National Weather Service issues North Bay wildfire weather watch starting Monday

A fire weather watch was issued for the North Bay mountains that will take effect late Monday night when gusty offshore winds and dry conditions are expected to combine to create potentially dangerous conditions, the National Weather Service said Sunday.

North to northeasterly winds could blow at speeds over 40 mph along higher ridges and peaks, spanning from the western edge of the North Bay to the Sacramento Valley and Sierra Nevada foothills. The strongest winds are expected overnight Monday and Tuesday.

The heightened wildfire conditions, from 11 p.m. Monday to 8 a.m. Wednesday, pose the greatest threat to the mountains in the eastern Sonoma Valley and across Napa County, meteorologist Roger Gass said.

The weather service is forecasting another spate of offshore winds later this week, indicating the conditions conducive for a fire could persist for a week or more.

“Given the dry conditions and fire season we’ve had and no measurable rainfall, we’re raising the alert to get people’s attention,” Gass said.

The weather pattern arriving Monday is not “an impressively strong event,” he said. But if the conditions worsen, the weather service could upgrade the watch to a red flag warning, elevating the potential for dangerous fire weather.

Brayden Murdock, a meteorologist with the National Weather Service, said Sunday night computer forecasting models were beginning to show conditions that could lead to a red flag warning. A decision on that won’t be made until after a conference call midmorning Monday with weather experts in regional agency offices.

Murdock said meteorologists are still reviewing expected conditions in the North Bay, and confidence in the modeling needs to increase before they can make a call on a red flag warning.

“With a red flag, we don’t typically send it out too far in advance,” he said. “Tomorrow, when we get our last batch of modeling data, and see what other offices are seeing (we’ll make a decision).”

Sustained winds are forecast to reach as high as 25 mph Monday night, and Tuesday night will be similar. Humidity could fall to its lowest levels Tuesday afternoon, but winds are expected to weaken by then. Meanwhile, vegetation on the ground is nearing record dryness, exacerbating the fire risk, according to the weather service.

A thin marine layer, peaking at about 300 feet over water, did little Sunday to ease dryness in the fire weather watch areas. Murdock said a deeper marine layer, perhaps reaching 1,500 feet and climbing further inland, could have brought needed moisture to the North Bay mountains and made a difference during the week.

The fire weather watch issued Sunday — when temperatures peaked at 92 degrees in Santa Rosa, 2 degrees shy of the record set in 1933, according to Accuweather — followed a prolonged red flag warning last week. It began Wednesday and was extended twice before expiring Saturday morning.

For part of that period, PG&E turned off power to about 1,700 customers in Sonoma County for nearly two days to avert a potential wildfire. The utility recorded peak winds at 73 mph in the county, a company spokesperson said.

A second wave of offshore winds in the North Bay mountains is expected later this week — with the strongest predicted on Saturday — so heightened awareness and vigilance is encouraged, Gass said.

Staff Writer Tyler Silvy contributed to this story.

You can reach Staff Writer Yousef Baig at 707-521-5390 or yousef.baig@pressdemocrat.com. On Twitter @YousefBaig.