Red flag warning issued for North Bay hills this weekend

The National Weather Service on Friday issued a red flag warning for the North Bay hills this weekend, reflecting an early start to the type of critical weather conditions that can fuel catastrophic wildfires in the region.

Offshore winds, low humidity and expected warm temperatures prompted the alert, starting at 11 p.m. Friday through 6 a.m. Monday. Upper elevations in the East Bay are also affected.

While PG&E’s meteorology team is closely monitoring conditions, no public safety power shutoffs are anticipated at this time, said Tamar Sarkissian, a spokesperson for the utility.

Most of Northern California is experiencing severe drought after a second historically dry winter. Moisture levels in fuels are at near record lows for this time of year, and other indicators of fire intensity show that conditions on the ground are already what might be expected in June of a more normal year.

The last time the National Weather Service issued such a heightened alert for this part of the state so early in the fire season was in May 2013, according to Ryan Walbrun, a meteorologist for the service.

“It’s not unprecedented, but it sure is rare,” Walbrun said.

A map posted on the National Weather Service website and one shared by the County of Sonoma on social media showed the red flag warning covering parts of northwest Sonoma County along the coast.

Although that area was initially shown as covered by the red flag warning because of a technological error, the Weather Service on Saturday made the decision to expand the red flag alert to coastal areas because the erroneous map had been shared so widely, a meteorologist said Saturday.

Forecasts call for a burst of offshore winds expected to reach the Napa County hills and Mayacamas Mountains around 11 p.m. Friday night. Those gusts, along with low relative humidity, will further dry out fuels that are already parched following a second winter with paltry rainfall, Walbrun said.

Another concern, he added, are the “pretty warm to hot temperatures” — upper 80s to lower 90s — expected in the Sonoma region this weekend. “When all those elements line up, that kind of becomes a trigger point for issuing red flag warnings.”

Walbrun pointed out that this weekend’s winds, while strong enough to necessitate the high alert, will not be as powerful as the gusts that came down the Mayacamas in September and October 2020. Those winds fueled the Glass fire that spread from western Napa County into Sonoma County, where flames ran roughshod over rural properties and subdivisions on Santa Rosa’s eastern outskirts, destroying more than 330 homes.

“I think it’s important to differentiate that this should be a moderate strength event,” he said. “We think the strongest winds are going to stay up in the hills. It’s not a pattern where they’re going to mix down into the lower regions, like Santa Rosa proper.”

Walbrun said he and his colleagues at the weather service have talked to some fire agencies, who are urging people to “be smart this weekend with any ignition sources.”

“This might not be the time to do your defensive space work,” he said, “especially if it involves lawn mowers or chainsaws.”

Staff Writer Nashelly Chavez contributed to this report. You can reach Staff Writer Austin Murphy at 707-521-5214 or austin.murphy@pressdemocrat.com or on Twitter @ausmurph88.