Rains hit SoCal for much of this week. Why it’s probably not a fire killer
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Back-to-back atmospheric river storms began to hit Los Angeles County Tuesday night — giving the region much-needed moisture ahead of another potential round of Santa Ana winds.
Forecasters were optimistic that the rain would, primarily, be beneficial for Southern California, reinvigorating vegetation left vulnerable by a historically dry start to the water year without unleashing devastating mudslides in recently burned areas.
Meanwhile, the storms hit Northern California harder than anticipated, with landslides and urban and stream flooding reported.
In L.A. and Ventura counties, the National Weather Service has estimated there’s a 5% to 10% chance of significant debris flow in fire-scorched parts of the Southland. That still can change, however, especially if the second storm strengthens or changes its path of approach later this week.
Still, officials were preparing for possible danger near L.A. County burn scars.
The California Department of Transportation closed a stretch of Pacific Coast Highway, from Chautauqua Boulevard in Los Angeles to Carbon Beach Terrace in Malibu, beginning Tuesday afternoon because of the risk of debris flows. Topanga Canyon Boulevard between PCH and Grand View Drive also is closed.
The scenic highway had fully reopened Monday morning after a weeks-long closure during the Palisades fire.
“Out of an abundance of caution, the highway must be closed due to soft soils on both the hill and ocean sides of the road. Mud and debris flows may occur and canyons may overtop, blocking the road or causing further damage,” Caltrans wrote in a news release.
As more moderate and heavy rain moved in Tuesday night, the National Weather Service issued a flood advisory for western San Luis Obispo County, warning of minor flooding in low-lying areas. The affected area includes the city of San Luis Obispo, as well as Paso Robles, Cambria, Morro Bay and Pismo Beach.
The first in the series of atmospheric rivers arrived Friday in Northern California.
The second atmospheric river arrived late Monday.
By Tuesday morning, there were several reports of landslides across the North Bay, with urban and stream flooding. In San Francisco, a pothole measuring about 5 feet by 4 feet opened up in the Marina District amid heavy rain. A KGO-TV news crew reported that multiple autonomous Waymo cars drove through the pothole at full speed, ignoring efforts by crews to get the vehicles to avoid the hazard.
Several downed trees, including one that fell on a person and another that took down power lines, were also reported in the city. A massive tree fell at Steele Lane Elementary School before noon Monday in Santa Rosa, damaging a building and forcing a nearby road to close. No one was injured.
In Forestville, a rain-saturated hillside gave way near the Hacienda Bridge, sending a home sliding into the Russian River in the afternoon. No one was inside the house at the time, according to the Sonoma County Sheriff’s Office.
A flood watch was in effect for a wide swath of Northern California on Tuesday and was expected to last through early Wednesday, according to the weather service.
Flooding also closed several roads in Marin County, including California 1 between Point Reyes Station and Bear Valley Road. In Sonoma County, most lanes of the 101 Freeway in Windsor were shut temporarily due to heavy flooding.
In the afternoon, a severe thunderstorm warning was issued for San Francisco and swaths of San Mateo and Marin counties, bringing warnings of gusts of up to 70 mph and the potential for considerable damage to trees, roofs and mobile homes.
The Russian River in Guerneville was forecast to reach minor-flood stage early Wednesday. An evacuation order was issued for low-lying areas of the Russian River, a stretch of about 32 miles, from unincorporated Healdsburg all the way downstream to the Pacific Ocean.
Concerns over flooding prompted officials to close schools in the community Tuesday.
Evacuations were ordered at a medical facility in Santa Rosa and a neighboring Hampton Inn after parking lots flooded, partially submerging some cars, the Press Democrat reported.
Mud from a hillside flowed into an apartment building in the town of Fairfax in Marin County, according to KPIX-TV. No injuries were reported.
The atmospheric river is expected to unleash on Southern California beginning Tuesday night, according to the weather service.
The wet weather comes after a disastrous start to 2025 for Los Angeles County, with the Eaton fire scorching more than 14,000 acres in the Altadena area and the Palisades fire burning 23,400 acres on the Westside of Los Angeles. More than 16,000 structures, including many homes, were destroyed in the firestorms.
