Lead
An atmospheric river moving into Southern California this week prompted evacuation warnings across parts of Los Angeles County beginning Thursday evening, as forecasters warned of both destructive mudflows and a chance to materially reduce fire risk. The National Weather Service’s central scenario has downtown Los Angeles receiving about 2.62 inches of rain from Friday morning through Sunday, though forecasts range from around 1.39 inches to as much as 4.81 inches. Officials placed areas near recent burn scars under evacuation warnings from 6 p.m. Thursday through 11 a.m. Sunday because heavy rain could mobilize debris and mud. At the same time, meteorologists say widespread totals of 3 to 4 inches at low elevations would significantly blunt this year’s high fire season.
Key Takeaways
- Evacuation warnings were set to begin at 6 p.m. Thursday and run through 11 a.m. Sunday for communities near recent burn scars in Los Angeles County.
- The National Weather Service’s most likely forecast: downtown Los Angeles about 2.62 inches of rain Friday–Sunday; lower-end scenario ~1.39 inches (≈25% chance); higher-end ~4.81 inches (≈25% chance).
- Meteorologists say 3–4 inches of widespread rain in low elevations is typically needed to end high fire season in Southern California.
- Already this season downtown L.A. has recorded 1.41 inches of rain; last year it had 0.07 inches Oct–mid-Nov and only 0.16 inches by Jan. 7, 2024—conditions that preceded deadly January 2024 fires.
- Peak hourly rainfall rates are forecast between 0.25 and 0.5 in/hr, with bursts possible up to 1 in/hr; debris flows can be triggered at about 0.5 in/hr in steep burned terrain.
- There is a 10–30% chance of thunderstorms across the region Friday–Saturday, with a small chance of localized damaging winds or a brief tornado.
- Topanga Canyon Boulevard was scheduled to close at 10 p.m. Thursday between Pacific Coast Highway and Grand View Drive due to debris-flow risk.
Background
Southern California faces a recurring late‑autumn crossroads between Santa Ana wind events that fan wildfires and the arrival of Pacific storm systems that bring rain. In January 2024, record dry conditions and erratic Santa Anas helped rapidly spread the Eaton and Palisades fires, producing some of the state’s deadliest and most destructive blazes. That season’s prolonged dryness left grasses and shrubs exceptionally receptive to ignition, elevating the stakes for any strong winds before meaningful rainfall arrived.
Climate factors and human development have compounded the risk. Warmer temperatures linked to climate change lengthen drying periods for vegetation, while expanding homes and infrastructure in wildland‑urban interfaces raise exposure. Natural climate variability adds further complexity: La Niña patterns often correlate with drier winters in California, yet historical records show large floods and heavy rainfall have occurred during some La Niña years as well, meaning seasonal outlooks remain probabilistic rather than deterministic.
Main Event
The incoming system is an atmospheric river that meteorologists say will affect different parts of the region at different times, with two expected peaks for the Los Angeles area: late Thursday night into early Friday, and again Saturday. Forecasters for Ventura County anticipated the highest certainty of rain from Thursday night through Saturday night, while Los Angeles County’s window is Friday morning through Saturday night. San Diego, Orange County and the Inland Empire are forecast to see moderate rain Friday with the heaviest potential Saturday.
Forecasters described significant uncertainty about the system’s eventual track and intensity because it is associated with a cut‑off low—an isolated low‑pressure vortex decoupled from the main jet stream. If the low stalls offshore and draws prolonged, moist southeast flow, that could produce sustained heavy rainfall and bursts that trigger flash flooding and debris flows. Conversely, if the low spins away from the coast the region could receive substantially less precipitation.
Rainfall projections for through Sunday include 2.38 inches for Long Beach, 2.48 for Redondo Beach, 2.49 for Oxnard, 2.63 for Thousand Oaks, 2.77 for Santa Clarita, 2.89 for Covina and 3.59 for Santa Barbara. San Diego was forecast at 1.5–2 inches, Riverside/San Bernardino/Escondido 2–2.5 inches, San Clemente 2.5–3 inches, and Anaheim/Irvine 3–4 inches. Mountain and desert totals vary: Palm Springs could see 1–1.5 inches, Joshua Tree 1.5–2 inches, with higher elevations in the Sierra expecting snow on passes.
