An intense heatwave covering much of the western US and bone-dry conditions across California forced rolling blackouts for the first time in a decade and fuelled wildfires that threatened thousands of homes.
Electrical demand surged on Friday as residents dialled up air-conditioning units and fans, prompting the California Independent System Operator, the body that manages the state's power grid, to declare a "stage 3 emergency" that evening, forcing utilities to cut power to hundreds of thousands of residents in the state.
California's utilities companies were ordered to implement rotating power outages to protect the grid's stability. It marked the first time such an order had been in place since 2011. Pacific Gas & Electric, the state's largest utility, announced it was cutting off power to as many as 250,000 people in rotating outages.
"Extreme heat" was driving demand for electricity, according to Anne Gonzales, a spokeswoman for the state's grid operator told the Associated Press. The agency said that the heatwave throughout the region has impeded the state's ability to rely on other power from outside the state.
Temperatures could reach as high as 112 degrees (44.4 Celsius) across the state over the weekend, the National Weather Service has warned.
The blackout order was lifted before 9pm on Friday and power was restored to affected households before midnight.
But the heat wave is forecast to extend through next week, with the National Weather Service declaring excessive heat watches and warnings and heat advisories for much of the western US. More than 2 million people were affected by preemptive power shutoffs in 2019 as electrical malfunction and high winds with dry conditions threatened wildfires in northern California.
"While temperatures in Texas will gradually moderate closer to normal during the next couple of days, the heat will expand and intensify across the interior Pacific Northwest into the Great Basin where widespread record high temperatures will be likely for the coming days," the National Weather Service announced on Saturday. "Actual high temperatures are forecast to top 100 degrees at many locations, along with a heightened risk of wildfires."
Fires in Angeles National Lake Forest outside Los Angeles threatened thousands of homes and more than 27 miles (70 km) of brush and forestry as firefighters worked to contain the blaze in temperatures reaching 100 degrees (38 Celsius) on Friday, fire officials reported.
The so-called Lake Fire forced hundreds of evacuations and damaged at least 21 structures, according to fire officials.
It has spread to more than 17,000 acres after the blaze erupted on Wednesday. The US Forest Service believes it may have been caused by human activity.
Firefighters are actively responding to several fires in the state, the largest of which is the Apple fire, which has burned more than 33,00 acres after it was sparked on 31 July.
Law enforcement in Azusa, California are searching for a man who is believed to have intentionally started a 2,500-acre fire in Los Angeles County. Osmin Palencia, 36, is wanted for arson in connection with a blaze that erupted on Thursday.
More than 80 million people were under heat alerts on Friday, extending from the central part of the US through the entire West Coast. Affected cities include Dallas, Houston, Phoenix, Las Vegas, Los Angeles, Portland and Seattle, as well as most of California.
Climate change also has accelerated the risk of heatwaves and wildfires, as dry vegetation and fierce winds prime conditions for deadly fires.
Heat has contributed to the deaths of more than 600 people in the US each year, according to the Centres for Disease Control and Prevention.
While public health officials are urging people to stay home during the coronavirus pandemic, utilities are seeing surges in electricity use. While California has activated cooling centres to assist people in need, officials also are concerned that prolonged congregation could increase the risk of Covid-19 transmission.