Californians were urged by energy regulators to use less power in the coming days, as "record demand" on the state's energy grid is expected.
The heat wave means that air conditioners are on in "PG&E's vast northern and Central California territory," according to reports, which add that the need for electricty is at "record" levels.
The record demand for electricty also comes at a time when there is less power available. PG&E's Diablo Canyon nuclear reactor is out for maintenance, the utility reports.
Consumers are asked to cut their power use between noon and 7 p.m., the San Jose Mercury News reported.
Peak demand is expected to reach 47,000 megawatts by 4:30 p.m. Monday, the newspaper reported.
Citizens should turn off lights and only run dishwashers and washing machines in the evening hours, according to CalISO, the California Independent System Operator, which monitors the electricity grid.