Red flag fire-weather warning issued for the weekend in Sonoma County

As expected for most of this week, the National Weather Service has issued a red flag warning from Saturday night to Monday, an alert that means critical fire weather conditions are coming.

The warning is triggered when weather brings a combination of strong winds, low relative humidity and warm temperatures, which can contribute to extreme fire behavior.

It will be in effect from 9 p.m. Saturday to 8 a.m. Monday.

Weekend temperatures are expected to be in the 90s to lower 100s, with Sunday the hotter of the two days.

The area under biggest threat will be the hills of northeast Sonoma County and Napa County above 1,000 feet, with the strongest winds near Mount St. Helena and at Mount Tamalpais in Marin County.

Any fires that develop will spread rapidly in the hot, dry and windy weather.

By Sunday night, the persistent drying offshore winds will reach the Sonoma Coast, including the Walbridge fire area.

Weather forecasters are predicting northeast winds of 15 to 25 mph Saturday night into early Sunday, with gusts from 35 to 50 mph above 1,000 feet elevation. Winds will ease during the daylight hours, but another burst of offshore winds will develop Sunday night into Monday morning. Those are expected to be almost purely offshore from the east.

Humidity is anticipated to be from 30% to 45% Saturday evening but will dry overnight as offshore winds develop. Moisture in the air will remain from 10 to 25% Sunday into early

Monday with no humidity recovery Sunday night, the weather service said.

You can reach Staff Writer Lori A. Carter at 707-521-5470 or lori.carter@pressdemocrat.com. On Twitter @loriacarter.