A report from UCLA’s Anderson Forecast released Tuesday estimated the total property and capital losses from the wildfires could range from $95 billion to $164 billion. The report warns that, without significant investment in wildfire mitigation strategies, “Californians will face increasingly higher insurance premiums and growing health risks from wildfire-related pollution” in coming years.
Forecasters are hopeful that this week’s storms might bring enough moisture to significantly reduce the fire risk across Southern California. But it won’t be enough to wipe out the risk, the weather service said.
“While the rains will have provided temporary relief with high moisture in some fuel types, the expected rain this week will not be enough to completely end high fire season,” said Kristan Lund, a meteorologist with the National Weather Service in Oxnard.
A primary reason is simply how dry vegetation is across the southern part of the state.
It typically takes three to six weeks for vegetation such as chaparral and coastal sage to soak up moisture from rainfall.
A stronger atmospheric river is set to hit Northern California on Monday and then hit L.A. County on Tuesday, aiding hopes of helping end a devastating fire season.
Even so, last month’s storm has made a difference. Data indicate that vegetation has absorbed plenty of moisture, said Alex Tardy, a meteorologist with the weather service’s San Diego office.
“As long as it stays cool, and we don’t have additional Santa Ana winds and get a little bit of precipitation like we’re going to see this week — that buys us time in February,” Tardy said. “A little bit of rain and snow goes a long way in the middle of the winter.”
Downtown Los Angeles received 0.54 of an inch of rain Jan. 25 through Jan. 27, and it’s possible that downtown could get an additional four-fifths of an inch of rain through Friday.
Lawmakers are calling on the state to expedite rules for ember-resistant defensible space zones around homes that some experts say may have helped mitigate the damage from Los Angeles’ devastating wildfires.
Even if that happens, that total would still be short of the widespread 2 to 4 inches of rain meteorologists say are necessary to comfortably and definitively call an end to the fire season.
Should a particularly dry Santa Ana wind develop later this month, the situation could change dramatically.
“If we got a really dry Santa Ana next week, instead of a rainstorm, we could still have potential for extreme fire behavior,” Lund said. “Any time we have that combination of dry air and strong winds — and it could just be no more rain for like a week or two — could even put us back into that risk for high fire [weather danger].”
Another Santa Ana wind event could come by the weekend
Winds are expected to pick up Friday through Monday, with the strongest gusts anticipated Saturday, according to the weather service.
Santa Ana winds bring in dry gusts, flowing from the high desert over mountains and through canyons, drying out vegetation as the cold air descends from an area of high pressure and compresses and warms up as it seeks areas of lower pressure by the coast.
Santa Ana winds are capable of increasing fire risk — especially if combined with dry vegetation.
Despite the recent rain, much of Southern California is still dry, having received less than 25% of the typical rainfall for this point in the season, with some areas getting even less than 10%. The Santa Ana wind season can last through March.
Forecasters don’t anticipate significant fire risk this weekend from the incoming round of Santa Ana winds, given the rain.
Toxic chemicals from L.A.’s fires are going underreported and pose serious long-term risks, a group of lawmakers says. They want the EPA to create a task force.
Still far behind on rainfall this season
Many communities are still running well behind their typical annual rainfall. The droplet deficit is 5 to 8 inches across a swath of Southern California, Tardy said.
Downtown L.A. has received just seven-tenths of an inch of rain since the water year began Oct. 1 — just 9% of its typical average by this time of year.
San Diego has received just 0.35 of an inch, a record low start to the water year since regional recordkeeping began in 1850. It’s also just 7% of San Diego’s average for this point of the season.
The rain deficit for San Diego is about 5 inches: “That’s half of our annual rainfall that is missing,” Tardy said. And downtown Los Angeles’ deficit is nearly 7 inches — also nearly half of its average yearly rainfall.
The big question is what February — traditionally “our wettest month in California” — will bring, Tardy said.
The Trump administration abruptly sent water flowing from two California dams. The action could leave less water in dams for the summer, when farmers typically use it.
Possible dry weeks ahead
There’s a possibility that dry conditions will return later this month.
