After a relatively mild summer and a temperate start to fall, the perils of potentially hazardous fire conditions will return to the Bay Area this weekend.
On Saturday and Sunday — with wind gusts that the National Weather Service anticipates to be at least 50 mph, driving an air mass that’s drier than usual over vegetation still overgrown from last winter’s rain — fire danger is expected to be front and center again.
“Simply put,” NWS meteorologist Matt Mehle said, “this is a big giant heads-up.”
The weather service early Friday issued a fire weather watch and wind advisory for the Santa Clara Hills, East Bay Hills, Santa Cruz Mountains, Marin Coastal Range and the North Bay Interior Mountains that will be in effect Saturday and Sunday. Mehle said the fire weather watch likely will be elevated into a red flag warning before the weekend begins.
Among the chief concerns, according to the weather service, will be the ability of any small spark to start a blaze and spread quickly. Trees and power lines also could suffer damage in the winds, the agency said.
Then there’s the sheer volume of vegetation.
“The fuels are going to get really dried out, and there’s a lot of fuel,” Mehle said. “So whenever you have that much vegetation and it’s going to be as dry as it is, that’s a big concern.”
Messages left for local fire officials early Friday were not returned immediately.
The dangerous conditions are the result of an extremely dry air mass that’s moving through the region from the north. The offshore winds that are such a regular part of the Bay Area weather pattern will remain, Mehle said. He added that their direction in this pattern will lead them to go down the slope of mountain ranges, further speeding up the evaporation of moisture.
“If you were to compare this air mass to other air masses we get, this one would be much drier,” he said. “It’s a colder source that’s sending it. It has a cold path, and that tends to dry out the air.”
Also, the winds may prove to be far more powerful than early estimates.
“I wouldn’t be surprised to see gusts get up to 60, maybe 70 mph in the highest spots, especially in the East Bay and North Bay mountains,” Mehle said.
All of this will come amid temperatures that will be signal that sweater weather is here. The hottest spots in the region are expected to peak at 74 on Sunday. Overnight lows are expected to dip into the low 40s.
By Monday, the winds will be gone, air with a bit more humidity will be back and “it will be a return to normal,” Mehle said.
This is a developing report. Please check back for updates.