How hot the summer has been in Sonoma County and what that means for wildfires

National Weather Service meteorologist Sarah McCorkle said she believed summer was cooler than average this year in Sonoma County. She was surprised when she looked at the data.

One high-temperature record was broken, another matched, and overall temperatures were slightly above-average, she said.

Still, the summer was mostly uneventful, particularly considering wildfires. A lack of extreme heat waves allowed vegetation to retain moisture from the wet winter, resulting in fewer and smaller blazes.

Firefighters were able to spend more time preparing for the fall, which historically has seen the biggest wildfires.

From Jan. 1 to Monday, Cal Fire’s Sonoma-Lake-Napa Unit responded to 281 wildfires that burned a total of 561 acres across Sonoma, Napa, Lake, Solano and Yolo counties.

The largest blaze was the 103-acre Snell Fire in mid-June that spread through vegetation north of Pope Valley in Napa County.

In the same period last year, the agency had sent crews to 446 fires with a combined total of 2,634 acres.

Compared with previous years, there were fewer instances of extreme heat in the summer. And more troughs and cold fronts moved into the region to keep the marine layer intact longer and cool things down.

In June, the weather station in Santa Rosa recorded an average temperature of 74 degrees, which is 6 degrees below the all-time average of 80 degrees.

But there were some hot days. July and August both recorded an average high of 88 degrees, 5 degrees above normal.

In July, one record high was broken with temperatures reaching 104 degrees July 1 and one record was matched on July 16 with a high of 99 degrees.

September is on track for an average of 83 degrees, which is normal.

Also per typical, there was little to no rain during the summer, with the Charles M. Schulz-Sonoma County Airport last recording 1/100 of an inch June 12, McCorkle said.

“The winter moisture definitely helped us with that still,” she said. “We are not overly dried out with the heavier fuels... Grass fires are still a concern, but for widespread big fires, we are looking better than what we usually see this year.”

The weather conditions helped stymie any substantial fire threat.

The Santa Rosa Fire Department responded to 38 wildfire calls in the city, amounting to 3.19 acres burned and with no buildings affected.

There haven’t been any “major incidents” in the area, Santa Rosa Fire Chief Scott Westrope said.

Agencies could instead focus resources to mitigating fire spread, should blazes arise, and other preventative measures.

Cal Fire, for example, is preparing for prescribed burns, including about 60 acres of Trione-Annadel State Park and 40 acres in Jack London State Park, Cal Fire Division Chief Ben Nicholls said.

Weed abatement by residents also contributed to a lack of fires, Westrope said.

“We obviously can’t touch every home in Santa Rosa and so it’s incumbent upon everybody to do their part,” he said. “I really see the efforts, our prevention team really sees the efforts of what everybody is doing because it takes every link in the chain to be better.”

Fire agencies further prepared by getting new equipment to aid with fighting fires and improving communication.

The Cal Fire Sonoma-Lake-Napa Unit now has easy access to six aircraft, including two exclusive-use helicopters stationed in the Napa County Airport and the Charles M. Schulz-Sonoma County Airport. The unit also is in peak staffing, allowing for use of all 14 engines, two bulldozers, the Hood Mountain Fire Center and its aircraft.

The Santa Rosa Fire Department received new wildland personal protection and communications equipment and is expecting two new wildland engines delivered within the next month.

The agency has also set up new weather stations around the city to monitor the various micro-climates that have developed as the environment has changed, Westrope said.

“The amount of times we see a north or an east wind, the amount of times we see relative humidity drop down into the teens or single digits, the addition of dry lightning throughout our community ― these are all changes,” he said.

“It’s changed the way that we've had to approach everything in our industry, and we've had to do it very quickly.”

Autumn, which officially starts at 11:50 p.m. Friday, will get off to an uncertain start as a red flag warning, in effect through 5 p.m. Thursday, is followed by a strong possibility for rain early next week.

A low pressure system, closely resembling that of a bomb cyclone, is set to develop off the Pacific Northwest coast, about 800 miles north of San Francisco.

The reverb of the storm will roll into the North Bay beginning Monday through Tuesday morning, and will bring about 1/4 to 1/2 of an inch of rain, weather service meteorologist Rick Canepa said.

“That’s a lot of rain for September,” he said, which is typically the third driest month.

But it’s important everyone remain vigilant, Nichols said.

“Hope is not a good strategy,” he said. “We need to ... make sure that our communities are prepared and our firefighters are ready ready to go in the event of a major wildfire event.”

The last time Cal Fire saw a season like this ― with a good winter and a relatively quiet summer — was in 2019, Nichols said, when the Kincade Fire started that October in The Geysers northeast of Geyserville and burned 77,758 acres, destroying 374 structures.

Westrope said he approaches every season with hopes for the best but plans for the worst.

“We always prepare as if it is going to be the worst fire season ever and if we’re fortunate enough not to have that, great!,” he said. “But we always set ourselves up for those large-scale events and really to make sure that we are preventing them.”

“We’re supposed to have a pretty good rainy season again but we don’t know when it will start,” he added. “And things change quickly.”

You can reach Staff Writer Madison Smalstig at madison.smalstig@pressdemocrat.com. On Twitter @madi.smals.