“Overall, we keep cold air,” Tardy said. “So, cold air really just becomes dominant across the northern United States really, from the Pacific Northwest all the way to New England.”
As a result, the jet stream — the fast current of air that moves from west to east — won’t be over Southern California. To get more rain, Southern California would like to be under the jet stream and have a chance to grab the moisture it ferries, Tardy said.
The latest forecast models suggest that the jet stream will instead go over Washington and Oregon, then descend to the southeast over Nevada and Arizona.
“That means we get on the dry side, which could even give us a little bit of offshore Santa Ana wind,” Tardy said. “It certainly doesn’t give us much of a chance for getting precipitation, but it does keep the temperatures cool and cooler than average for the second week of February.”
In other words, it’s “not looking promising for precipitation down here,” he said.
There is, however, a potential storm system developing in the Pacific Ocean, which could arrive by mid-February, Tardy said. Still, that’s “not much opportunity for precipitation of any significance coming up.”
California’s snowpack stands at 65% of average for this time of year. After a dry January, major storms are forecast to bring more rain and snow.
This week’s forecast
The first of two atmospheric river storms was expected to peak in Los Angeles and Ventura counties Tuesday night and last through midday Wednesday, with the second storm expected to start Thursday night into Friday morning.
“We’re most likely just seeing light-to-moderate rain amounts and rain rates with minor impacts,” said Todd Hall, a meteorologist with the weather service’s Oxnard office.
Both storms are of the “Pineapple Express” variety, so named because they carry tropical moisture from the ocean near Hawaii to the mainland.
During the first storm, peak rainfall rates could be light — from one-tenth of an inch per hour to one-quarter of an inch per hour. In Ventura, Santa Barbara and San Luis Obispo counties, peak rain rates could be moderate — a quarter of an inch per hour to half an inch per hour, although there could be isolated locations with up to three-quarters of an inch per hour.
The key threshold for rainfall rates that can trigger significant debris flow is half an inch per hour or greater, meteorologists say.
More rain could finally end Southern California’s fire season as Pacific Coast Highway is open for the first time in weeks.
There is a 10% to 20% chance that rainfall rates could get up to two-thirds of an inch per hour over the burn area of the 2024 Lake fire, which scorched 38,664 acres in the Santa Barbara County mountains north of Los Olivos.
There is a moderate chance — 30% to 40% — of rainfall rates of about three-fifths of an inch per hour to three-quarters of an inch per hour across San Luis Obispo County.
Rainfall has the potential to be particularly focused on south-facing mountain slopes and hillsides, because of the path of the moisture arriving in the region, Hall said.
In L.A. County, the biggest rain-related effects are likely to be minor creek and roadway flooding.
A deep analysis of the Palisades fire evacuation paints a chaotic scenario: As the fire roared toward homes, major escape routes were gridlocked before the first evacuation orders were given.
The most likely scenario for L.A. County’s first storm is peak rainfall arriving from 10 p.m. Tuesday through midday Wednesday. Long Beach and Covina could get a quarter of an inch of rain; Santa Clarita, about a third of an inch; and downtown L.A., Redondo Beach and Canoga Park, about two-fifths of an inch.
Rainfall totals probably will be higher to the north and west. In Ventura County, Thousand Oaks could get half an inch of rain; Fillmore, three-quarters of an inch; Oxnard, four-fifths of an inch; and Ojai, 1.64 inches. Santa Barbara could get 1.19 inches; San Luis Obispo, 1.47 inches; and Cambria, 1.96 inches.
For the second storm, the most likely scenario is peak rainfall occurring Thursday night and early Friday. Long Beach, Redondo Beach, Santa Clarita, and Thousand Oaks could get about a third of an inch of rain; downtown L.A., Oxnard and Canoga Park, two-fifths of an inch; Covina, half an inch; and Santa Barbara, three-fifths of an inch.
Snow levels in L.A. County will remain above 6,500 feet to 8,000 feet above sea level.
In the Sierra, officials issued a backcountry avalanche warning for the Lake Tahoe area Tuesday because of heavy snow, rain falling on snow and strong winds. The warning is expected to last through Wednesday.
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