Water agencies across the West, including in Southern California, have for decades shot silver iodide into clouds from cannons and airplanes. The theory is that the particles make the clouds drop even more snow than would fall otherwise. But there is very little scientific evidence that it works. “You do get the question, how much snow did we make? I can’t really tell you. I don’t really know.” said Chris Harris, executive director of the Colorado River Board, a California state agency that represents Southern California water agencies on Colorado River issues and spends up to $250,000 annually on cloud seeding in the Rocky Mountains.