A rain storm is expected to pass through Southern California starting Thursday afternoon that will last through Friday.
Some areas are expected to receive up to 2 inches of rainfall, with potentially significant episodes of heavy downpour mainly on Thursday night in Ventura and L.A. counties, Carol Smith with the National Weather Service told KPCC.
The San Gabriel Mountains are expected to see up to 3 inches.
"It's certainly not a drought-breaker, but it is going to be a good rain event with periods of heavy rain," Smith said.
So far this year, Southern California has only captured about 48 percent of what it normally would during a regular storm season, according to Kerjon Lee, a spokesman for the L.A. County Public Works Department.
"Water conservation in Southern California is a way of life now. It's not just a drought issue," Lee said, adding that the county is eager to capture as much water from this storm as possible.
The city’s winter shelters will be open 24 hours a day starting Thursday through Saturday morning, Tom Waldman, director of communications for the Los Angeles Homeless Services Authority, told KPCC. The approaching storms are serious health and safety hazards for people living in the streets, under freeway overpasses and in riverbeds, he said.
Outreach coordinators from LAHSA were out Wednesday afternoon delivering fliers with shelter contact information, Waldman said. The hardest part of LAHSA’s job is convincing people to take shelter when it rains, he said.
“When the weather is bad its best for their health to be inside,” Waldman said. “I know that message sounds obvious but there’s people in the streets and riverbeds — for whatever reason — don’t feel comfortable in a shelter. We have to emphasize it with more momentum.”
Heavy downpours also bring the risk of flooding.
"With heavier rain rates, you could get some localized flooding, just because drains in the streets get plugged from all the leaves falling," Smith said. "It's a big enough storm that you want people to bring things in. Clean out your gutters and take precautions like that."
A flash flood watch for recent burn areas in Southern California is in effect starting Thursday through early Friday morning.
"Part of the thing that can increase the risk of flash flooding is not just the amount of rain but the rain rates. It's not unusual, but these burn areas... are really subject to turning into debris flows with heavy rain rates," Smith said.
Residents near the burn areas of the San Gabriel Complex, Sand and Colby fires should take extra precautions, Lee said.
The natural erosion of hillsides that comes with rain is exacerbated when there's no vegetation to hold the soil back, Lee told KPCC. That means rocks, tree limbs and other debris can come washing down the mountain in a powerful stream.
The county has already prepared special debris basins, which are designed to capture and redirect the flow of mud and water. But residents still need to take precautions, Lee said.
"Our debris basins and channel systems are very effective and have proven very effective over the past decades in protecting communities, but Mother Nature is pretty incredible," he said.
A car parked in front of the basin or trash and recycling bins blocking the flow could lead to increased flooding.
Lee also advised residents to pick up pet waste and remove any fertilizer or pesticides, because these things can wash downstream and pollute the environment.
Given the capacity of the county's debris basins to handle severe storms, Lee said he was "cautiously optimistic" heading into this one.
Winds are expected to reach about 30 miles per hour on Friday, with gusts of up to 40 miles per hour, she added. She recommends that motorists driving through the Grapevine exercise precaution.
Temperature highs on Friday will be around 50 to 60 degrees in the mountains. For the L.A. basin area, highs will top about 60 to 63 degrees.
This story has been updated.