Let it snow

Cold front smacks against warm. Storm clouds move in, gray overtaking blue, moving in a mass. The chill in the air crystallizes. Rings of clouds wrap the mountains, cutting charcoal smudges across their peaks. The snow begins to fall. As it does, if the conditions are right, scientists—sometimes on the ground, sometimes in an airplane—may be doing a technical, scientific, snowy version of a rain dance.

Wintertime cloud seeding is a way to modify the weather by adding a seeding agent, silver iodide, to certain clouds to encourage snow fall.

“Some parts of the storm, the natural precipitation process is somewhat inefficient,” says cloud seeding program director Arlen Huggins of the Desert Research Institute. “It lacks the particles ice can form on. Without these particles, whether they’re natural or added through cloud seeding, the cloud droplets would stay as water and basically ride over the mountain and evaporate on the downwind side without forming precipitation.”

Cloud seeding has been practiced in the United States for more than 50 years. In October, the Desert Research Institute earned a $155,000 grant from the Truckee River Fund for cloud seeding projects in the Tahoe-Truckee area, Walker River Basin and the Ruby Mountains.

It’s done by dissolving the silver iodide in a solution of acetone and spraying that solution into a flame, says Huggins. That vaporizes the liquid, leaving behind a fine smoke plume of billions of silver iodide particles. These are carried by the wind toward a target area to give snowfall a boost.

While increasing area snowfall—and therefore local water—is something few would argue against, the idea of adding chemicals into the air to do it may raise some eyebrows, especially considering that the Environmental Protection Agency regards silver iodide as a hazardous substance, a priority pollutant and a toxic pollutant.

Huggins says it’s only hazardous if the concentration is high enough. He says DRI has taken snow samples from their seeding areas to see if they could detect silver in the snow that would be higher than the natural level of silver in snow, and they haven’t.

“The bottom line is all the water samples, soil samples we take from our downwind area, we find concentrations that are more than 100 times less than what’s considered toxic to plant or animal life,” says Huggins.

Cloud seeding isn’t to be confused with geoengineering, which is weather modification on a global scale—and a contentious issue currently under debate. And while published scientists tend to agree that cloud seeding is effective, it’s not an answer to climate change issues, and is only a small part of the solution when it comes to water resource problems.

“Cloud seeding for snowfall is not something you do to get yourself out of a drought,” says Huggins. “It’s something better done during a normal year when you have a normal frequency of storms and can add to the water level of storms throughout the season—helping water storage in years when you’re getting some precipitation rather than react to it when your reservoirs are dry. … They’re all small solutions to a big problem. When there’s declining water in [a reservoir] when it’s been dry for decades, there’s little you can do to try to change the supply side of that situation.”