California energy authorities are urging voluntary conservation of electricity as a wave of triple-digit heat strains the state's power grid.
The California Independent System Operator issued a so-called flex alert on Tuesday for 2 to 9 p.m., the period when air conditioners are typically at peak use and consumers should avoid running major appliances. Energy demand for the day was forecast to exceed 48,000 megawatts, which would be the highest demand on the grid so far this year.
The Los Angeles Department of Water and Power forecast a peak demand of 5,811 megawatts for the city, which would also be a record for the year.
The withering blast of broiling temperatures is being spawned by an area of upper-level high pressure over Nevada. "Just really, really hot this week, especially more than 5-10 miles inland from the beach," the National Weather Service office for the Los Angeles region wrote.
Excessive-heat warnings and heat watches blanketed inland regions from the Mexico border to the Oregon state line, up and down the Sacramento and San Joaquin valleys and west toward the Pacific—but stopped short of the coastline in most areas, especially the Bay Area, where sea breezes have brought what is expected to be a temporary cooling trend.
Red-flag warnings for fire danger are posted along the eastern flank of the Sierra Nevada because of the threat of dry lightning, and an air quality alert was issued for San Joaquin Valley counties because of smoke from a wildfire.
Long-range forecasts did not offer much prospect of relief.
"Out of the fire and into the frying pan for the weekend," the L.A. weather office said, predicting that the high pressure over Nevada will be replaced by a hot upper-level high moving into Northern California from the Pacific. "There is a chance that some areas will be hotter than they are now."
The San Francisco weather office said that despite that region's cooldown on Tuesday and Wednesday, there was increasing confidence that a new ridge of high pressure and high temperatures would be building late in the week and into the Labor Day weekend.
"Folks with any outdoor plans this upcoming weekend are urged to stay up to date with the latest forecast information in the coming days," said the weather service.