Southern California goes on flood watch

Storm includes strong wind gusts, downpours, possible mud and debris flows in the forecast

A winter storm anticipated to arrive in LosAngeles County overnight Sunday could bring flooding, mud and debris flows and strong wind gusts throughout Southern California until midway through the week, forecasters said.

A flood watch has been issued for most of the region through Tuesday night, and a winter weather advisory was issued for higher elevations. High surf is anticipated along the coast.

Parts of Los Angeles County, including Pasadena and the San Fernando Valley, could see nearly 3 inches of rain from Sunday night through Wednesday, according to projections from the National Weather Service. Others in the southern portion of the county could see less than 2 inches.

The storm system could start in Los Angeles County with light rain as early as Sunday night, NWS meteorologist David Gomberg said Sunday afternoon. More moderate to heavy rainfall, including pockets of significant bursts, should begin this morning.

“Because of that rainfall last week … it’s not going to take much rain to cause significant problems over the next few days,” Gomberg said.

“Over the past week, the City has worked to repair more than 4,000 potholes, reinforce hills that are at risk of mudslides and prevent power outages by making repairs to underground equipment and vaults that had flooded during the previous storm,” Mayor Karen Bass said Sunday on X.

The heaviest rainfall was anticipated in Los Angeles County tonight and Tuesday night, with peak rainfall rates between 1/2 inch and 1 inch per hour, Gomberg said. Moderate rain was anticipated to start Sunday night.

“It’s a more convective system with this and what that means, basically, is you could get some high-intensity rainfall rates,” Gomberg said. “Think of it as higher intensity, shorter duration rainfall.”

L.A. County Public Works officials issued a “debris flow forecast,” saying moderate flooding and mudflow/sediment deposition should be anticipated in the area of McDonald Creek, Del Arroyo Drive and La Tuna Canyon Road, according to the L.A. Fire Department.

“If conditions worsen, evacuation orders may be issued and evacuation sites will be identified,” the LAFD said. “Take action now to be ready to quickly evacuate if you live on the streets along La Tuna Canyon Road with the borders of Horse Haven Street to the north, Martindale Avenue

to the east, Penrose Street to the south, and Ledge Avenue to the west.”

There is a 10% to 20% chance of isolated thunderstorms Sunday night through Tuesday, forecasters said.

The storm would then move into Orange County and the Inland Empire, though it looked like the system had been “slowing down a bit,” NWS meteorologist Elizabeth Adams said.

Most areas in Orange County were projected to receive 11/2 to 2 inches through Wednesday, while areas of the Inland Empire were projected to see less, Adams said.

“The ground is pretty saturated from the last few weeks so there will be concerns due to runoff that could result in flooding, especially in low-lying areas,” Adams said.

Orange County could begin seeing light rain today, but Adams said the heaviest rainfall was projected for Tuesday with lingering rain chances likely through Wednesday morning. There is a high chance of thunderstorms in the area.

Snow accumulations could get as low as 5,500 feet in Los Angeles County mountain ranges and as low as 6,000 feet in Orange County and the Inland Empire, forecasters said. Most of the snow accumulations would remain above 7,000 feet.

A high surf advisory was in effect for the Orange County coast from 4 p.m. Saturday to 10 p.m. Tuesday. A winter weather advisory was scheduled to be in effect for the San Bernardino and Riverside county mountains from Tuesday morning to Wednesday morning.

A coastal flood advisory would be in effect for L.A. County beaches from Sunday morning to 9 a.m. Tuesday morning, according to NWS.

Peak wind gusts could reach 40 mph in L.A. County valley areas and up to 60 mph in the foothills and mountains, Gomberg said, adding that with the saturated soils, there was the possibility for downed trees.

Strong winds were not expected in Orange County or the Inland Empire today, but breezy conditions this afternoon into Tuesday could make the region feel colder. Coastal areas of Orange County could see gusts of up to 30 mph Tuesday evening, NWS meteorologist Casey Oswant said.

The storm’s impacts would likely be greater in areas northwest of L.A. County, including San Luis Obispo, Santa Barbara and Ventura counties, Gomberg said.

“It’s not looking like it’s going to be quite as heavy as the past few storms,” Adams said, “but people should stay vigilant and updated.”