JOHN ANTCZAK and BRIAN MELLEY  / Associated Press

California’s governor declared a state of emergency Wednesday to increase power production and he urged residents to reduce electricity use as a heat wave spread over the West and officials warned there could possible outages if conditions worsen.

Gov. Gavin Newsom’s declaration followed a “Flex Alert” by the California Independent System Operator for conservation that was extended into Thursday as excessive-heat warnings expanded to all of Southern California and up into the Central Valley, where temperatures soared to triple digits. The heat was expected to spread into Northern California and blanket the state into next week, possibly breaking records in some places.

Temperatures that are expected to be 10 to 20 degrees above normal pushed up energy demand, primarily from air conditioning use, and tightened available power supplies. More alerts were likely through the Labor Day weekend, officials said.

Newsom declared an emergency to increase energy production and relaxed rules aimed at curbing air pollution and global warming gases. He emphasized the role climate change was playing in the heat wave.

“All of us have been trying to outrun Mother Nature, but it’s pretty clear Mother Nature has outrun us,” Newsom said. “The reality is we’re living in an era of extremes: extreme heat, extreme drought — and with the flooding we’re experiencing around the globe.”

Grid operators had not foreseen the need for an alert earlier in the day but conditions changed as the mercury rose, said Elliot Mainzer, president of Cal ISO.

Anticipated imports of hydropower from the Pacific Northwest and energy from the desert Southwest dried up because warmer weather in those regions had driven up demand there, Mainzer said. California also lost a “significant amount of internal generation “ in the state, though he wouldn’t say where that occurred.

Mainzer said power outages were a “possibility but not an inevitability,” especially if people cut back their electricity use.

Despite more than 160 projects to increase power supply and storage by 4,000 megawatts after outages two years ago, the the state’s power supply was partly crippled by the impact of the ongoing drought that has sapped a significant share of the state’s hydropower production as reservoir levels drop.

Newsom’s order allows use of backup diesel generators to put less strain on the system and won’t require ships at port to plug into onshore electricity sources. The move is expected to increase air pollution, but Karen Douglas, the governor’s senior energy adviser, said the priority was to keep the lights on.

The grid operator had said Tuesday that the need for voluntary conservation would be likely through the holiday weekend from 4 p.m. to 9 p.m. when the grid is most under stress and production of solar energy is declining. It said it was taking measures to bring all available energy resources online, including issuing an order restricting maintenance from noon to 10 p.m. daily through Sept. 6.

Cooling centers were being opened across the state and officials encouraged people to seek comfort at public libraries and stores — even if just for a few hours to prevent overheating.

The California Department of Forestry and Fire Protection was planning to stage fire crews in strategic locations, based on humidity and wind forecasts, said Mark Ghilarducci, director of the Office of Emergency Services.

Wildfires broke out in rural San Diego County and in Castaic in the Santa Clarita Valley north of Los Angeles, where some residents were told to evacuate.

Woodland Hills in the San Fernando Valley of Los Angeles set a new daily record of 112 degrees, breaking a 1998 record by 1 degree.

Peak load for electricity demand in California is projected to exceed 48,000 megawatts on Monday, the highest of the year, the grid operator said. It exceeded the demand forecast for Wednesday.

The primary ways to reduce household energy use are to raise thermostat temperatures, avoid using major appliances and electric car chargers, and turning off lights.

“If weather or grid conditions worsen, the ISO may issue a series of emergency notifications to access additional resources and prepare market participants and the public for potential energy shortages and the need to conserve,” Cal ISO said Tuesday.

The heat wave arrived amid concern about California’s power grid. In August 2020, a record heat wave caused a surge in power use for air conditioning that overtaxed the grid. That caused two consecutive nights of rolling blackouts, affecting hundreds of thousands of residential and business customers.

Newsom has proposed extending the life of the state’s last operating nuclear power plant by five years to maintain reliable power supplies in the climate change era. The proposal would keep Pacific Gas & Electric’s Diablo Canyon Nuclear Power Plant running beyond a scheduled closing by 2025.

Forecasters, meanwhile, warned of triple-digit temperatures with little overnight relief, as well as elevated risk of wildfires in much of the West.

“The big weather story this week will be a prolonged and possibly record heat wave building across much of the Western U.S.,” the National Weather Service wrote.