Heat wave to bring 90s to parts of Sonoma, Napa counties before chance of rain

Temperatures could reach as high as the upper 90s heading into the weekend across the inland North Bay thanks to a dayslong October heat wave that began building steam Wednesday.

The hottest days are expected to be Thursday and Friday, when the North Bay valleys will see highs in the upper 80s to lower 90s, said Dalton Behringer, a weather service meteorologist with National Weather Service’s Monterey office.

Santa Rosa is expected to reach 93 degrees Thursday and 92 Friday, while Cloverdale could peak at 94 Friday. The city of Napa was forecast to hit 90 on Thursday and Friday and Calistoga was expected to hit 92 Friday.

Higher terrain around Mount Saint Helena, where it won’t cool much overnight, will be in the upper 90s.

Nearer the coast, highs will be in the 70s.

“It’s going to be one of those days where the temperature can increase 10 to 15 degrees just by going a little bit inland,” Behringer said.

The smaller marine layer also means less ocean breeze, lower humidity and fewer clouds in interior areas.

By Wednesday morning, humidity dropped significantly due to overnight dry winds with gusts that got up to 60 mph near Mount Saint Helena.

Lighter ― about 10 to 12 mph ― offshore winds will continue to blow in the mornings and afternoons.

Behringer said all of these factors combined do make for heightened fire concerns but nothing close to the standards that need to be met for a red flag warning.

“Be mindful just because it’s going to be drier and it’s going be hot,” Behringer said, adding residents should avoid outside burning and other similar practices. “But it’s not a critical situation.”

While it may seem out of the norm, the upcoming heat spike is the type of event meteorologists expect this time of year, Behringer said.

The Cal Fire Sonoma-Lake-Napa unit and Santa Rosa Fire Department are not planning to set aside additional staff because conditions will likely not trigger a red flag warning from the weather service.

Cal Fire spokesperson Jason Clay said, however that the agency is at peak staffing, which will help if they need to respond quickly.

“We’re ready to go at any moment,” he said.

The more pressing concerns as of Wednesday are the heat effects, Behringer said.

“It’s definitely going to be impactful for those who are sensitive to the heat and those who don’t have air conditioning,” he said.

Residents should remember to check on their older and younger family members and do not leave dogs or kids in their cars in the heat.

After a hot few days, a cooling trend will begin Sunday as weaker cool air mass moves into the region. By Monday and Tuesday, temperatures will be closer to seasonal averages of the mid- to upper-70s.

A slight chance of rain is accompanying the cold front, Behringer said.

Regardless, the cooler temperatures will be a welcome change after the heat spike and, if any fires spark, will create conditions to discourage fire growth, Behringer said.

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