Another in a continuing series of powerful storms will hit Southern California this weekend with gale-force winds and up to 20 inches of rain in the mountains, posing a major threat of mudslides and flooding, meteorologists said Wednesday.
The storm is expected to invade the Southland in three waves -- on Friday, Saturday and the third on Sunday night. Each successive wave will increase the likelihood of mudslides and flooding on fire-denuded hillsides and lowlands already saturated by record rainfall.
The storm is much warmer than its predecessors, exacerbating the problems, the meteorologists say. Heavy snow that fell earlier is likely to melt, adding to the runoff.
“If this were a football game, it would be called piling on,” said William Patzert, a meteorologist at the Jet Propulsion Laboratory in Pasadena. “There’s a high probability of mudslides and flooding, and our storm drains will flush out into the ocean, contaminating our beaches.”
Throughout the Southland, fire departments were distributing sandbags and helping homeowners build protective berms.
Los Angeles has received 15.68 inches of rain since July 1, the beginning of the rainfall season. That’s almost four times the normal rainfall for the date, and more than the city usually receives in an entire year.
Patzert said the spate of rainy weather is being caused by a shift in the path of high-altitude jet stream winds that circle the globe.
“Normally, these winds head from west to east across the northern tier of states,” he said. “But this year, it’s a jet stream on steroids, pushing the storms south along the coast, picking up moisture along the way.”
These storms have been turning inland across Southern California. When they squeeze up against the mountains of Santa Barbara, Ventura, Los Angeles and San Bernardino counties, the moisture is carried aloft, where it condenses and falls as heavy rain and snow.
“It seems an awful lot like Seattle, doesn’t it?” said Scott Holder, a Ventura County hydrologist. “We’re waiting for a Starbucks to pop up on every corner.”
National Weather Service forecasters said the coastal valleys should get 4 to 8 inches of rain over the weekend, with up to 20 inches in the mountains. They said the rotating storm would strike the Southland with successive waves of precipitation, like the spokes of a spinning wheel.
The first wave is expected to hit the Los Angeles area Friday afternoon, “a 3- to 6-hour burst of very heavy rain, with showers behind it,” the weather service said. “Rainfall rates could be more than an inch per hour in some places.”
Forecasters said the rains would be driven by winds moving up to 55 mph.
Saturday morning should be relatively dry, before the second wave moves in.
“As this next wave is arriving, the air mass will be warming, as the source of the moisture becomes more subtropical,” the weather service said. Typically, when this happens, rainfall increases dramatically.
Heavy rain is expected Saturday night and into Sunday morning. Forecasters said this relatively warm rain would cause the snow level to rise from 4,000 to about 8,000 feet by Sunday morning. The snow, up to 3 feet at lower levels, will melt rapidly and vastly increase the storm runoff.
“There is a potentially very critical hydrological event over the area,” the weather service said. “All signs point to a very wet period with the potential for lots of flooding problems.”
In San Bernardino County, officials were keeping a close watch on Waterman Canyon and Devore, where 16 died in mudslides and flooding in December 2003.
In Malibu, Los Angeles County Fire Capt. Bob Goldman said a swift-water rescue team would be on call 24 hours a day in case anyone is swept into a flood-swollen stream or flood channel. Deputies said there was potential for damage along the coast from 7-foot tides and ocean swells generated by the storm.
Officials said hillsides scorched by wildfires in the last couple of years in Los Angeles and Ventura counties were especially susceptible to flooding. Goldman said the flames left a waxy covering on the soil that makes it difficult for water to seep into the ground.
“We’re anticipating more runoff, more erosion and more rock slides,” he said.
In Glendale, Fire Capt. Matt Luchetta said sandbags were being used to build barriers around many homes.
“We’ll help them shovel in the middle of the night if we have to,” he said.
In Riverside County, officials warned that flash floods could send walls of water down washes that were dry moments earlier.
“If you see a ‘Do Not Cross’ sign, don’t try to cross it,” said county fire spokesman Patrick Chandler, “even if you’re driving an SUV.”
Officials warned that more rocks and dirt may tumble onto Highway 243 near Idyllwild after a rock slide closed the road Tuesday morning.
Forecasters said the precipitation should slacken Sunday afternoon, picking up again Sunday night with the arrival of the third wave of the storm. The rain is expected to continue through Monday, with the snow level dropping back to about 5,000 feet as cold air moves in. There are chances of rain and snow showers Tuesday and Wednesday.
Despite the record rains, there won’t be enough to end a drought in the Western United States that began more than six years ago, Patzert said.
“About 80% of the rain that falls runs out to sea,” he said. “So it takes three to four years of above-average precipitation to end a drought. There’s no quick fix for a drought.”
Times staff writers Kay Saillant and Lance Pugmire contributed to this report.