MODESTO, Calif. -- Pilots Brandon Thurston and Artie Cifarelli can see their destination even before their twin-engine Cessna leaves its Central Valley hangar: the foothills of the white-topped Sierra Nevada.

Thurston jokes that he's responsible for all the snow clinging thick to the distant peaks. But as an employee of Weather Modification, Inc., which is based in North Dakota, what he says is not entirely untrue.

The two airmen have made about three dozen flights from the Modesto City-County Airport to the high country in recent months, ``seeding'' clouds so they'll produce more snow. The end goal is more water for drought-stricken reservoirs that provide not only for the communities of the valley, but also for the Bay Area.

``For a while, we were flying much of the night,'' said Thurston, 27, who left his home in Trinidad, Texas, late last year for the busy winter cloud-seeding season in the Sierra. ``We were going to bed at 6 in the morning and waking up at 2 in the afternoon.''

Efforts to make snow and rain virtually out of thin air were once the realm of science fiction. Even today, they're dismissed by some as fanciful and hardly worth the time. But after four historically dry years in California, the practice has been on the uptick.

The stormy skies that came with this year's El Nino provided ideal conditions for cloud seeding, which requires enough water vapor in the air so that the introduction of chemicals like silver iodide can coax the clouds to crystallize and send droplets to the ground.

From San Francisco's Hetch Hetchy watershed to the East Bay Municipal Utility District's Mokelumne River to the coastal mountains in Southern California, water managers say cloud seeding is boosting precipitation -- sometimes by 10 percent or more. Many say that alongside this year's slightly wetter winter it's been essential to riding out the drought.

``Some people used to think of it as smoke and mirrors,'' said Jason Carkeet, a utility analyst for the Turlock Irrigation District who hired the cloud-seeding company at the Modesto airport. ``But it seems to have gained more acceptance. There are fewer and fewer districts that don't have a program.''