Rain keeps soaking Southland, to persist until Friday

A strong storm system continued pushing through the Southland Thursday, with forecasters saying the area can expect periods of “moderate-to-heavy” rain that will linger into Friday.

The brunt of the storm was unleashed primarily in Ventura County overnight, where thunderstorms and even a possible tornado pounded the region, dropping rain at rates topping 3 inches per hour.

Los Angeles County saw some pockets of heavy rain, with more of the same anticipated Thursday.

“The areas of mid-level instability will continue and (thunderstorm) development is possible through the day and into the evening,” according to the National Weather Service. “All of these areas will likely see periods of dry conditions and periods of wet to very wet conditions today (Thursday) and this evening. Rainfall rates for the most part will be around 0.3 to 0.6 inches per hour but there is a possibility for double those rates under heavier cloud bursts. One to 3 inches of additional rain is likely (Thursday) but there could be more under areas with (thunderstorms) or under training cells. A few areas may even see less than that.”

Showers will likely persist in Los Angeles County Thursday night and Friday morning, with some lingering rain possible into Saturday morning in eastern portions of the county, forecasters said.

Dry conditions should prevail by Saturday, continuing through the holiday weekend.

A flood watch will remain in effect for the bulk of Los Angeles County until late Thursday night. In Orange County, a flood watch will be in effect Thursday evening through Friday evening.

Los Angeles County Public Works officials heightened the agency’s mudflow warning level for recent burn areas, alerting residents that debris flows are possible. The heightened alert affects recent burn areas in the Topanga Canyon, Agua Dulce, La Tuna Canyon and Duarte areas.

Duarte city officials announced that the Fish Fire burn area will move to a “yellow alert” status at 4 p.m., continuing until 8 a.m. Friday. The alert affects roughly 25 homes along Mel Canyon Road between Brookridge and Fish Canyon roads. Parking restrictions will be in place along that stretch, as well as on Deerlane Drive between Mel Canyon Road and Greenbank Avenue.

Residents in the affected Duarte area were also instructed to remove all trash bins from the street, and place them on their driveways closer to their homes, where they will be picked up manually at the 25 homes in the alert area. On Friday morning, student dropoffs at Valley View Elementary School will take place on Deerlane Drive. No dropoffs will be permitted on Mel Canyon Road, officials said.

In the Topanga Canyon area, an evacuation warning was issued for roughly 20 homes along Santa Maria Road north of Topanga Canyon Boulevard.

Six Flags Magic Mountain theme park in Valencia was closed for a second straight day due to the storm. Park officials said tickets purchased for those days can be redeemed any other day for the rest of the year.

Los Angeles County Lifeguards warned people to exercise caution if they visit the beach.

“Ocean conditions will also have a bit more activity with waves in the head to overhead range,” lifeguards warned on social media. “Plenty of varying factors these next few days, so make sure to stay tuned, and if you decide to come to the beach make it a point to check in with a lifeguard tower prior to entering the water.”

County health officials issued their standard warning for people to avoid entering the ocean water in the days following rain, noting that runoff can carry bacteria and debris into the ocean, raising the risk of illness.

Snow levels are expected to remain above 7,500 feet, with several inches possible at elevations over 8,000 feet.

Los Angeles County officials said various agencies were coordinating to ensure public safety while also hoping to capture as much stormwater as possible for future use.

“L.A. County owns a world class system of water conservation and flood protection. This system is prepared to capture and conserve valuable stormwater while protecting communities,” county Public Works Director Mark Pestrella said in a statement earlier this week. “Our system is primed to capture as much stormwater as possible in our efforts to increase the region’s overall local water supply by 600,000-acre feet by 2045.”

County officials urged residents to heed instructions from emergency responders and alert notifications; drive cautiously and slow down in storm conditions; and avoid trying to cross flooded roadways.

Daytime temperatures will remain in the 60s in the region for much of the week. Overnight lows will generally be in the upper 40s and lower 50s throughout the Southland, but will dip into the 30s in some parts of the mountains and high desert.

Inland Empire

Rainstorms this week throughout the Inland Empire have and will produce occasionally heavy downpours, prompting the National Weather Service to issue a flood watch that will be in effect until Friday and a winter weather advisory that will be in effect from Thursday until Saturday.

“Moisture will be abundant through this week,” the NWS said in a statement. “The beginning of the heavier rain will … likely begin late Wednesday night and early Thursday in Riverside and San Diego counties. Most of the heavier precipitation will be convective due to the instability of the low pressure. Hourly rainfall rates of 1 inch appear in some of the (models) for Thursday night.”

The flood watch runs until 4 p.m. Friday while the winter weather advisory runs from 6 p.m. Thursday to 4 a.m. Saturday.

Wet snow is expected above 6,500 feet with total snow accumulations of 1 to 3 inches at elevations from 6,500 to 7,500 feet, 3 to 6 inches from 7,500 to 8,000 feet and 6 to 12 inches above 8,000 feet in the Riverside County Mountains.

As of 5 a.m., there was 0.48 inches of rain reported in Norco and 0.47 inches reported at Prado Dam. There was 0.28 inches of rain reported in Temecula and 0.26 inches reported at March Air Force Base.

Forecasters said two troughs of low pressure will slide through California, with the current one exiting to the east Wednesday, and the next one reaching the coast as an occluded front soon afterward, moving slowly across the region, gradually pushing into Arizona by Saturday.

The NWS predicted isolated thunderstorms, with the highest probability on Thursday.

“Snow levels will generally be above 7,000 feet through Friday but start to drop after that as moisture decreases, possibly to 6,000 feet Saturday,” the NWS stated. “The highest roads and ski resorts will encounter accumulating snowfall, with Big Bear mostly receiving rain. Winds generally will not be an issue with this storm, but some gusts over 30 mph could occur in the mountains and deserts around Thursday.”

The official start of winter is Thursday.

Temperatures will remain average throughout the storm series, with no influence from the Polar jet stream, according to meteorologists.

In the Riverside metropolitan area, highs will be in the mid-60s thorough Friday, with overnight temperatures in the low 50s.

In the Coachella Valley, the daytime mercury will hover around 70 and fall into the mid-50s overnight this week, while in the Temecula Valley, the temperature band will be virtually identical to Riverside metro, though the daytime high will peak in the upper 50s on Friday.

Updated Dec. 21, 2023, 1:21 p.m.

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