No wind in the forecast — and the fuels don't care
The ridge holds through the weekend, and Southern California's fuels have come out the other side of it drier than normal almost everywhere. This is the kind of week where a fire gets big without any wind to blame.
Hello all — weather and fire update for Southern California.
Last week's heat is still with us. Strong high pressure stays parked over the West through the weekend and only starts to loosen its grip early next week, so the pattern doesn't really change — it just softens a little at the end.
The weather through next week
Expect temperatures running 5 to 10 degrees above normal into the weekend. That's mid-90s to around 105 in the valleys, 80s to low 90s nearer the coast and in the lower mountains, and 110 to 115 in the low deserts. Cooling starts early to mid-next week, mostly along the coast, and even then we stay near or above seasonal averages. Nobody gets a cold front out of this.
Afternoon humidity stays down in the 10 to 20 percent range across most of the interior. There's a wrinkle: monsoonal moisture is working in, so interior Southern California may run higher at times, more like 20 to 30 percent. Humidity comes up a little region-wide next week.
Winds stay light — ordinary daily onshore and terrain-driven flow, breezy in the afternoons and evenings, nothing organized. Onshore winds pick up slightly early next week. There is no offshore or Santa Ana signal in this forecast.
Starting Thursday, isolated showers and thunderstorms return to the mountains and deserts east and south of Interstate 15, and continue through the weekend and possibly into early next week. That activity may reach the high Sierra by the weekend.
The fuels — and why they're the story
This is the part worth reading twice. Hot, dry conditions away from the coast have kept an active burn environment in place all week, and the assessment is a substantially elevated risk of new large fires and active burning on existing ones — despite the lack of wind.
Dead fuel moistures are steady or still falling and are drier than normal in most areas. Live fuel moistures — the brush itself, which is supposed to be the wet part of the landscape in early August — are also on a falling trend. Energy Release Component, the standard measure of how much heat a fire in these fuels can put out, is above the 90th percentile across most of the region and above the 97th in several areas. Background fire danger in Southern California is rated very high.
What that adds up to in practice: wind is the ingredient people watch for, because wind events come with a name and a warning. This week has no wind event and the fire risk is high anyway. When fuels are this dry, an ordinary roadside ignition on an ordinary afternoon doesn't stay small while crews get to it — it establishes, resists containment, and grows on terrain and its own heat rather than on a wind push. Fires like that are also harder to read, because there's no dominant wind direction telling you where the thing is headed.
About those thunderstorms
The storms arriving Thursday look too isolated, too wet, and too confined to the high mountains and deserts to be a major ignition concern on their own. That's the honest read, and it's the one the fire agencies are going with.
It's still worth watching, for one reason: fuels coming out of this heat wave are extremely dry, so the margin for a dry strike in the wrong spot is thinner than the storm coverage alone suggests. Holdovers — a strike that smolders a day or two before it shows itself — are the specific thing to keep an eye out for in the days after a storm day, particularly east and south of the I-15 corridor.
Nothing in this forecast is dramatic, and that's exactly the trap. The fuels are doing the work this week, not the wind — so treat a quiet, hot, windless afternoon as a high-risk afternoon. Fires that start this week will be harder to catch than the weather makes them look.
For watches, warnings and advisories, the official source stays NWS California Fire Weather. One piece of context worth having: South Ops and North Ops are both at Preparedness Level 3 and the nation is at Level 5, so competition for crews and aircraft is real if something does start.
Any questions, just ask.