SAN FRANCISCO (CBS SF) -- A weather system roaring toward the San Francisco Bay Area Sunday from the Great Basin triggered a Red Flag Warning for wind gusts reaching as high as 60 mph and humidity levels plunging into the teens -- a frightening combination for wildfires.
The National Weather Service said the culprit was what is known as an inside slider -- a low-pressure system that will approach the Bay Area from the east and not the typical path from the Pacific Ocean. Such a weather front typically triggers Diablo Winds -- the Bay Area's version of Southern California's treacherous Santa Ana Winds.
Forecasters said the warning will be in effect from Sunday afternoon until to Tuesday evening. Winds will begin gusting late Sunday afternoon in the North Bay and then move across the entire Bay Area after midnight.
"North to Northeast winds will be 15 to 25 mph with gusts 35 to 45 mph, locally higher gusts up to 60 mph," the weather service predicted. "Strongest winds are expected along the eastern areas of Napa, Contra Costa, and Alameda counties."
The shifting weather patterns so typical in October make the month a prime time for wildfires in Northern California.
Nearly 30 years ago, on a wind-swept Oct. 20th Sunday afternoon, a massive wildfire roared through residential areas of Oakland and Berkeley. It became known as the Oakland Hills Firestorm and stood as the most destructive fire in California history.
The historic blaze sparked to life on what used to be a vacant lot growing into a small brush fire that crews thought they had put out. But, after they left, the Diablo Winds began howling and smoldering embers became torches. In about an hour 800 houses had burned to the ground. Risa Nye's home was among them.
"We thought 'oh, it's never going to jump the freeway, how could it jump the freeway?' And then we went home and started throwing stuff in the car," Nye recalled.
In all, 3,300 homes were destroyed and 25 lives lost, including two first responders.
So Sunday's weather warning has local residents in the hills and firefighters more than a bit anxious. Drought parched hills covered with tinder-dry vegetation further elevates those concerns. Even the smallest fire could quickly grow into a massive, deadly wildfire.
"A Red Flag Warning means that critical fire weather conditions are either occurring now or will shortly," forecaster said. "A combination of strong winds, low relative humidity and warm temperatures can contribute to extreme fire behavior."
Given the threatening weather conditions, PG&E has been notifying tens of thousands of customers that it may shut off their power Monday due to elevated fire risk.
The utility announced Saturday that 44,000 customers in parts of 32 counties - including Alameda, Contra Costa, Napa, Solano and Sonoma counties - may lose electricity.
The potential Monday morning shutoffs could begin in portions of the North Valley, Sacramento, and San Joaquin Foothills. Potential shutoffs for the Northern Sierra Foothills, North Bay, North Coast regions, Bay Area hills and the Central Valley could begin Monday evening, depending on the timing of the wind event, the utility said.
Solano County is the Bay Area county with the most customers who could be affected by the outages with 4,559 customers and 423 Medical Baseline customers potentially impacted.
In Napa County, 2,207 customers and 107 Medical Baseline customers could be affected. The utility said 601 customers and 40 Medical Baseline customers could be affected in Contra Costa County, while 134 customers and 10 Medical Baseline customers could be affected in Alameda County.
The utility said 87 customers in Sonoma and one Medical Baseline customer could be affected.
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