An industrial operation to produce precipitation

Cloud seeding (weather modification) experiments were carried out at Bishop Creek, California, during the winters of 1947-49. It was observed that clouds forming over the watershed were blown east and dispersed without precipitating. These clouds are usually deficient in nuclei and had temperatures between -10deg and -39deg C. Dry ice, distributed by airplane at the rate of 4 to 5 pounds per mile, was found to be superior to silver iodide. Precipitation occurred from 5 to 15 minutes after seeding. Over-seeding caused the dispersal of clouds. It was estimated that seeding operations increased the water yield by 14% in 1947-48 and 12% in 1948-49. The cost was approximately $200 per hour of seeding flight time, with flights ranging from 45 minutes to 1.5 hours. Approximately 50 flights were made in 1948-49.