Steady rain doused the Southland Thursday amid strong winds and mandatory evacuation orders in parts of Orange and Riverside counties prompted by fears of shallow mudslides, minor debris flows and some flash-flooding over areas of L.A., Orange, Ventura and Riverside counties recently denuded by wildfires.

While light rain was reported in much of the Southland early Thursday, the National Weather Service reported shortly after 3 a.m. that heavy rain was falling in Burbank and Downtown L.A.

According to an National Weather Service statement, the heaviest rain is expected in Orange County and inland areas late Thursday morning.

“Hourly rainfall rates in stronger showers and isolated thunderstorms could approach one-half to one inch in an hour,” according to the NWS. “This could lead to mudslides and debris flows at recent burn scars. The time window of greatest concern is from late Thursday morning through early Thursday evening.”

Shortly before 7:30 a.m., the NWS issued a flood advisory for east central Ventura County and west central L.A. County in response to Doppler radar indications that minor flooding was impending. The NWS said in a statement that locations that would experience flooding include Thousand Oaks, Simi Valley, Malibu, Agoura Hills, Woodland Hills, Calabasas, Westlake Village, Malibu Creek State Park and Oak Park. The advisory will expire at 9:15 a.m.

The NWS said moderate to heavy rain has been falling on L-A. County.

“Reports of rocks on canyon and mountain roads have been reported, as well as flooded freeway lanes and offramps,” a statement said. It said this could persist until 11 a.m.

The NWS said a flood advisory would remain in effect in L.A. County until 10:45 a.m. and that locations that would experience flooding include Long Beach, Acton, Wrightwood, Glendora, Alhambra, West Covina, Mount Wilson, and Whittier.

The NWS also issued an urban and small stream flood advisory that will be in effect until 11:45 a.m. in Orange, Riverside and San Bernardino counties. It said locations that that will likely experience urban and low lying flooding include Anaheim, Santa Ana, Riverside, Irvine, San Bernardino, Fontana, Moreno Valley, Huntington Beach, Garden Grove and Ontario.

“Turn around, don’t drown when encountering flooded roads. Most flood deaths occur in vehicles,” an NWS statement urged motorists.

In Orange County, the sheriff’s department Wednesday issued a voluntary evacuation order for homes within Trabuco Canyon, Rose Canyon and the Mystic Oaks and El Cariso areas. Those orders could be upgraded to mandatory if debris flows are spotted, or if bridges or roads become impassible due to flooding, said Carrie Braun, a spokeswoman for the Orange County Sheriff’s Department.

Orange County officials plan to set up an incident command post near City Hall in Rancho Santa Margarita Thursday morning, Braun said.

Most areas should see between a half-inch and two inches of rain, although three inches could fall at higher elevations and foothills.

A flash flood watch will be in effect for the Santa Ana mountains and foothills and inland Orange County throughout the day Thursday and into early Friday morning.

The storm originating in the Gulf of Alaska began moving across California’s Central Coast Wednesday afternoon and into Ventura County, reaching Los Angeles County in the evening strengthened by moisture from the Eastern Pacific. Forecasters expected the Thursday morning commute to pose challenges.

The storm was generating strong, gusty winds, prompting the NWS to issue a wind advisory on Santa Catalina Island; the San Gabriel and Santa Monica mountains; the Antelope, San Fernando, Santa Clarita, Pomona and San Gabriel valleys; L.A. County Beach cities, metropolitan Los Angeles, including Downtown L.A., and the Hollywood Hills.

In the mountains and the Antelope Valley, the wind was forecast to blow at 20-30 miles per hour, with 50-mph gusts. In the other L.A County areas subject to a wind advisory, winds of 15-30 mph with 40-mph gusts were expected. The advisory, indicating winds or gusts of at least 35 mph, was scheduled to be in effect until midnight.

“Gusty winds will make driving difficult, especially for high profile vehicles,” warned the NWS in a statement.

Showers are expected By Thursday afternoon.

Forecasters say the rain will fall on the sites of the Woolsey Fire in L.A. and Ventura County, the Hill Fire in Ventura County and the Thomas Fire that burned in Ventura and Santa Barbara counties in December 2017.

Ahead of the storm, residents made preparations in Malibu, much of which was devastated by the Woolsey Fire this month. In Orange and Riverside counties, residents near the Holy Fire burn area were being urged to evacuate before the rain began falling. Mandatory evacuation orders were issued late Wednesday afternoon for some areas of Lake Elsinore in Riverside County.

“All Malibu residents are urged to prepare for potential flooding, mudslides, power outages and evacuations,” the city said in a statement Tuesday. But those preparations must not involve removing debris, which contains hazardous materials. No debris removal from burned properties is allowed until inspections by state and county health officials have been completed.

The Los Angeles County fire and sheriff’s departments both deployed additional staffing into the burn area in light of the threat of potentially damaging flooding. Officials with both agencies stressed the need for residents to adhere to whatever evacuation orders are issued.

“Evacuation orders should not be taken lightly and are ordered because there is a threat to life and property,” according to a joint statement from the agencies.

Along the coast, a high surf advisory was scheduled to be in force until 10 a.m., when it will be replaced by a high surf warning scheduled to be in force until 10 a.m. Friday. The NWS said surf of 10 to 18 feet with sets of up to 20 feet would batter the shore, and a second, larger swell would generate surf of 20-24 feet later Thursday morning through Friday morning. The surf will lower to 10-15 feet Friday afternoon and evening.

In Orange County, where surf of 5-10 feet was pounding the shore Thursday morning, a high surf advisory will be in effect until 10 p.m. Friday, after which the surf will gradually subside, forecasters said.

The NWS forecast L.A. County highs Thursday of 51 degrees on Mount Wilson; 57 in Palmdale; 58 in Lancaster; 60 in Saugus; 62 in Pasadena and Woodland Hills; 63 in Downtown L.A., San Gabriel and at LAX; and 64 in Long Beach and Avalon.

For Orange County, the NWS forecast highs of 46 on Santiago Peak; 55 on Ortega Highway at 2,600 feet; 59 in Fremont and Trabuco canyons; 62 in Yorba Linda; 63 in Laguna Beach and Mission Viejo; 64 in San Clemente and Anaheim; and 65 in Fullerton, Newport Beach and Irvine. In contrast with the norm, there was little difference in temperature Thursday between coastal and inland communities, which are usually several degrees higher.

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