Clouds over Los Angeles County were seeded with silver iodide to increase the amount of rainfall during Monday's storm, marking the first cloud seeding done by the Department of Public Works since 2002.
Los Angeles County has used cloud seeding to boost water supplies since the 1950s, backing off in times of heavy rain or when wildfire devastation creates an outsized risk of flooding or debris flows.
A 2009 cloud seeding contract for services was terminated after the Station Fire, which burned roughly 250 square miles of the Angeles National Forest. Then, last October, the state's severe drought led the county Board of Supervisors to approve a new one-year contract with Utah-based North American Weather Consultants for as much as $550,000 a year.
This week's storm offered a good opportunity for "the first go-round for cloud seeding" this season, Department of Public Works spokesman Steve Frasher said.
North American Weather Consultants has set up land-based generators in 10 locations between Sylmar and Pacoima, Fraser said. Only some of those generators were used Sunday night, as weather conditions were not ideal in all areas.
The generators shoot silver iodide into the clouds, creating ice particles. Water vapor freezes onto those particles, which fall as rain.
Cloud seeding cannot create clouds, but it increases the amount of rainfall from existing clouds. That storm water is then captured in dams and in the Pacoima, Big Tujunga and San Gabriel watersheds.
The county estimates that seeded clouds produce about 15% more rainfall.