CENTENNIAL - His snowshoes crunching on the snowy trail, Bruce Boe marched steadily up the mountain.

It's about a 20-minute hike from the nearest road up to his small, lonely cabin tucked away in the forest high in the Snowy Range of southern Wyoming. He spends two weeks at a time alone here at an elevation of more than 10,000 feet all winter long in the cozy shelter that also serves as a makeshift laboratory.

Boe is the director of meteorology for Weather Modification Inc., a North Dakota-based company that seeds clouds in an attempt to increase snow or rainfall in countries around the world. He could probably have a desk job and spend more time at his home in North Dakota, but he wouldn't want to miss out on being at the center of what's considered the most exciting research project in the country in his field.

"I like to be the hands-on scientist," he said.

The Wyoming project isn't the biggest cloud-seeding operation in the world. But, scientifically, it just may be the most important.

Boe is one of several scientists working on the five-year Wyoming Weather Modification Pilot Project, an $8.8 million research program funded by the state of Wyoming. The project's scientists, along with state water managers, hope to find proof of whether the decades-old practice of seeding clouds - trying to squeeze more precipitation out of passing storms - actually works and that it's a practical option for increasing the state's water supply.

Members of the world's science community - cloud-seeing advocates and skeptics alike - are watching the project closely.

"For a scientist doing research, this is it. As far as in terms of the research, it is the biggest in the United States by far," Boe said.

There is virtually no federal funding for cloud-seeding projects and research, although several states and foreign countries invest millions of dollars into them year after year.

"There are a lot of other countries who are going after it in a big way, places like Morocco and Saudi Arabia. My two biggest projects are Wyoming and West Africa," he said.

The Wyoming project is in its fourth year, only the second winter in which cloud seeding in earnest has actually been performed. The first two years involved mostly taking measurements and weather readings, obtaining permits from the U.S. Forest Service, gathering other statistical data and getting equipment in place.

'I'm encouraged'

While Boe's company is contracted to perform the cloud-seeding operations, independent teams of scientists from the Colorado-based National Center for Atmospheric Research and the Desert Research Institute in Nevada are independently evaluating whether any increases in precipitation that occur are from cloud seeding or from just normal variations in the weather.

That's the real trick to proving if it works. Cloud-seeding scientists estimate that, if done properly, pumping silver iodide into a cloud will increase snowfall in most cases by about 10 to 15 percent. That's roughly the same percentage of natural variability possible in normal weather patterns.

It's too early to say with any certainty that Wyoming's cloud seeding is working to make more snow, but the scientists are beginning to amass a massive amount of vital information from the project. They still have much more data to collect.

They conducted 26 four-hour seeding events in southern Wyoming last winter and more than 30 this winter. Ideally, they would like to have more than 200 cases to examine by the end of the five-year project.

Boe is hesitant to say that the results of the program will definitively show that seeding increases precipitation. That's up to the independent evaluators to determine, he said. But he is, after all, a longtime believer in the science of cloud seeding.

"I can see there are things that happen," Boe said, with a wry smile. "I'm confident. From my point of view, I'd say I'm encouraged."

If the snowpack reaches well above normal levels, seeding operations would be suspended to avoid contributing to flooding or other problems, he said.

Whether seeding works isn't the only question the scientists are trying to answer.

"It's important to know when it works and when it doesn't work. The big question in Wyoming is: Will it be economically feasible to do all the time or at least some of the time?"

High in the clouds

Producing snowfall by seeding clouds is not like flipping a switch, Boe said. It's more subtle. The goal is to cause a cloud's water vapor to turn into ice earlier as it passes over a mountain, to tweak the system just enough to bring a little more snow.

"The idea is not to turn the snow on or off. It's not doubling the snowfall. It's raising it incrementally," he said. "We're just trying to give it a nudge in the right direction. We're not playing God or Mother Nature."

Cloud seeding with silver iodide has been practiced since the 1940s.

Although it's painstakingly difficult to prove that it works, the concept of cloud seeding is pretty simple.

As wind passes over a mountain range, a super-cooled cloud of water particles forms. Although the temperature in the cloud might be below the freezing mark of 32 degrees, the cloud's moisture doesn't always turn into ice, especially if the air is very clean, until it reaches the colder temperatures near the top of the mountains. Without tiny structures within the cloud to cling to such as dust, clay particles or smoke, the water particles will continue to bounce and jitter around inside the cloud until, in most cases, it reaches high up the mountain's slope where its water content will finally freeze and fall as snow.

Enter silver iodide.

Similar in structure to an ice crystal, a silver iodide solution contains tiny compounds of silver and iodine. The nearly microscopic particles also contain sodium and chlorine, or sodium chloride, which is essentially salt.

When a silver iodide solution is pumped into the cloud as it rises up the mountain slope, the water droplets crash into the tiny silver iodide particles, cling to them, freeze and grow in size, becoming heavy enough to fall to the ground as snow. Conceivably, snow begins to fall sooner and lower on the mountain than it would have without the presence of silver iodide.

"By making [ice] farther upwind, that means there's more time for growth," Boe said.

From the ground

While clouds are often seeded from airplanes, the seeding on the Wyoming project this winter is all being done from the ground by generators on 20-foot towers.

Inside a generator placed upwind, a propane flame heats the silver iodide solution, and a nozzle sprays it into the air. It rises into the cloud and is carried by the wind to a target area, which is where the scientists want it to snow.

There are eight generators in each mountain range, the Snowies and the Medicine Bows, and another seeding site on the west side of the Wind River Range that has 10 generators.

