SAN FRANCISCO - The California Independent System Operator (ISO) declared a "Stage 2" power emergency late on Saturday, warning that rotating power outages were possible amid a record heat wave.
A Stage 2 power emergency means the ISO has taken all mitigating actions but can no longer provide its expected energy requirements.
Temperatures of up to 125 degrees Fahrenheit (49 Celsius) were set to punish California through the Labor Day weekend, raising the risk of wildfires and rolling blackouts.
California Governor Gavin Newsom on Friday declared a state of emergency, a proclamation that allows power plants to operate beyond normal limits through the three-day holiday weekend.
The National Weather Service (NWS) forecast a heat wave carrying "rare, dangerous and very possibly fatal" temperatures across Southern California for the holiday weekend.
State officials urged Californians to turn off unnecessary appliances and lights to help avoid blackouts from an overwhelmed power grid.
Authorities also asked power generators to delay any maintenance until after the weekend to prevent blackouts like the two nights of rolling outages in mid-August as residents cranked up their air conditioning.
This weekend was expected to be hotter than the one in mid-August that helped trigger the second- and third-largest forest fires in California history. Those fires are still burning.
Death Valley in California's Mojave desert registered one of the hottest air temperatures recorded on the planet of 130F (54C) on Aug. 17, and highs of around 124 were expected there on Sunday, the NWS said.
San Francisco-based power provider PG&E Corp said on Saturday that it may be asked by the grid operator to turn off power due to the "extreme heat." It urged customers to conserve power.
The company said it may have to cut power early on Monday and Tuesday in parts of Northern California as hot, dry winds are expected to threaten the region.
PG&E said its potential power shut-offs may impact parts of 17 counties, which would include about 103 000 customers.