Analysis & Implications
If the storm delivers higher‑end rainfall totals across low elevations, the immediate public‑safety effect would be twofold: a meaningful reduction in near‑term wildfire risk coupled with elevated hazards from flooding and debris flows, particularly in recently burned watersheds. A seasonal shift toward wetter conditions would provide soil moisture and green‑up that reduce fuel flammability for weeks to months, but the benefit depends on spatial coverage and whether subsequent dry, windy periods follow.
The exact public‑safety outcome hinges on spatial variability. Rain concentrated offshore or northeast of urban basins would offer less benefit to coastal and lowland fuels while still producing flash‑flooding in mountain streams. Burn scars are of particular concern because wildfire removes vegetation that normally helps anchor soil; even modest heavy‑rate bursts—on the order of a half inch per hour—can rapidly generate destructive debris flows.
Economically, heavy rainfall and associated travel disruptions will affect holiday traffic and air travel: forecasters warned of gusty southeasterly winds that could delay arrivals and departures at Los Angeles International Airport. Infrastructure impacts could include localized road closures, swift‑water rescue needs if people are trapped in flood channels, and short‑term power outages from fallen trees or wind damage.
Comparison & Data
| Location | Most Likely Rainfall (Fri–Sun) | Last Year Oct–mid‑Nov (downtown L.A.) |
|---|---|---|
| Downtown Los Angeles | 2.62 in (scenario) | 0.07 in (2024 Oct–mid‑Nov) |
| Santa Barbara | 3.59 in | — |
| Oxnard | 2.49 in | — |
| San Diego | 1.5–2 in | — |
The table highlights the contrast between this forecasted event and last year’s early‑season drought indicators in downtown Los Angeles. While one storm cannot alter long‑term seasonal trends alone, crossing the 3‑ to 4‑inch threshold across broad low‑elevation areas would be a notable departure from the very dry conditions that preceded January 2024’s major fires.
Reactions & Quotes
“If we do end up getting the rainfall that we expect, this will certainly get us close to the end of the fire season.”
Ryan Kittell, National Weather Service (Oxnard)
Kittell framed the potential rainfall as a near‑term fire‑season relief while emphasizing that the exact outcome depends on totals and distribution. He and other forecasters stressed the continuing forecast uncertainty tied to the cut‑off low.
“There’s abnormally high amounts of uncertainty” about how the system will evolve, particularly for the Saturday peak.
Dave Munyan, National Weather Service (San Diego)
Munyan’s comment underscored why officials prepared evacuation warnings and closures despite differing possible rainfall scenarios. Transportation and emergency agencies cited the risk to communities below burn scars as the main driver for preemptive actions.
“Topanga Canyon Boulevard will be closed due to the high potential for heavy debris flows.”
California Department of Transportation (Caltrans, official notice)
Unconfirmed
- Whether the higher‑end 4.81‑inch scenario will materialize across broad low‑elevation areas remains unconfirmed and depends on the cut‑off low’s precise track.
- The probability and location of any brief tornadoes or localized damaging winds are uncertain; forecasters placed a small chance but could not specify exact targets.
- The extent to which this single storm will meaningfully change the remainder of the autumn and winter precipitation pattern is unknown; seasonal forecasts remain probabilistic.
Bottom Line
This storm presents a classic trade‑off for Southern California: a real chance to blunt an active fire season if widespread totals reach the 3–4 inch threshold, but a concurrent and immediate risk of hazardous flooding and debris flows—especially below recent burn scars. Residents in vulnerable canyons and foothill communities should follow evacuation orders, avoid travel through flood‑prone corridors, and prepare for road closures through the weekend.
For planners and emergency managers, the situation reinforces the need to weigh near‑term flood risk against the longer‑term wildfire benefits of substantial rainfall. Even if this event provides short‑term relief for fuels, sustained reductions in fire hazard require a sequence of wetter conditions and continued attention to wind events and infrastructure vulnerabilities.