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<br />A B S T RAe T <br /> <br />A cloud seeding project was carried out in the vicinity of <br />Lake Tahoe for the purpose of testing whether current seeding <br />technology offers a means of helping to stabilize the level of <br />Pyramid Lake, Nevada, by increasing the flow of the Truckee <br />River; silver iodide aerosol was released from six remotely con- <br />trolled generators located on the upper western slopes of the <br />Sierra Nevada. <br />Over three winter seasons (October 1972 to May 1975), a <br />total of 132 periods of weather (averaging some 35 hours in dura- <br />tion) which were forecast to be suitable for the occurrence of <br />precipitation were designated as "seed" or "no seed" periods on <br />a 50-50 randomized basis. <br />Certain restrictions on the seeding operations were <br />observed in the interest of public safety; for example, seeding <br />was suspended in periods of avalanche or flood danger. The con- <br />centration of silver in falling snow and in surface waters was <br />monitored and found to be such that no deleterious ecological <br />effects could be expected to result from the seeding. <br />An area of 2.725xl09 square meters (1052 square miles) <br />including the northern part of the Tahoe Basin was designated as <br />the "analysis area." Precipitation received during the "seed" <br />and "no seed" periods was measured by means of a combination of <br />23 recording gages and 54 non-recording gages located within or <br />close to the analysis area; 17 sites were equipped with both <br />types of gage. <br />The interpretation of data from the precipitation gages <br />posed significant problems: it was found (a) that heated tip- <br />ping bucket gages, which- comprised the majority of the record- <br />ing gages, yielded substantially smaller estimates of precipi- <br />tation amounts than the non-recording gages, which were <br />considered to be more accurate; and (b) the recording gages <br />malfunctioned on many occasions, especially at the higher <br /> <br />A-l <br />