California is facing worsening power grid challenges on Monday and Tuesday.
According to the California Independent System Operator (ISO), demand for power is approaching record levels.
The grid operator called for even greater reductions in electricity use, with historic heat bearing down on the Golden State over the next several days.
"Starting tomorrow, this multi-day event is going to get much more intense," ISO CEO Elliot Mainzer said in a statement. "We are facing a load forecast of 48,817 megawatts and energy deficits between 2,000 and 4,000 megawatts for Monday, resulting in the highest likelihood of rotating outages we have seen so far this summer."
"Because of the increasingly extreme conditions, we will need significant additional consumer demand reductions during the hours of 4 p.m. to 10 p.m. on Monday and access to all the emergency tools that the state and utilities have established for an extreme event like this one. We thank electricity consumers for their sustained effort to help us maintain reliability during these very difficult conditions," he said.
It is the sixth consecutive day of ISO's statewide Flex Alerts, which call on consumers to cut electricity use from 4 to 10 p.m. PT as well as set thermostats to 78 degrees or higher and avoid using major appliances.
While previous alerts were issued through 9 p.m., the ISO said the extra hour of reduced energy use was necessary due to projected market deficiencies.
Additional calls for reducing energy consumption are expected as record-breaking temperatures last at least through Friday.
Savings have already resulted in an estimated 600 to 700-megawatt savings in recent days.
Several generators are already out of service, making supplies tighter.
Daytime high temperatures are forecast to be 10 to 20 degrees above normal, with the highest heat on Tuesday.
California Gov. Gavin Newsom signed an executive order last week that will allow his state to ramp up its electricity supply.