <br /> <br />CREST consists of five major components: the demonstration program; trans- <br />ferability studies; extra-area effects studies; environmental, social, and <br />legal considerations; and comprehensive evaluation and reporting. <br /> <br />The main objective of the demonstration program is to produce additional <br />water in the Colorado River Basin and thereby confirm and quantify the <br />feasibility of using weather modification for increasing snowpack and sub- <br />sequent runoff. Based on scientific and logistical considerations, the <br />preferred sites for the demonstration tests are the White River Plateau and <br />the San Juan Mountains, both in Colorado. These two sites present a diver- <br />sity of terrain and meteorological characteristics that are representative of <br />those occurring over the ent ire Bas in. <br /> <br />The general hypothesis underlying CREST has evolved from a number of weather <br />modification projects, including several in the Colorado River Basin. The <br />hypothesis can be summarized as follows: <br /> <br />The flow of moist air over mountain barriers produces liquid water drop- <br />lets at rates determined by the temperature, humidity, and upward motion <br />of the air; these tiny droplets tend to evaporate rapidly in the descend- <br />ing air in the lee of the mountain barriers. <br /> <br />The droplets tend to remain in the liquid state at temperatures lower than <br />o .C due to the scarcity of ice-forming nuclei in the free atmosphere; <br />they are referred to as supercooled droplets, and the clouds they form are <br />called supercooled clouds. <br /> <br />Ice particles present in the supercooled cloud grow at the expense of the <br />supercooled droplets, and the largest particles reach the surface as <br />snow. <br /> <br />The natural ice-particle concentration is sometimes less than required for <br />maximum precipitation fallout; increasing the ice-particle concentration, <br />by using seeding material that causes more ice crystals to form, can <br />convert more of the supercooled droplets to snow and decrease the amount <br />of moisture lost to the lee of the barrier. <br /> <br />Clouds are considered seedable in this "static" seeding hypothesis if <br />(1) the collision-coalescence process between cloud drops is inefficient, <br />(2) the rate of formation of supercooled droplets is comparable to or <br />exceeds the rate of depletion of supercooled water, and (3) there is <br />sufficient time for seeding-produced precipitation particles to grow big <br />enough to fall to the ground. <br /> <br />Seedable clouds occur in two general types of storms that affect the Colorado <br />River Basin: (1) large synoptic storms that produce wide spread precipi- <br />tation over large areas that include both mountains and valleys, and <br /> <br />2 <br /> <br />-. <br />