SAN FRANCISCO >> Pacific Gas & Electric Co. turned off electricity today for about 170,000 people in Northern California to prevent power lines from sparking wildfires as the region faced a new bout of windy and warm weather.

The utility originally said that about 150,000 customers, or about 375,000 people, would be affected by the outages but significantly lowered that number after some areas got rain or increased humidity that lowered the fire threat.

Vanrenen said about 35,000 more people were told they could lose power later today if weather conditions do not improve in their communities. People who lost power were expected to get it back Thursday.

A virtually rainless fall has left brush bone-dry and forecasts called for low humidity and winds gusting at times to 55 mph, which might fling tree branches or other debris into power lines, causing sparks that could set catastrophic fires in the region, PG&E officials said.

The blackout is the latest in a series of massive outages by the country’s largest utility, including one last month that affected nearly 2.5 million people and outraged local officials and customers who accused the utility of overkill. Officials have accused the company of using the blackouts as a crutch after years of failing to harden its infrastructure to withstand fire weather.

PG&E CEO Andy Vesey acknowledged the outages have been “terribly disruptive” and said the company is taking steps to avoid them in the future, but for now, “we won’t roll the dice on public safety.”

Meanwhile, California’s utility regulators are demanding answers from wireless, internet and landline providers whose equipment failed during previous outages, leaving hundreds of thousands of people without a way to get emergency alerts or make 911 calls.

Representatives from eight communications companies, including AT&T, Comcast/Xfinity, T-Mobile and Sprint, appeared before the California Public Utilities Commission Wednesday, fielding questions about whether they would support a rule requiring backup power and whether they would disclose outage information publicly and immediately during disaster situations.

Verizon, T-Mobile and AT&T officials said they would disclose outage information.

In a letter calling for the meeting, commission President Marybel Batjer said “lack of service is not a mere inconvenience— it endangers lives.” She said residents do not have the luxury of failed internet or cellphone connections during a wildfire or other disaster.

Some local public officials who planned to speak at the hearing could not because of the latest power outage. And Lake County Supervisor Moke Simon made comments before rushing back to Northern California county, where the lights had gone out again.

He said AT&T’s network went down right away during an outage in late October, risking the county’s sewer and alarm systems. There was no backup in place, he said.

“That really put us in a dire straits situation,” he said.

Batjer told communications company representatives she was surprised by their lack of preparation given California’s long history of wildfires.

“It’s sort of stunning that you go, ‘Well, we just learned a lot in the last three weeks,’” she said.

More than 450,000 people were left without communications, according to a group representing rural counties in California. Half of Marin County’s cell sites were out of service.

Consumer advocates urged the commission to establish backup power requirements and make the companies provide detailed information about outage locations.

The California Governor’s Office of Emergency Services has called the companies’ level of engagement unacceptable at a time when redundant infrastructure is necessary.

In written responses in advance of Wednesday’s meetings, the companies said they did communicate with authorities but the outages were unprecedented in scope. The companies said they are improving backup power sources but added that doing so might not be possible in some locations and that generators are not always safe.

Comcast said that its network “like any modern network, fundamentally relies on commercial power to operate.”

Meanwhile, warnings of extreme fire danger covered a large area. California’s state fire agency placed fire engines and crews in position in some counties and had crews ready to staff aircraft and bulldozers.

The weather was expected to ease by Thursday morning, allowing PG&E to begin restoring power, said Mark Quinlan, PG&E’s senior director of emergency preparedness and response.