With at least five generators around the Lake Tahoe basin cleaned and ready, officials at the Desert Research Institute waited Friday for the temperature to drop below 32 degrees before they let their cloud-seeding guns rip.
Cloud seeding has been conducted in the Tahoe area since the 1960s and DRI, an arm of University Nevada, has designed and operated the Nevada state program since its inception.
"Cloud seeding is not going to make a phenomenal increase in water content, but it is a very cheap, cost-effective way to increasing water resources," said John Doherty, DRI director of public information.
Ground-based generators are used to burn a solution of silver iodide-sodium iodide and salt in acetone to release silver chloro-iodide particles that make ice crystals which turn to snow.
Weather conditions are selected to optimize fallout in targeted basins.
"It's a matter of it getting cold enough for it to be effective," Doherty said.
Generators are remotely operated by radio or cellular telephone. A seeding aircraft is at times used to augment ground-seeding operations. The aircraft releases an iodide-sodium solution from pyrotechnic flares or solution burners.
DRI is staffed by three full-time technicians who install and maintain all generator networks and two part time professionals who forecast seeding operations, implement design changes, evaluate operations, monitor environmental aspects of the program and evaluate seeding effectiveness.
The benefits of the five seeding generators, may seem rather small, with precipitation increases recorded to be between 0.1 to 1.5 millimeters per hour. Each generator has about an eight-mile radius, Doherty said.
Estimates of augmented water from seeding have varied from 20,000 to 80,000 acre-feet annually. Seasonal percentage increase estimates range four to 10 percent more water in drought years.
The cost of augmented water, based on the cost of the program, has ranged from $7 to about $18 per acre-foot, Doherty said.
"Every storm is different and every precipitation amount is different," he said. "If you look at it as eight square miles for each generator getting a millimeter increase of snow an hour, that's enough to fill quite a few bathtubs."
INFORMATION
For cloud seeding updates, log on to http://cloudseeding.dri.edu/