Fire weather in California — the wind, the fuel and the timing

This page is not a warning service

Golden State Weather explains mechanisms. It does not issue Red Flag Warnings, it does not track active incidents, and it does not know where you are. If there is a fire near you right now, use the official sources below and follow your county's evacuation instructions.

Everything on this page — and every safety link on this site — is free, permanently, and is not part of the Pro tier. That is enforced in the code, not just promised: capabilities marked as safety information cannot be placed behind a lock, and attempting it throws rather than shipping.

CAL FIRE incidentsActive fires, containment, evacuation orders National Weather ServiceRed Flag Warnings and forecasts NWS warning mapEvery active watch and warning Ready for WildfireEvacuation planning and defensible space AirNowSmoke and air quality right now Public Safety Power ShutoffsUtility de-energisation notices

Three ingredients, and the third is the one that matters

WHY SOME DAYS ARE DIFFERENT

California burns every year. What separates an ordinary fire season from a catastrophic fire day is not the presence of fuel or ignition — those are always available — but whether the atmosphere is doing three specific things at once.

01

Fuel that has not seen rain

California's Mediterranean climate means five to seven months with essentially no precipitation. By September the live fuel moisture in chaparral is at its annual low and the dead fuels are as dry as they get. The state's own climate builds the fuel bed; nothing unusual has to happen.

02

Humidity that collapses

Offshore flow brings air down from the Great Basin, and descending air warms about 5.5°F per 1,000 ft. Warming air holds far more moisture than it is carrying, so its relative humidity falls off a cliff — single digits are routine in a Santa Ana. Fine fuels equilibrate to that within hours.

03

Wind through a specific gap

The one that turns a fire into a disaster. Sustained 40–70 mph wind drives embers a mile or more ahead of the flaming front, which starts new fires faster than anything can be contained — and it grounds the aircraft that would otherwise fight them. This is why containment lines fail on wind days and hold on others.

The seasonal geography

WHERE AND WHEN, BY REGION

California does not have one fire season. It has several, and they run at different times because their ignition source and their wind regime differ.

Northern California — Jun to Oct Driven substantially by dry lightning. Thunderstorms move up over the Klamath, the Cascades and the northern Sierra with little rain reaching the ground, starting dozens of fires at once in country with few roads. The 2020 and 2021 sieges both began this way. KLAMATH · SHASTA CASCADE · SIERRA Bay Area & North Bay — Sep to Nov The Diablo wind season, peaking overnight when the marine layer has drained and the offshore gradient is strongest. The worst events land after the fuels have dried all summer and before the first rain has arrived. BAY AREA · NORTH COAST Southern California — Sep to Jan Santa Ana season, and the longest-running risk window in the state. If the first rains are late, December and even January Santa Anas arrive over fuel that has been drying for eight months. SOUTH COAST · INLAND EMPIRE · SAN DIEGO Santa Barbara — year-round The Sundowner makes this the one part of California with a genuine summer wind-driven fire risk, because the regime does not need the autumn pattern to run. TRANSVERSE RANGES The deserts — Apr to Aug A different problem: invasive annual grasses that cure early and carry fire across ground that historically did not burn at all. Monsoon lightning provides the ignition. MOJAVE · COLORADO DESERT After the fire — the debris flow A burn scar sheds water instead of absorbing it. The first intense rain over one can produce a debris flow with almost no warning time, and it is often deadlier than the fire. Montecito in January 2018 is the reference case. Burn-scar risk persists for several years. STATEWIDE · WINTER AFTER A BURN

What the warnings mean

TERMINOLOGY, SO THE OFFICIAL PRODUCTS READ CLEARLY

Definitions summarised from National Weather Service and CAL FIRE public guidance. Always follow the wording of the actual product for your area.
Term	Issued by	What it means
Fire Weather Watch	NWS	Critical fire-weather conditions are possible, usually 12–72 hours out. Time to prepare, not to act.
Red Flag Warning	NWS	Critical conditions are occurring or imminent — the wind, humidity and fuel thresholds are all met. Any ignition may spread rapidly.
Particularly Dangerous Situation	NWS	A rarely-used tag added to a Red Flag Warning for the most extreme events. Treat it as the strongest wording the service has.
Public Safety Power Shutoff	Utilities	Pre-emptive de-energisation of lines during high fire risk. Not a warning about a fire; a measure to avoid starting one.
Evacuation Warning	County / CAL FIRE	Leave if you need extra time, have livestock, or have any reason to move slowly. Do not wait for it to become an order.
Evacuation Order	County / CAL FIRE	Immediate threat to life. Leave now, by the route given.

Where the wind comes from

Every regime named on this page is explained in full — the pressure pattern that switches it on, the canyon or ridge it comes through, and the hours it peaks — on the wind regimes page. Each region page lists its own forecast offices.

FIRE WEATHER