California to get first major Diablo wind event of fall as fire danger ramps up.

Winds are expected to ramp up around Northern California the next few days, eventually resulting in critical fire weather conditions Thursday through Saturday. But before the elevated wildfire risk, a few rain showers are possible Wednesday as a weak cold front clips Northern California. The cold frontal disturbance is predicted to fizzle as it approaches the Bay Area because the parent storm is relatively far away over the Pacific Northwest, meaning rainfall totals will be light at best. 

Along this cold front, a few light rain showers could fall from San Francisco to Yuba City, but most areas will remain dry. Heavier showers, and a slight chance of thunderstorms, are possible in the northern Sierra Nevada north of Interstate 80. Behind this cold front, temperatures are expected to drop to near freezing around the Lake Tahoe Basin on Wednesday night. Even colder conditions are expected Thursday night, in the teens in Truckee and the low 20s along the Tahoe shoreline. In the Bay Area, Wednesday morning drizzle along the coast will be followed by afternoon clearing as winds gradually increase and mix out fog.

 

Northwest gusts up to 30 mph along the Peninsula will strengthen throughout the day and persist throughout the night. Fire danger will not be exceptionally high Wednesday due to the increased atmospheric moisture, but winds will begin blowing out of the north Thursday, drying out vegetation and increasing fire weather conditions. By Thursday night into Friday morning, winds are forecast to blow from the north-northeast. These are known as Diablo winds, and they have contributed to many of the Bay Area’s biggest wildfires. Because these winds blow over land, rather than water, they are much drier and pose a bigger fire risk than the typical sea breeze. 

Thursday through Saturday will be the first major Diablo wind event of the fall. Gusts up to 65 mph are possible along ridgetops in the North Bay and East Bay. There is more uncertainty as to how strong winds will get in the valleys, but periodic gusts of 25 to 45 mph are likely in Wine Country, the East Bay valleys and the Peninsula, including San Francisco. A wind advisory in Solano County and the delta region, including Sacramento, will go into effect at 11 p.m. Thursday, with gusts up to 55 mph expected. A red flag warning for heightened fire weather conditions is in effect for a large swath of the Bay Area from 11 p.m. Thursday until 5 p.m. Saturday. Pacific Gas & Electric Co. has warned that it could shut off electric power in order to prevent wildfires in parts of 30 counties starting Thursday.