Bystanders help move a stranded motorist near Bear Valley Outerhighway South, Tuesday, Sept. 8, 2015, in Hesperia, Calif. (David Pardo/The Victor Valley Daily Press via AP) MANDATORY CREDIT
LOS ANGELES - LOS ANGELES (AP) — Much of California simmered in a stew of high heat and humidity on Thursday, bracing for more thunderstorms and flash floods that have already killed one person and left scattered damage and power outages.
The sweltering, erratic weather was being generated by a ridge of high pressure over the state and the monsoonal flow of moisture from Tropical Storm Linda, the weakening former hurricane spinning in the Pacific about 400 miles southwest of San Diego.
Thursday was expected to be the peak of the weeklong heat wave, which has produced triple-digit temperatures up and down the state.
Heat advisories extended from San Diego north to San Francisco and beyond, although fog that swaddled the Golden Gate and cooler temperatures along the immediate Bay Area coast presaged a gradual return to normal summer weather.
Cloud cover knocked a degree or two off high temperatures, but the National Weather Service said it would not be noticeable because of the high humidity.
Demand for electricity, meanwhile, was high as people turned to air conditioning for relief.
"Yesterday's usage was close to Southern California Edison's peak usage on Aug. 31, 2007," utility spokesman Paul Griffo said.
Power outages resulting from extreme heat and thunderstorms continued to affect residents.
Outages affected more than 15,000 Southern California Edison customers early Thursday morning; by midday, about 8,100 of the utility's customers were without electricity, Griffo said. San Bernardino, Riverside and Los Angeles counties were the hardest hit areas.
In Los Angeles, 1,700 customers, mostly in the downtown area, were without electricity, Department of Water and Power spokeswoman Ellen Cheng said.
There were just a few hundred heat-related power outages among the 5 million Northern California customers served by Pacific Gas and Electric, utility spokesman Matt Nauman said.
Afternoon thunderstorms and resulting flash-flooding also left damage.
A section of State Route 2 in the San Gabriel Mountains northeast of Los Angeles was closed indefinitely because of a massive rock-and- mud slide triggered by a downpour on Wednesday evening. The California Department of Transportation estimated the debris between Islip Saddle and Vincent Gap amounted to 150 truckloads.
A 25-year-old man was killed earlier in the week when he was swept to his death by a rain-swollen creek in the Forest Falls area of the San Bernardino National Forest. An off-duty sheriff's deputy saved the victim's companion.
Forecasters, meanwhile, said the end of the oppressive weather was in sight but wouldn't happen overnight.
The high-pressure system bringing the heat will slowly weaken through Saturday while the tropical storm off Mexico also weakens, the weather service said. A trough of low pressure developing off the Northern California coast will be followed by an even deeper trough next week and there will be a gradual shift away from the hot and humid pattern, with thunderstorms restricted to the mountains and deserts.
The last day of the thunderstorm threat will be on Sunday, the National Weather Service office in San Diego said.