The National Weather Service has issued a red flag warning for Friday night through Sunday afternoon for the North Bay hills over 1,000 feet.
Winds on Friday night across the North Bay hills are expected to produce gusts of 40 to 50 mph over the highest peaks and temperatures on Saturday are forecast to be in the 90s.
Humidity will be 40-50 percent Friday night, dropping to 12-22 percent Saturday and 10 percent Sunday afternoon.
Winds will return Saturday but the low humidity will create critical fire weather conditions, the National Weather Service said. Fuels are not at critical levels but a weather event of this magnitude will allow fire to carry through finer fuels such as grass, officials said. Grass fires can spread rapidly and outdoor burning is not recommended.
Winds will ease Sunday but temperatures will be in the 90s to near 100 degrees with light offshore winds, the National Weather Service said. The highest threat is located along the hills of eastern Napa County and around Mt. Saint Helena.
The first red flag warning of the fire season prompted Pacific Gas and Electric to announce it might proactively turn off power in several Northern California counties within the next 18 to 36 hours to reduce the risk of wildfires. The possible shutoff includes the North Bay and Sierra foothills, PG&E said.
The potential power shutoff that would affect several thousands of customers in the North Bay includes portions of Napa and Lake Berryessa, portions of Suisun City, Vacaville and Winters and portions of Davis and Winters in Yolo County starting at 6 a.m. Saturday. The peak fire risk will last until 10 a.m. Sunday, according to PG&E.
PG&E said its goal is to send customer alerts through automated calls, texts and emails before shutting off power.