Scientists observe cloud seeding for the first time ever

For the first time ever, scientists in Wyoming have observed the magical-sounding practice of cloud seeding.

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. “Over time it’s something we’ve learned that we believe.”

But for Jeffrey French, an atmospheric scientist University of Wyoming, belief is not good enough.

“I think as we look towards the future, and as we know water is only going to get more expensive and harder to come by in the West, I think it’s incumbent upon us to answer the question of whether it does work, how well it works, and under what conditions it works.”

So last year, he and his colleagues made the first step towards answering that question: simply observing the process. Their results were published this week in the Proceedings of the National Academy of Sciences.

A mobile doppler weather radar based at a mountain top location during the cloud seeding experiment.

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Courtesy Jeffrey French

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Last winter, the researchers dropped silver iodide into clouds above the mountains in Idaho, and then flew airplanes back and forth inside the clouds. They were able to observe super-cooled water inside the clouds form ice crystals around the silver iodide particles, then grow large enough to fall out of the cloud as snow — something that French said hasn’t been documented before both because of the difficulty of the process and the lack of research funding.

“You’re trying to measure ice crystals from an aircraft that’s flying through the clouds at a couple of hundred miles per hour,” he said.

Although French's study was in Idaho, his work matters because Southern California gets a third of its water from the Colorado River, which has its headwaters in the Rocky Mountains. So any cloud seeding done there can mean more, or less, water for residents of Los Angeles and other cities.

Studies into the efficacy of cloud seeding have been inconclusive. A 2014 study done over the course of six winters in Southern Wyoming found only a three percent increase in precipitation over the course of the study period. The number was so low because most winter storms didn’t bring the types of clouds most conducive to seeding.

French hopes his study will give water managers detail into when it’s most effective to do cloud seeding.

“It’s not going to be the same in every cloud,” he said.

Still, the practice will likely continue in Southern California, where it’s been undertaken by local agencies like L.A. County Public Works and Santa Barbara County Public Works, because it’s viewed as a cost effective way to increase the amount of water coming into a river basin. According to L.A. County Public Works, which did cloud seeding in the San Bernardino Mountains most recently in 2016, water created by cloud seeding is 83 percent cheaper than purchasing imported water from the Metropolitan Water District.

This post was updated to reflect when L.A. County Public Works conducted cloud seeding.

This story is part of Elemental: Covering Sustainability, a new multimedia collaboration between Cronkite News, Arizona PBS, KJZZ, KPCC, Rocky Mountain PBS and PBS SoCal.