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<br />175 <br /> <br />polation of radiosonde-reported humidities downwind and up- <br />ward was also frequently useful on a shorter time-scale. <br /> <br />No satellite imagery was available, although discussions <br /> <br /> <br />of such images that came over the teletype in the forecast <br /> <br /> <br />office at the airport were helpful. <br /> <br /> <br />The window period in which there was high-level moisture <br /> <br /> <br />out little low-level moisture was variable, but seemed to <br /> <br />average maybe 6 to 12 hours over Colorado Springs. These <br />were wintertime conditions, of course. Persistent totally <br /> <br />dry periods were noted, lasting many days, however, as were <br /> <br />persistent periods of 10w-level cloudiness. In so-cal1ed <br />"upslope" conditions, where air flows from the east against <br />the Rockies, low clouds developed before high ones. <br />After two seasons' experience, it generally was possible, <br />using a variety of indicators as discussed above, to fore- <br />cast 12 to 24 hours in advance whether the general possibility <br />of clear-air seeding would exist in one of the two opera- <br />tional areas (New Mexico or El Paso County). The second <br /> <br />season proved to be very successful for forecasting. The <br /> <br /> <br />three cases where no cloud was produced were marked by equip- <br /> <br /> <br />ment problems or were flights made when seeding was only a <br /> <br /> <br />secondary objective. <br /> <br />Cloud Properties <br /> <br /> <br />The third aim of the program, to study the microphysical <br /> <br /> <br />properties of artificially produced clouds, was not achieved <br /> <br /> <br />to any great degree. The particle counter system suffered <br />