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June 15, 2021 - FOLSOM, Calif. – The California Independent System Operator (ISO), as part of its commitment to prepare the public for possible stressed grid conditions caused by extreme hot weather, issued a Heat Bulletin in advance of high temperatures this week.

Although no outages or other power disruptions are anticipated right now, triple-digit heat is forecast to start spreading across California and the southwest Tuesday, June 15 through Friday, June 18, and the ISO could take a number of actions to reduce demand and access additional energy.

The ISO declared a grid Restricted Maintenance Operation (RMO) for noon to 10 p.m. from Tuesday, June 15, through Friday, June 18, due to forecasted high temperatures and demand. The RMO cautions market participants that all available resources are needed, and to defer scheduled maintenance on generators or transmission lines, if possible.

It is still too early to know the precise impact that next week’s high temperatures will have on the electric grid. But the ISO is closely monitoring conditions and the anticipated increase in demand for electricity and will issue additional public notifications as warranted.

Those notifications could include a series of steps aimed at reducing electricity use, such as a Flex Alert – a voluntary call for consumers to conserve electricity between 4 p.m. and 9 p.m. In extreme hot weather, those are the most difficult hours of the day to balance electricity supply and demand because solar resources are diminishing as more air conditioners and other home appliances are typically being used.

In the past, Californians responding to calls for conservation has significantly reduced stress on the grid and avoided further emergency actions, including the need to rely on reserve power resources or rotating outages.

But as happened during an intense regional heat wave last August that hit much of the Western U.S., rotating power outages could become necessary if weather and stressed grid conditions persist or worsen.

The public’s help is essential when extreme weather or other factors put heavy stress on California’s electric grid. Your cooperation can have a huge impact on our efforts to keep the grid strong and functioning properly and is greatly appreciated.

To review tips on conserving energy and sign up for notifications, visit

For the most up-to-date information on emergencies, you can follow us on Twitter at @California_ISO. More updates on System Conditions Bulletins will also be available on the News page of the California ISO website.

And please click here to learn more about System Alerts, Warnings and Emergencies. You can follow grid conditions in real time at ISO’s Today’s Outlook, or download the free ISO Today mobile app.
Source: CA. ISO