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Pilots brave winter storms in cloud seeding program
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Turlock Irrigation District cloud seeding program planes are designed to fly in extreme weather, with heated props and de-icing equipment across the body. - photo by Photo Contributed

When winter storms force most small planes to land with iced-over wings, it’s time for these pilots to take off and fly straight into the storm.

The Turlock Irrigation District’s cloud seeding program, now entering its 22nd year, sees daredevil pilots fly specialized planes into the heart of violent winter storms, in hopes of creating more precipitation.

The plane is designed to fly in extreme weather, with heated props and de-icing equipment across the body. But there’s still an element of danger involved, said Turlock Irrigation District Utility Analyst Jason Carkeet.

“Usually, these guys are young with no families,” Carkeet said. “It’s kind of a cowboy thing to do.”

The plane departs from the Modesto Airport and flies through storms near Sonora, flares blazing from the wings. As wings become too icy, they avoid the storm for a brief respite, de-ice, and head back into the thick of things.

It’s those flares – like standard road flares – which do the heavy lifting of cloud seeding. As flares burn, they emit an ash of silver iodide. The crystalline ash molecules bond to ambient water, creating snowflakes.

The levels of silver iodide generated by cloud seeding are extremely minimal, and not detectible in runoff without the use of advanced spectrometry equipment. The project passed state environmental review in 1990.

Cloud seeding doesn’t work just anywhere, only on so-called “super-cooled water,” which has a temperature below freezing, but is suspended as humidity in the air. The super-cooled water would otherwise remain as humidity without the cloud seeding.

“It needs something to start its crystallization process,” explained Carkeet.

Normally, this super-cooled water is not visible to the naked eye. It’s the same type of water which most often becomes visible as rime ice, those wispy, wind-swept icicles which trail off tree branches.

Cloud seeding cannot make snow from nothing. Pilots work with meteorologists to identify patches of super-cooled water using radar, and looking for signs of rime ice on other planes as a sign of good conditions.

“We’re not making a storm,” Carkeet said “We’re making a storm more efficient.”

Carkeet admits it’s difficult to quantify the exact impact of the district’s weather modification program. It’s impossible to scientifically measure; there’s no way to know exactly how much precipitation would have come from an un-seeded storm.

“It’s controversial,” Carkeet said. “A lot of people say it’s all smoke and mirrors.”

But utilities across the nation – and the world – engage in cloud seeding, saying the benefits are real.

Pacific Gas and Electric, Southern California Edison, and the Sacramento Municipal Utility District are among those seeding in California alone. Most of the Sierra Nevadas are now covered by a cloud seeding program, with some programs dating back to the 1960s.

In total, the cloud seeding program costs TID and the Modesto Irrigation District, which shares ownership of the Tuolumne River watershed, about $170,000 per year. The cloud seeding is performed by Weather Modification Inc., a Fargo, N.D. based company.

The program more than pays for itself, Carkeet said, factoring in both the additional water and the electricity production from hydrogenation at Don Pedro Reservoir.

TID studies estimate that the cloud seeding produces a 2 percent annual increase in total precipitation. That’s a conservative estimate, staff said, with some studies suggesting a 5 to 10 percent boost from cloud seeding.

In an average year, that 2 percent increase translates into 40,000 acre-feet of water produced by cloud seeding, enough to fill Turlock Lake.

Already this year, the cloud seeding program has made three flights since its Dec. 1 start. By the March 31 end, dozens of could seeding trips will have occurred.