Here’s a background piece on cloud seeding in southwestern Colorado from Kristen Plank writing for the Cortez Journal. She has written a nice primer on the subject also. From the article:
[Larry] Hjermstad, founder of Western Weather Consultants LLC, seeds locally for approximately 10 different entities that support the cloud seeding program, from the town of Telluride to the Dolores Water Conservancy District.
The DWCD invests in two of Hjermstad’s cloud seeding programs in hopes to increase inflow into McPhee Reservoir. Mike Preston, manager for the DWCD, said the water district has played a part in the program since 2000, and paid approximately $17,000 for the 2008-2009 winter program. “Ski areas are investing in the program for the snow to ski on, but our interest is pure and simple,” Preston said. “If we can increase the inflows into the McPhee Reservoir by some percentage, then everyone benefits.”[...]
Hjermstad recounted an independent study done by Bernard Silverman, prior chief scientist with the U.S. Bureau of Reclamation, that showed the effects of a 33-year cloud seeding program on Vail’s surrounding streams. The study, lasting from 1977 to 2005, showed an eight to 30 percent increase in stream flows. “(Silverman) wasn’t looking at snow as being of value, but rather water as being of value,” Hjermstad said. “The study verified that precipitation increases are reflected in stream flow increases. To me, this is the missing ‘ground link’ for what we are trying to do with precipitation.”[...]
Cloud seeding, or weather modification practices, is a popular process throughout the world. Locally, a total of 34 “ice nuclei” generators are spread across the San Juan Mountains, working from November through the end of March. Hjermstad will have operators turn on generators for roughly 24 storms during a three-month period.
Well over a trillion seemingly invisible silver iodide nuclei will work their way into the bottom portion of a cloud system, where they will attract moisture, produce snowflakes and fall to earth. The compound works so well at producing additional snowfall because of its nearly identical characteristics to an ice crystal. It’s as safe as one, too, Hjermstad said. “One reason silver iodide was chosen was because, as a molecule, it is extremely tightly held together once the two elements combine,” he said. “Nothing in nature breaks it apart.” This includes the sun, the photosynthetic process in plants, or anything from the digestive systems of humans, animals or aquatic wildlife. Hjermstad said that cloud seeding programs also do not take away from any precipitation that may have been dispersed into towns downwind.