The area of maximum effect resulting from the Lake Almanor randomized cloud seeding experiment

A randomized cloud seeding experiment was conducted on the Lake Almanor watershed near Mt. Lassen, California, during five winter seasons, 1962-67. The target area extended approximately 20 miles east-west and 15 miles north-south, and ranged in elevation from 4,500 to 6,400 feet, MSL. Silver iodide was released from ground based acetone solution generators which were located between 6,000 and 7,400 feet, MSL. Silver iodide releases were made for 12 hour periods and these periods were subsequently divided into four weather categories, three of which together produced approximately 85% of the total precipitation, no response to the seeding was observed in the target area. In the remaining category, characterized by westerly winds and cold temperatures, the increase peaked at approximately 59% between 5 and 11 miles downwind, and averaged 27% throughout the 21 mile distance. Both results were statistically significant at the 5% level.