California’s energy supplier has warned the continued historic heatwave is set to see power outages as the state’s electricity grid becomes overloaded.

As the US National Weather Services warned residents to stay indoors adding heat levels this week will pose a threat to vulnerable individuals, the CEO of the California Independent System Operator (ISO) has warned that power supply is under extreme threat.

The ISO has reiterated an earlier call for consumers to lower electricity use in the afternoons and evenings to avoid outages.

“Starting Monday, this multi-day event is going to get much more intense,” said ISO president and CEO Elliot Mainzer. “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.”

The ISO has issued a state wide Flex Alert, its sixth straight day calling for consumers to cut their electricity use and have been urged to set thermostats to 78 degrees or higher, avoid using major appliances, and turn off all unnecessary lights.

Additional calls for reducing energy consumption are expected as the state endures record-breaking temperatures lasting at least until Saturday.

“The heat wave is historic for both its temperatures and its duration,” The ISO added. “Heat advisories and excessive heat warnings are in place across the West, with daytime high temperatures forecast to be 10-20 degrees above normal. Electricity customers’ actions to cut their demand have already resulted in an estimated 600 to 700-megawatt savings in recent days and are expected to be even more important and impactful through the next several days.

“Power grid conditions are expected to be strained this evening, with a potential for supply shortfalls.”

Yesterday and today are projected to be the most challenging days yet, with the highest temperatures forecast today and projected electricity demand of 50,099 megawatts (MW).

Grid operators said they are closely monitoring wildfires for potential threats to generators and transmission wires, and fire officials have warned that more fires could break out in the coming days, due to the prolonged high heat and dry conditions. However, several generators are already out of service, putting further pressure on supplies.