Precipitation enhancement, commonly called “cloud seeding” or “weather modification” is a scientific method to artificially stimulate clouds to produce more rainfall and snowfall than would be produced naturally. The primary mechanism is to inject substances, such as silver iodide or ice crystals (cloud seeding agents), into the clouds, enabling snowflakes and raindrops to form more easily. Various cloud seeding programs have been operational since the late 1950s. The majority of programs continue for a number of years during winter months and as conditions warrant. The following is a summary on previous cloud seeding programs in California.
It probably made a difference this year. It can’t change the frequency of storms as those come from the Pacific Ocean. But when it does rain it can make it rain about 10-15% heavier.
Cloud seeding is particularly important for San Francisco, who only get rights peak runoff amounts due to the Raker Act. It’s also big for PG&E at the Bucks/Grizzly complex - it’s such a large drop in elevation that each cubic foot of water makes a lot of money in electricity.