Nevada State Cloud Seeding Program
Researchers gear up to get the most out of winter

Hopi shamans of the American southwest had a special ceremony for coaxing water from desert skies. Their rain dance involved snakes, body paint and some strong magic. In the modern American West, there’s another method commonly used, requiring fire, a few special chemicals and some sound scientific principles. It’s DRI’s Nevada Cloud Seeding Program, and no, it doesn’t exactly qualify as an ancient ritual. But considering the program has been in operation for more than 20 years, it’s at least a long-standing tradition.

Preparing for another winter season. DRI Instrument and Field Technician II Bryan Loss, below, and Field Technician Jeff Dean, on the burner tower, set up a DRI cloud-seeding generator on a ridge about 7 miles west of Lake Tahoe in late August. The generator can be controlled by computer and has enough fuel to operate for 11 full days of seeding before the crew must ride snowmobiles up to service it.(Photo by John Doherty)

Tradition with a goal, that is. In much of Nevada, the driest and fastest growing state in the union, communities large and small rely on the quiet accumulation of wintertime snow in mountain watersheds to feed the rivers, streams and reservoirs that support their burgeoning communities. Cloud seeding, by releasing particles of silver chloro-iodide into winter clouds, helps along the natural process of snow formation. With some careful targeting and a little luck, snow will fall in west and central Nevada’s all-important mountain watersheds, increasing the snow pack and, ultimately, the water supplies of the communities, farms, lakes and sensitive habitats of the surrounding areas.

If the idea of changing the weather sounds futuristic, consider that weather modification research began as far back as 1946 and is currently used around the world to augment water supplies, disperse airport fogs, even lessen the destructive force of hailstorms.

“DRI’s research into cloud seeding began, well, about the same time DRI did,” says Arlen Huggins, director of the Nevada State Cloud Seeding Program. Established in 1959, DRI began its first cloud seeding research two years later. And, Dr. Patrick Squires—a man credited with participating in a 1947 Australian cloud seeding experiment that was the first to produce rain reaching the ground—headed its Laboratory of Atmospheric Physics. One of DRI’s earliest seeding ventures was the Pyramid Lake Project, a federally funded operation to determine whether cloud seeding would help raise the lake’s water levels. While seeding wasn’t the answer to that problem, the study showed it was a cost-effective means of augmenting the water supply. Research continued, eventually leading to the current state program, which has been in continual operation since 1984. This year the program will operate a total of 19 remotely controlled ground-based generators in the Tahoe–Truckee basin, Walker and Carson River basins, and the Ruby, Toiyabe and Tuscarora mountains.

Built from scratch in DRI’s shops. Bryan Loss gives finishing touches to the leveling posts on one of three new cloud seeding generators he has constructed from the ground up at DRI’s cloud seeding facilities at the Reno-Stead Airport. The steel boxes, and the equipment inside and mounted on a rooftop tower, must be rugged enough to endure the full force of winter snowstorms.(Photo by John Doherty)

When winter storm conditions are right, those generators are signaled via radio or cell phone to start burning a solution of silver iodide, sodium iodide and salt in acetone to release silver chloro-iodide particles into the clouds above. Introducing these particles helps turn the cloud’s water drops to ice crystals that can then form snow. Of course, clouds can make snow without help from us. “Some clouds convert liquid to ice very effectively,” Huggins explains. “Very often there will be a higher colder cloud above a lower warmer one, and as ice crystals descend from above, they sweep out the water from the clouds forming close to the mountain. We call them natural seeders.” Silver iodide particles are most effective when these “seeder” clouds are lacking, getting water from clouds that would have otherwise yielded very little, or squeezing a bit more from those already disposed to drop flakes.

Sometimes, though, more snow isn’t desirable, so the program has a strict set of criteria for suspending operations. Seeding stops, for example, when avalanche danger in an area is extreme, when weather conditions might lead to flooding and during major travel periods like Thanksgiving and Christmas. “Above-normal snow accumulations would also suspend seeding operations,” Huggins says, “but unfortunately that hasn’t happened very often in the last few years.”

With water in the West in such demand it’s natural to question whether making snow in one place keeps it from falling in another just as eager to have it. Huggins sighs before addressing this apparently common concern. “The simple answer is ‘no, it doesn’t.’ For one thing, storms don’t move in straight lines and they’re constantly evolving. Clouds being seeded in the Lake Tahoe area, for example, are not likely to have much effect on the weather in central or northeast Nevada.

