A dangerous combination of fast winds and low humidity at the height of fire season is expected to prompt power outages for tens of thousands of Northern California homes and businesses starting Wednesday and lasting potentially into Friday.
PG&E apprentice Oscar Rodulfo works to restore power along Los Alamos Road in Santa Rosa, where shut-offs are possible.
Pacific Gas and Electric Co. has warned that about 54,000 customers in portions of 24 counties, including most Bay Area counties, will likely face preemptive electricity cuts intended to prevent wildfires caused by wind-damaged power lines.
Generators and other measures deployed by PG&E should keep the lights on for about 12,000 customers that would have otherwise lost power, according to Mark Quinlan, the company’s incident commander.
PG&E officials did not expect to make a final call about shutting off power lines until Wednesday morning. But if the forecast materializes as expected, electricity will go out mainly in two waves later that day, with a third possible on Thursday.
The shut-offs were expected to begin at 6 p.m. Wednesday for 33,000 homes and businesses, primarily in the North Bay and northern Sierra Nevada foothills. Two hours later, the outages would move farther south into the Sierra as well as targeted spots in the East Bay, South Bay, Peninsula and Central Coast.
Limited areas of Humboldt and Trinity counties could lose power late Thursday afternoon as the second of two rounds of anticipated Diablo winds blow through, PG&E said.
Electric service should be restored for everyone no later than Friday at 10 p.m. But company officials said they would look for opportunities to turn some lines back on sooner or narrow the scope of the shut-off event.
“All of this is based on forecasted weather,” Quinlan said during a public briefing. “Forecasts can change, and we will change with those forecasts and make the appropriate decisions.”
The looming blackouts come as the National Weather Service issued a red-flag warning of extreme fire danger from 5 a.m. Wednesday through 11 a.m. Friday. It applies to the North Bay valleys and mountains, the East Bay valleys and hills and the Santa Cruz Mountains, forecasters said.
The highest winds — with gusts of up to 55 mph — are expected Wednesday night into Thursday morning with another bout of slightly less powerful winds overnight Thursday.
The winds, sweeping from the north and northeast toward the coast, are expected to suck the moisture out of the air, causing humidity levels to drop as low as 10% during the day and to remain low overnight. In Napa County, on Atlas Peak and Mount Veeder, humidity could drop to a bone-dry 15% with gusts of 40 mph Wednesday night, according to the Weather Service.
Those conditions greatly elevate the chance that winds could damage PG&E electrical equipment and start a major wildfire, as has happened repeatedly in years past.
PG&E is once again turning to fire-prevention blackouts, hoping to avoid causing more disasters. The company and its parent PG&E Corp. recently emerged from a hard-fought bankruptcy case prompted by their responsibility for several years of fires. And state investigators are investigating whether the company’s equipment sparked yet another blaze, the deadly Zogg Fire in Shasta County that ignited on Sept. 27.
“We have had a historic fire season this year,” said PG&E meteorologist Scott Strunfel. “We are and will continue to be in the peak of fire season until the rain and snow returns. And all of us here hope that it returns sooner rather than later.”
This week’s fire-prevention blackouts are not expected to be as bad as late October 2019, when the company turned off electricity for millions of people, many of them for days.
PG&E endured scathing critiques last October because of how many people lost power and how poorly the company communicated with its customers. Since then, the company has sought to improve its shut-off program in various ways, including through equipment upgrades that allow it to isolate more narrow portions of the grid.
The company has also set up temporary microgrids that can let electricity continue flowing in commercial corridors while power is out in surrounding areas. Generators plugged into certain substations can keep the lights on for some customers even if the power lines connected to the facility are turned off because of fire risk.
Both of those could come into play this week in Calistoga, which has been repeatedly subjected to PG&E’s preemptive outages.
City Manager Mike Kirn said local officials had worked with PG&E to get a cluster of generators set up for a microgrid based at a property that is normally used as an off-leash dog park. He anticipated that the arrangement could keep power flowing to much of Calistoga east of the Napa River.
“It’s very positive, otherwise we’d be 100% out of power,” Kirn said. “We’re encouraged by the efforts that PG&E has put forward, and hopefully this one will be much smoother than the last one.”
The generator-powered microgrid could keep power on at about 1,500 homes and businesses in the downtown Calistoga area, though nearly 2,300 customers with Calistoga addresses would remain within the scope of the shut-offs, according to PG&E. Generators at the Calistoga substation may help maintain electricity for homes beyond the boundaries of the microgrid.
Warm, but not extreme, temperatures are expected to accompany the dry winds, according to the Weather Service. Meteorologists have not issued an extreme heat advisory but expect that high temperatures in San Francisco will be in upper 70s to low 80s from the coast to the bay, an uncomfortable range for a city where air conditioning is uncommon.
Inland, in the North Bay and outer reaches of the East Bay, highs will reach into the mid- to upper-90s but probably stop short of 100 degrees. Highs around the bay shoreline are also expected to be in the mid-80s.
“It will definitely be warm in the Bay Area,” said Cindy Palmer, a Weather Service meteorologist.
Both the high winds and warm temperatures are likely to remain until Friday with cooling arriving over the weekend.