The Science of Snow: The Art of Making Snow Work 

From snowmaking on ski slopes to cloud seeding for water, snow doesn't just have to fall

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Average isn't bad for the folks at Idaho Power, but average can always be improved upon. In fact, Idaho Power has been trying to go above average since it started a regular cloud-seeding program in 2003.

By introducing silver iodide into the clouds of passing storm systems, the utility is attempting to improve the snowpack in key areas, thereby creating more runoff and more water to generate electricity in the company's hydroelectric dams.

"The more snowpack we have, especially in the higher elevations ... it's really valuable to the company," said Derek Blestrud, meteorologist with Idaho Power.

The cloud-seeding program began in the winter of 1996-1997, but because it was a heavy snow year, it only operated for one month. It wasn't until February 2003 that Idaho Power had the funding in place to start it up again.

Efforts are now focused on two areas: the Payette River Basin and the Upper Snake River Basin.

Idaho Power's program started in the Payette River Basin, where the company now has 17 remotely operated ground generators. The generators are spread in a horseshoe across the basin from the northwest to the south roughly seven miles apart to allow for targeted seeding. The company occasionally uses a plane to do the seeding when conditions are more appropriate for it.

Idaho Power also teamed up with several communities in the Upper Snake River area that had been using cloud seeding since the 1990s for irrigation. The partnership started in 2008 and it has allowed the program to grow to include 18 generators with plans for a 19th, as well as an additional 25 manual generators.

There have been a few studies on the effectiveness of cloud seeding and Idaho Power cites studies that show a roughly 5-15 percent increase in snowpack in the Payette River Basin, with an average of a 13 percent increase.

Studies on the effectiveness of the Upper Snake River program are still in the works, although there is an ongoing $13 million research project in Wyoming looking to better quantify the effects across three mountain ranges there.

Last winter Idaho Power spent roughly $1 million on the cloud-seeding program, and while that may sound like a lot to invest, Blestrud said the cost-benefit ratio is between 3-1 and 4-1, adding that company estimates show that the program adds roughly 200,000 acre feet of water to the system. That amount can generate roughly 100,000 megawatts of electricity, enough to power an estimated 7,900 homes.

Cloud seeding is not snow making, Blestrud cautioned; it's working with what nature already provides.

When a storm system comes across Idaho and into the West Central Mountains, Idaho Power meteorologists look to see if it meets the criteria they're looking for, then they target the layers of super-cooled water within the clouds.

The generators or plane then introduce silver iodide to super-cooled water--liquid water that is between -5 and -15 degrees Celsius--to encourage it to start freezing and drop out of the cloud as snow.

When cloud seeding started, dry ice was originally used to start the freezing process. Then scientists discovered that on a molecular level, silver iodide actually looks like an ice particle and makes a good seeding agent. These days, there are four different types of cloud seeding: winter, like what Idaho Power is doing; hail suppression, which is used most commonly in the Plains; rain enhancement, which is a byproduct of hail suppression; and fog suppression, commonly used at airports to improve visibility.

Idaho Power is one of only a few power companies utilizing cloud seeding as a tool. In fact, according to the National Oceanic and Atmospheric Administration, in 2001 only 66 cloud-seeding projects were operating in the West.

Idaho Power officials are quick to point out that increased snowpack not only benefits the utility company, but it means there's more water for all water users, be they irrigators, recreationists or fish and wildlife.

Idaho Power started its annual program Nov. 1 and will run it through the end of April 2013, depending on what Mother Nature adds to the mix.

But Blestrud is careful to add that snow doesn't come from every storm--it has to be the right storm.

"When it's a thick, deep storm and it's cooler, we can do a lot with that," he said. "[Cloud seeding] can't offset a drought--we can't seed if the clouds aren't there."

Forecasting what nature is going to do is the purview of the National Weather Service. Each day, the Boise office releases a weather balloon to get a better picture of what's happening above the surface. Combine that info with numerical weather prediction models and it helps meteorologists understand the larger patterns.

Breidenbach said that while the most accurate predictions are only a few days out, longer-range predictions look at weather on a seasonal level.

This year has kept officials on their toes. A few months ago all, indicators pointed toward an El Nino winter, when warmer equatorial ocean conditions lead to a drier, warmer winter in Idaho. But over the last several weeks, it appears as if the ocean isn't going to warm as much as expected, keeping water temperatures near normal and creating what is called a neutral year.

"The dice are equally weighted at this point," Breidenbach said.

If it is in fact a normal winter, Boise could receive roughly 20 inches of snowfall over the season.

Of course, what is considered normal is changing this year. Percent of normal is measured in comparison to the past 30 years--but that 30-year period changes every 10 years. This year marks just such a shift, meaning the snowpack will be compared to the snowfall between 1981 and 2010 rather than 1971 to 2000, as it was last year.

Abramovich said that means the relatively wet 1970s will no longer be used as a comparison but the dry 2000s will, which affects the percent of normal statistic. For example, the Bigwood Basin finished the 2011-2012 winter with slightly below normal snowpack, but that same snowfall would be considered slightly above average this winter.

October's early snowfall was welcome by more than just ski areas. Abramovich said record-low rainfall in August and September makes a good snowpack even more important.

"After the long, dry summer, there's a big deficit in the soil moisture," he said. "Fall rain helps fill the void and prime the soil for next year's runoff."

Abramovich and the NRCS crew will be carefully watching the snowpack monitoring sites--known as SnoTel sites--measuring snow not only in inches but in snow water content, or the amount of water in the snow that will melt into runoff. In a typical year, Bogus Basin receives roughly 260 inches of snow and has a 10 percent water density, which means all that snow melts down to 26 inches of snow water.

The higher the elevation, the more precipitation and the colder the temperatures (roughly 3 degrees per 1,000 feet), meaning that a location like nearby Trinity Mountain, which sits at 7,700 feet, compared to Bogus Basin's 6,340 feet, gets roughly 380 inches of snow a year.

While reservoirs were drained to meet irrigation demands because of the extremely dry summer, Breidenbach said normal snowpack would be enough to refill the area's reservoirs. That is, as long as the snowpack doesn't melt as fast as it did last spring when sudden warm temperatures meant so much runoff water hit at once that reservoirs had to release some of it.

"That's why we depend so much on our winter snowfall," Abramovich said.

But when it all comes down to daily life, most skiers are simply hoping that they can make the snow work for them this winter by taking advantage of a long ski season. For them, Abramovich suggests a new favorite number: 41.

"Forty-one is the key number in Boise," he said. "It has to be at least 41 degrees in Boise to snow at Bogus."

Need some help planning your winter adventures? Download your own copy of the Northwest Mountain Guide by clicking here.

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