Experimental mountain weather remote sensing efforts in the “early days.” Looking like a frosted garbage truck, this weather radar van was parked on a peak in the Squaw Valley Ski Resort in the late 60s and early 70s to detect cloud moisture and reveal precipitation patterns. The van was involved in a major, six-year study of the feasibility of using cloud seeding to stabilize the level of Pyramid Lake. The study concluded that cloud seeding wouldn’t maintain Pyramid Lake, but it would be a cost-effective means of increasing winter snow packs.(DRI file photo)

“Their better storms often come on a different track and are usually not the same ones that do well over the Tahoe area,” Huggins says. Then, he explains, you’ve got to take into account the size of a storm system. “The available water budget in any winter storm is enormous. There is mostly water vapor, as well as ice and a relatively small amount of liquid water. Seeding only affects the liquid water, and only in a very small area as compared with the huge area covered by the system. Even if our seeding were 100 percent effective, it would change the overall water budget of the storm less than one percent.”

In short, seeding has little to no effect on regional weather patterns but can have a considerable effect on the snowfall in a specific area. Just how much of a difference does it make? The answer depends, of course, on what nature provides—no storm clouds mean no cloud seeding. A heavy winter obviously provides more opportunities for seeding, resulting in more acre-feet of water for that year. Estimates of extra water produced from seeding have varied from 20,000 to 80,000 acre-feet over each of the last 10 years. And, while the total amount of water produced from seeding is obviously less in dry years, it can still translate to an economic benefit for users. “In a drought year, seeding may mean extending the season just enough for one more cutting of alfalfa,” Huggins says.

That alfalfa might be grown in Nevada’s Mason Valley, where the Walker River Irrigation District is an active and enthusiastic supporter of DRI’s cloud seeding program. In this important agricultural area, farmers, environmentalists and sportsmen vie for the limited water of the Walker River that is crucial to not only the alfalfa and onion growers, but also to the survival of Walker Lake, which supports fisheries, recreationists and the economic viability of nearby towns. “We got to the point,” WRID Manager Ken Spooner says, “where we felt the need to do everything we could to help the basin. We did some research, got informed and decided to dedicate funds to this system, and to DRI, because we all know this is their forte.”

For the past two years, WRID has supported the program by financing the construction, installation and operation of the area’s seeding generators, and the agency recently joined forces with DRI in securing a Bureau of Reclamation grant to conduct effectiveness studies in the basin. Atmospheric models will simulate the dispersion of seeding material over the basin and chemical tracer studies will verify its presence in the snow pack. Hydrologic modeling will estimate seeding’s impact on the river system. “It’s great,” Spooner says, “to have the opportunity to work with the folks at DRI, and I really think that what we create here in the Walker Basin can ultimately be extrapolated to other parts of Nevada.”

The State of Nevada Weather Modification Program areas. Program Manager Arlen Huggins supervises the seeding activities in five project areas, each with its own set of challenges but with a common need for more water. The map colors indicate the average annual precipitation, with the seeding areas focusing on mountain watersheds where precipitation is the highest (blue-green).

In addition to the purely practical goal of providing water to a thirsty state, the program also provides an opportunity for ongoing research to improve not only operations, but also to better understand the atmospheric processes at work—these people are scientists, after all. “We are always trying to piggy-back research with operations,” Huggins says. “One benefits the other.” Over the years, research has led to several improvements, including faster-acting seeding materials that work at a broader range of temperatures, and the ability to detect the presence of liquid water in clouds from the ground without costly aircraft flights. Researchers are also now able to use atmospheric modeling—computer simulations of atmospheric processes—to look at how seeding materials are transported during different types of storms and at different times during a storm. “There is a huge variety of storm-types that cross the Sierra during a season. The models let us look at them without waiting for them to actually happen, and help us get the placement of generators correct. It’s very valuable to the program.”

And so, while ordinary “traditions” stay the same from year to year, Huggins sees to it that the Nevada Cloud Seeding Program is constantly being improved. “We’re always looking for an edge in terms of tricks, new things to apply.” That’s why 20 years later, the program continues to benefit Nevada.

—Jackie Allen