Power to hundreds of thousands of homes and businesses is expected to go out, affecting millions of people in California, starting early Wednesday.

Pacific Gas and Electric Co. said a forecast of extreme wind and dry weather has created an unprecedented fire danger, prompting it to initiate the largest preventive outage in state history to reduce the risk of wildfires sparked by faulty power lines.

Here are some questions and answers about the outage.

Who is affected?


PG&E said it will turn off power to 800,000 customers — that means millions of people — in 34 counties in northern, central and coastal California. In Southern California, SoCal Edison warned that it might shut off power to more than 100,000 customers in eight counties as high winds are expected to hit the region Thursday.

The city of San Francisco isn’t covered by PG&E’s shutoffs. But much of the surrounding Bay Area and beyond could go dark, including large swaths of Silicon Valley, the cities of Oakland and Berkeley and much of the Northern California wine country hit by wildfires that killed 44 two years ago. The outage also affects parts of the agricultural Central Valley, the state’s northern and central coasts and the Sierra Nevada foothills, where a November wildfire blamed on PG&E transmission lines killed 85 people and devastated the town of Paradise.

How do Californians know if their power is going off?

PG&E said it was informing customers by text and email about where and when power would be cut. But its website, where it directed people to check whether their addresses would be affected, wasn’t working most of the day Tuesday after being overloaded with visitors. Local police departments and city and county officials were also sending auto-text and phone alerts as part of a system that local authorities urged residents to sign up for after last year’s devastating wildfires.


What about schools and public buildings?

Thousands of students were getting the day off Wednesday, and possibly Thursday, as school districts across Northern California announced plans to cancel classes. Some school districts in the power outage area, like Berkeley, said they planned to stay open Wednesday but told parents to stay tuned. The University of California, Berkeley, Sonoma State University and Mills College canceled classes Wednesday.

While critical emergency city and county services were expected to operate, residents were urged to call ahead about routine office hours as many may be closed. Hospitals have backup generators and could stay open, along with all emergency services. Cellphone companies have said most cellphones should work as long as they’re charged.

How are cities preparing?


Public agencies throughout the region urged people to stock up on bottled water and non-perishable food, fill their gas tanks, charge their phones and have cash at hand. People who need powered medical equipment or refrigerated medicines were urged to contact their providers. Authorities reminded people to park their vehicles outside garages or make sure they know how to manually open their garage doors. People also were warned to drive slowly and carefully because traffic lights could be out and roads closed.

Oakland Mayor Libby Schaaf asked residents not to clog 911 lines with non-emergencies.

Is there anywhere to go?

PG&E said it was opening more than 30 community resource centers to provide restrooms, electronic-device charging stations, bottled water and air-conditioned seating for up to 100 people. But the centers will only be open during daylight hours.


When exactly will the power go out? And for how long?

PG&E said it would start turning off the power in some areas just after midnight Wednesday. It will be switched off in stages, depending on the weather conditions in each area. The outage could last for up to five days. PG&E said it can’t switch the power back on until its equipment is inspected for damage and repaired. That process can’t begin until the severe weather conditions have subsided.