Light rain fell over much of Southern California early Friday, marking the start of what is expected to be a significant dousing of rain that forecasters say could trigger flooding and mudslides, particularly in recent burn areas, where evacuation warnings were in effect.
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Most Southern California residents awoke to wet conditions Friday as the first of two bands of rain made its way into the region, leading to slick roads during the morning commute. The rain was expected to intensify in the Los Angeles area late Friday morning before tapering off in the afternoon.
The much stronger second band of rain was expected to arrive Friday night and linger through much of Saturday.
"During this time, folks should be prepared for ample traffic incidents, delays, and a few road closures," according to the National Weather Service. "This includes a few flooded roads, freeway lanes, and onramps and offramps. Canyon roads, especially the most vulnerable ones like Topanga Canyon, will likely see mudslide and rockslides. In and near recent burn scars, at least shallow debris flows will occur which would impact roads, with a moderate risk of significant flows blocking or damaging roads and impacting structures. This includes the Palisades, Eaton, and Bridge burn areas which have the highest threat.
"In creeks and rivers, the flows will be heavy with anyone in or near those channels at risk of being swept away. There will be an area of heaviest rain, but we do not know for sure exactly where that will be."
Forecasters said most of the area will receive between 3 and 6 inches of rain before the dual systems move out of the region Sunday.
Aside from the sheer amount of rain, the bigger concern in flood-prone areas is the rainfall rate -- with flooding and debris flows generally triggered by heavy downpours that drop a large amount of precipitation in a short period of time.
The NWS predicted that during the peak of the storm Friday night into Saturday, many areas could see rainfall rates of a half-inch to an inch per hour, while others will see lower rates of a quarter- to half-inch per hour.
"When considering the rain we have already seen and will continue to see (Friday), which should precondition the ground and lower the bar of what sort of additional heavy rain is needed to trigger flash flooding, the risk for significant and potentially damaging flooding continues to be moderate to high with the expected rain rates."
A flood watch issued by the NWS will be in effect from late Friday night through Saturday evening for the entirety of Los Angeles County, along with most of Santa Barbara and Ventura counties.
The city of Los Angeles issued an evacuation warning that'll be in effect through 11 a.m. Sunday for residents near the Palisades, Hurst and Sunset fire burn zones. Mayor Karen Bass said evacuation orders will be in effect from 8 p.m. Friday through 8 a.m. Sunday for "select vulnerable properties within burn scar areas." It was unclear how many properties were being placed under the evacuation order, but police were expected to visit each affected home and notify residents.
County officials issued an evacuation warning for residents near the Eaton Fire area in Altadena. County officials warned that any other recent burn areas could also be at increased risk of flooding or debris flows.
The city of Los Angeles' Emergency Operations Center was activated Thursday night, and the mayor's office was coordinating with the Emergency Management Department, Los Angeles Fire Department, Los Angeles Police Department, Los Angeles County Public Works and relevant city departments to ensure all personnel are ready to respond as needed to keep residents safe, officials said.
The county was offering residents free sandbags for pickup at the Public Works Fleet Maintenance Yard, 252 Mountain View St. in Altadena, and at the Malibu Library parking lot, 23519 W. Civic Center Way. The LAFD was providing free sandbags at fire stations throughout the city, with sand available at some of those locations. A listing of locations and more information is available at https://lafd.org/news/lafd-provides-sandbags- homeowners-1.
Gov. Gavin Newsom said the state pre-deployed emergency response crews in Los Angeles, Orange and Ventura counties to enable faster response to any storm-related issues that develop. He said 274 personnel were being deployed, along with 18 engines, three Urban Search & Rescue companies, six bulldozers, three swiftwater-rescue teams, three helicopters and five dispatchers.
In the Palisades Fire area, Caltrans closed Topanga Canyon Boulevard between Pacific Coast Highway and Grand View Drive at 10 p.m. Thursday. Caltrans officials said motorists should expect the stretch to remain closed at least through the Friday morning commute, but potentially through the weekend, depending how the storm develops.
That stretch of Topanga Canyon has been undergoing nightly repairs, with the road closed between midnight and 5 a.m.
NWS forecasters urged homeowners to prepare for the rain by ensuring gutters are cleared and windshield wipers are secure and working. They said people should consider rescheduling outdoor events, and advised motorists to avoid driving through flooded areas.
"Avoid the roads, stay indoors as much as possible, and stay aware of your environment," forecasters said. "If you have to drive, allow extra time as traffic will be increased due to slippery roads, low visibility, and localized flooding. If you are near a burn scar, heed the advice of local officials as they know your area best. Reschedule and avoid outdoor activities. If you are outside and hear thunder, see lightning, experience sudden wind shifts, or a sudden increase in rain intensity, head indoors immediately and stay away from windows. Stay out of, and far away from, any streams, rivers, and canyons -- especially campers. Avoid parking near tall trees. Be ready for sudden power outages. Boaters, please stay in safe harbor. For everyone, stay tuned to your local news outlet and weather.gov for any updates."
The Los Angeles County Sheriff's Department issued a statement Wednesday urging people to be prepared, offering a series of tips:
-- Drive carefully, slow down and allow extra stopping distance;
-- avoid flooded roads, turn around, wait it out;
-- prepare your property by gathering sand bags, and checking gutters and drains; and
-- check the condition of your vehicle and replace windshield wipers and tires if needed.
Sheriff's officials urged people to use websites like http://Ready.Lacounty.gov to stay up to date on road closures, weather alerts, and emergency notifications.
"Our deputies will be out monitoring conditions and ensuring community safety," according to the department. "Let's all do our part to stay safe during the storm."
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