As triple-digit temperatures peaked across the North Bay on Thursday — Petaluma hit 101°F just after 1 p.m. — the Putah Fire in Yolo County, now in its fourth day of burning, reached 860 acres with roughly 30 percent of its perimeter still uncontrolled.

The Putah Fire is the sharpest local expression of what Cal Fire officials warned about all week: extreme heat creates the conditions for ignition, but the danger to vegetation doesn't disappear the moment temperatures drop. As the Bay Area finally cools into the mid-70s this weekend, the grass and shrub in Yolo County — and across the broader region — remains desiccated from weeks of dry heat, leaving fire crews in extended elevated-alert status.

Cal Fire's Battalion Chief Michael Sacheli, speaking Thursday as conditions peaked, was blunt about what crews were watching for: "Today's one of our hottest days, so we're concerned about starts," he told ABC7 News.

Although a Red Flag Warning that had covered Sonoma County expired Thursday, Sacheli said the underlying conditions driving fire risk — dry vegetation, low relative humidity, and residual heat — didn't expire with it. The North Bay is still playing with a live wire.

The Putah Fire, which ignited June 8 in Yolo County, confirms that concern in acres. Cal Fire's official incident archive lists it at 860 acres and 70 percent containment as of Friday — meaning roughly 258 acres of active perimeter remain uncontrolled. No homes or structures have been lost, and the agency reports a full deployment: engines, aircraft, hand crews, and bulldozers.

"We're fully staffed with all of our engines, aircraft, hand crews and dozers," Sacheli said.

That full-deployment posture reflects a 2026 fire season that has already logged more than 60,700 acres burned across the state — and the Putah Fire currently ranks among the 15 largest incidents on Cal Fire's active list. With the Northern California fire year typically peaking in late summer, the region is arriving at that window with parched fuel loads.

What the heat did to the Bay Area

Thursday's heat event was concentrated in the North Bay. In Petaluma, temperatures climbed to 101 degrees — an anomaly even for early June — with heat visibly distorting the air above the pavement. Santa Rosa residents adapted as best they could, flocking to the Finley Aquatics Center and adjusting outdoor activities.

The coast offered a different set of hazards. Beach hazard warnings were in effect at Ocean Beach in San Francisco and along the Pacifica shoreline, where parking lots filled quickly as heat-seeking residents drove west. Lt. Mariano Elias of the San Francisco Fire Department warned that coastal conditions — cold water, rip currents, unpredictable surge — don't respond to warm weather the way visitors sometimes assume.

"We want people to be aware that although it's nice to come to the water to cool off and get in and swim, they can be deadly," Lt. Elias told ABC7.

Ocean Beach has no permanent lifeguard staff; National Park Service ocean rescue personnel patrol the area during peak hours.

The cooling won't fix the fuel

National Weather Service forecasts show the Bay Area returning to more seasonal temperatures — highs in the mid-70s Friday through the weekend — a significant drop from Thursday's North Bay peak. For most residents, that means relief.

For fire agencies, it means lower ignition risk but no recovery in vegetation moisture. Grasses and brush that dried out over days of extreme heat won't rehydrate meaningfully from moderate temperatures alone. Cal Fire's elevated staffing posture isn't likely to scale back quickly.

The Putah Fire remains the clearest indicator of where things stand. Four days old, 860 acres, still burning.