Storm May Yield Hail, Waterspouts

A flash-flood watch was issued for the burn areas of Los Angeles, Ventura and Santa Barbara counties, and forecasters warned of heavy rain, lightning, hail and waterspouts as a powerful storm system began moving into Southern California late Tuesday.

The National Weather Service said the rain should continue, off and on, through Friday, with up to 2 inches in the coastal valleys and as much as 4 inches in the foothills and mountains.

“We could be in for a big event,” said Bill Patzert, a climatologist with the Jet Propulsion Laboratory in La Canada Flintridge. “A cold storm that had been sitting off the coast has been picking up subtropical moisture and intensifying, and now the jet stream has grabbed it and is pushing it all into Southern California.”

The heaviest rain is expected today and tonight along and above hillsides stripped bare by the September wildfires.

“Especially prone to flooding would be the Topanga, Harvard, Gorman and Tovey burn areas,” the weather service said in an advisory issued Tuesday morning. “Residents near and downstream of the burn areas need to be prepared to take protective action.”

Forecasters said other danger spots included the Gaviota burn area in Santa Barbara County, where runoff could flood Pacific Coast Highway.

“Some thunderstorms could produce small hail,” the weather service said. “Due to the vigorous upper-level circulation, [we] cannot rule out localized rotation in the form of waterspouts or small tornadoes.”

Patzert said the core of the storm was a “cutoff low,” a cold low-pressure system that moved south along the coast before stalling off Southern California.

“It’s been dragging in moisture that trails all the way to Hawaii,” he said.

By Tuesday afternoon, he said, high-altitude jet stream winds that encircle the Earth had seized the storm and begun nudging it inland.

Rain started falling in San Luis Obispo, Santa Barbara and Ventura counties by early afternoon.

“It’s moving in slowly,” Patzert said. “There will be heavy rain at times, and even some hail. We could get 48 to 72 hours of pretty dramatic weather.”

Forecasters said skies should begin to clear Friday night, with warmer temperatures and mostly sunny skies Saturday through Tuesday.