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<br />NOAA WEATHER SERVICE DATA <br />PROGRAM CENTRAL HEADQUARTERS <br />OTHER OPERATING DISTRICT CONTROL CENTERS <br />Fig.6. Proposed WOSA Information and control system <br />ration from the land surface or vegetation. Much of the moisture <br />in the winter snowpac]s: is lost through evaporation from the <br />surface of the snowpack. If the snow is deeper but covers the <br />same area, ~vaporation will not increase significantly. A heavy <br />snowpack may stay on the ground for a few weeks longer in the <br />springtime when the evaporation losses are high, but overall, a <br />heavy snowpack loses a smaller proportion by evaporation than <br />a light snowpack. <br />25 <br /> <br />--... <br />.......-----........ <br />y <br />---. ,-..., ---. <br /> <br />INTENSITY <br /> <br />~~....... <br /> <br /> <br />'-e! WEATHER <br />~ SATELLITE ,.r ~ <br />'""- CLOUD COVER <br />~~ COVER <br /> <br /> <br />~ r---~ ~ <br /> <br />RADIOfSONDE PRE~~~:~ION- ~ <br />WIND SPEED "" <br />AND DIRECTION / <br />IV~ \J--/~ . ~~.A <br />: . TEMPERATURE <br />/;: J ~SSURE <br />(/ <br />filLVER 10011 <br />GENERATO <br /> <br />SNOWPACK, CLOUD-SEEDING, AND THE COLORADO RIVER <br /> <br />conditions that would be suitable for cloud-seeding would not <br />occur at the same time throughout the region. In addition, the <br />seeding conditions that would produce the best results would <br />differ from range to range. An operational WOSA program in <br />an area as large as the Upper Colorado River Basin cannot be <br />one massive basin-wide operation; instead, it must combine and <br />coordinate a great many separate operations. <br />The area that is suitable for cloud-seeding can be divided <br />into ten districts, each small enough to have fairly uniform <br />weather as a storm passes through the Upper Basin. Silver iodide <br />smoke generators will be located at fixed positions upwind of <br />each target area. The number of generators will depend upon <br />the size of the target area, and the locations will be chosen to <br />make the generators effective under the weather conditions that <br />bring most of the seedable storms to the target area. The gen- <br />erators can be turned on or off and can be operated at either of <br />two pre-set burning rates. Each district will have several gen- <br />erators to control, and the trick is to know which ones to operate <br />at which burning rate to achieve the best possible cloud-seeding <br />results. Because weather conditions can change so rapidly, it is <br />necessary to re-evaluate the situation at least every hour. <br />. The generator operating decisions are made on the basis <br />of cloud top and mountain top weather conditions-wind speed <br />and direction, temperature, barometric pressure, and humidity <br />-and the concentration of ice nuclei. If no more snow aug- <br />mentation is wanted in a target area, the generators can be <br />switched off. This requires an elaborate iD.formation and control <br />system such as that sketched in Figure 6. <br /> <br /> <br />r.: <br /> <br />the Mountains to the River <br /> <br />In an average year, around 93 million acre-feet of water falls as <br />rain or snow in the Upper Colorado River Basin. (An acre-foot <br />is enough to cover an acre with one foot of water.) From <br />measurements of the water that ends up as stream flow, it is <br />estimated that about 78 million acre-feet must be lost by evapo- <br /> <br />24 <br /> <br />\ <br /> <br />From <br /> <br />