Meteorologists determine when conditions are right for seeding and tell the technicians which generators to turn on. The technicians, sitting many miles away at computers, activate the generators remotely through satellite modems.

Boe, using a machine in his cabin called an acoustic ice nucleus counter, checks the outside air during seeding operations to detect the presence of silver iodide to make sure the particles are reaching the target area.

"A lot of cloud seedings have failed because they failed to transport and disperse silver iodide to the target area," Boe said.

Checking the results

Before, during and after seeding events, the weather is monitored closely. Independent evaluation teams from NCAR and DRI check the snow for the presence of silver iodide and to collect other statistical data.

Seed generators are never turned on at the same time in both the Snowy Range and Medicine Bow Mountains - only randomly either in one mountain range or the other. The forecasters and evaluators are not told which mountain range was seeded, which should eliminate any bias in their predictions and conclusions, said Dan Breed, lead scientist for NCAR.

Seeding only one range at a time also allows researchers to collect a double dose of data from each storm - one from a seeded mountain range and one that only received natural snowfall. Comparing results between the two ranges could help determine if increases in snow were a result of seeding or that ever-elusive variability that occurs with natural snowfall.

"You're really fighting an uphill battle with natural variability," Breed said. "That's been a hard part of proving weather modification experiments, always fighting that variability."

Few winter cloud-seeding projects have been so scrutinized by independent evaluation teams. That's what distinguishes the Wyoming Weather Modification Pilot Project from most other cloud-seeding operations, said Barry Lawrence of the Wyoming Water Development Commission office, which oversees the project.

"The big difference is the independent evaluation. A quarter of the budget goes to NCAR for the independent evaluation, so you're not in a situation where the operators are evaluating their own results."

Big possibilities

Early scientific experiments with cloud seeding in the 1940s were initially so promising that many meteorologists thought they'd someday be able to turn the rain on and off.

That never turned out to be the case, but companies that conduct cloud-seeding operations claim to be able to tweak passing weather systems just enough to squeeze out a little extra rain or snow from their clouds. The technology of the science is growing rapidly, and research programs such as the Wyoming project are attempting to unlock the secrets of changing the weather.

Arid Western states spend millions of dollars a year on cloud-seeding projects.

"I don't think most people understand how widespread seeding is around the West," Lawrence said.

Weather modification techniques are also used to try to minimize the effects of hailstorms on crops and to thin fog at airports. Scientists are also looking into the possibility of weakening or manipulating hurricanes.

If it's proven that winter cloud seeding creates more snow and produces more spring and summer runoff for water supplies, the next step for Wyoming would be to determine if it's economically feasible to keep doing it.

One cost estimate anticipates that increasing water supplies by cloud seeding would cost about $8 to $15 per acre foot of water, compared with hundreds of dollars per acre foot to build new dams and reservoirs, drill new wells and divert water. An acre foot is the amount of water needed to cover one acre with water that's a foot deep.

Cloud seeding is one of many strategies the Wyoming Water Development Commission is pursuing to increase the availability of water for the state's residents, farmers and ranchers. Even if seeding is proven successful, it's not going to be the only answer for Wyoming's water needs.

Mike Purcell, director of the commission, said at the end of the five-year project it would be up to lawmakers to decide if it should continue.

"If this is shown to increase the supply by 10 percent, it would be very valuable for all types of water uses. It's going to be fun to see how this all works out," he said.

Universities join in

Does a cloud disappear when its water droplets freeze and fall as snow?

Does injecting silver iodide into a cloud create more or less snow?

If cloud seeders are successful in increasing snowfall, how much would that increase water supplies?

Those are a few of the questions students and professors at the University of Wyoming and University of Tennessee will try to answer this winter.

The Wyoming Weather Modification Project, an $8.8 million state-funded study of cloud seeding in the Snowy Range, Medicine Bow Mountains and Wind River Range, has presented the opportunity for the two universities to "piggyback" on the project with their own separately funded weather research.

Periodically this winter, UW professor Bart Geerts and graduate students will fly over snowstorms in a Kingair research aircraft as cloud-seeding experiments are going on to study how the clouds are affected.

Using technologies called cloud radar and LINAR, short for Light Detection and Ranging, the crew will take snapshots of the clouds similar to the three-dimensional slices of a medical MRI scan.

"We are basically trying to look at it in the finest detail in time and space. We're actually looking at the cloud as it is injected with silver iodide," Geerts said.

When a cloud is seeded, "The idea is that silver iodide injected into a cloud is going to turn all that liquid water into ice pretty quickly. We want to see if that really happens."

"The concept is that silver iodide will just remove the cloud, and all that's left is clear sky, and all you get are ice crystals that fall down. That's never been seen. It's never been recorded. Vapor deposits onto ice crystals that form around all these silver iodide nuclei, and we should be able to see that."

While cloud seeding is based on the theory that the presence of silver iodide particles in a cloud will increase snowfall, some speculate they could actually create less snow.

"What happens when you have too many wolf puppies and only one wolf? They're all competing for the same food. You might have a bunch of runts," Geerts said.

University of Tennessee professor Glen Tootle is leading a study on the effects of an increased snowpack on spring and summer runoff. The university experiment could determine what a small snowpack increase in the Medicine Bow Mountains would mean for the North Platte River drainage. No one knows for sure if 10 percent more snow created from cloud seeding would necessarily produce 10 percent more water for the state's supply.

"Those basic questions have not been answered," Geerts said.

- Wes Smalling