An analysis of a series of cloud seeding projects conducted in three different Pacific-slope watershed areas, each during several seasons, is presented. Seven separate project-seasons are involved in each of which identical seeding procedures were used. Silver iodide smoke generators were operated at ground level for a total of well over 10,000 generator-hours during these operations.

Snowpack and other official precipitation records are examined and target-to-control-area comparisons made in order to bring out the effects of the seeding and apply statistical tests thereto.

It is concluded that this evaluation procedure, as applied to the available data, is capable of discerning the effectiveness of cloud seeding in increasing precipitation over a period of several seasons, but is not capable of bringing into focus the many details of interest to the cloud seeder.

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