The National Weather Service (NWS) warns that hot and dry weather this week could spark fires across Northern California, including the entirety of North Bay, East Bay, and South Bay, A red flag warning will be in effect from September 23 through September 25.
While the bulk of the warning covers places further north like Sacramento County and Butte County, the impact area also includes parts of Marin County, Napa County, Sonoma County, Contra Costa County, Santa Clara County, and Alameda County.
The forecast calls for “gusty north to east wind” up to 25 miles per hour, with gusts up to 40 miles per hour at some times, combining with high temperatures to create “critical fire weather conditions.”
The forecast also warns that “any fires that develop will likely spread rapidly.”
A red flag warning usually means a trifecta of potential dangers in the relevant area: warm temperatures, low humidity, and strong winds, which together create a formula for aggressive fires.
Cal Fire says that a variety of common activities might create or spread a fire, including mowing dry grass or letting vegetation overgrow areas within 100 feet of homes. Even pulling a car over into a dry, grassy area could ignite a blaze.
So far in 2019, Cal Fire and the Forest Service combined record just 151,681 acres burned from wildfires, less than half of the five-year average for just Cal Fire, and less than a quarter of the 2018 burns this time last year.
But new fires may start at any time, and September and October have historically proven dangerous for wildfire threats.