But the program is growing in the Upper Snake region, an area that drains through 15 of the dams. About the same amount of iodine is used there now, too. Parkinson figures that a full build-out in that region and the Payette region would yield about 65 ground generators, an effort they are actively working toward.

Huggins says that advances in instrumentation, numerical modeling and trace chemical analysis have improved evaluation of seeding projects and generated more excitement about growth.

During the Idaho program, Parkinson says the only time they have curtailed cloud seeding efforts during the stormy months was when the snowpack was reaching a "suspend" level, so as to not increase flooding or avalanche worries. "The years that are best for seeding are actually your average years to slightly above average years to bring in a little more water for your reservoir system to try to keep them fuller than they would naturally," Blestrud says.

At this point, the cloud seeding program can't grow fast enough to suit the utility. "If we are not in 'suspension criteria,' we do whatever we can to build snowpack," Parkinson says. "We haven't bumped into any scenarios where it is not cost beneficial."

This file was updated Jan. 10, 2013, tp correct two errors in the original story. The substance used in cloud seeding is silver iodide, not silver iodine, and the Idaho Power water resources leader is Shaun Parkinson, not Shawn Parkinson.