California ISO extends Flex Alert to Thursday, Sept. 1

Extreme heat continues urgent need to conserve electricity from 4 to 9 p.m.

FOLSOM, Calif. – The California Independent System Operator (ISO) has extended its statewide Flex Alert, calling for a second consecutive day of voluntary electricity conservation tomorrow, Thursday, Sept. 1, from 4 to 9 p.m., due to continuing extreme temperatures pushing up energy demand and tightening available power supplies.

With excessive heat in the forecast across much of the state and Western U.S., the grid operator is again expecting high electricity demand, primarily from air conditioning use, and is calling for the public to conserve as much electricity as possible from 4 to 9 p.m.

This is in addition to today’s Flex Alert, which is also in effect 4 to 9 p.m.

Additional Flex Alerts could be issued through the Labor Day weekend as triple-digit temperatures are forecast across much of California and the West.

In what’s likely to be the most extensive heat wave so far in the West this year, temperatures in Northern California are expected to be 10-20 degrees warmer than normal through Tuesday, Sept. 6. In Southern California, temperatures are expected to be 10-18 degrees warmer than normal. A majority of weather stations in California’s interior are poised to break their respective daily records over the holiday weekend, with the chance of monthly records being broken at a handful of stations.

The Flex Alert for Thursday, Sept. 1 is scheduled for 4 p.m. to 9 p.m., when the grid is most stressed from higher demand and less solar energy. During that time, consumers are urged to conserve power by setting thermostats to 78 degrees or higher, if health permits, avoiding use of major applicances and turning off unnecessary lights. They should also avoid charging electric vehicles while the Flex Alert is in effect.

To minimize discomfort and help with grid stability, consumers are also encouraged to pre-cool their homes and use major appliances and charge electric vehicles and electronic devices before 4 p.m., when conservation begins to become most critical.

Reducing energy use during a Flex Alert can help stabilize the power grid during tight supply conditions and prevent further emergency measures, including rotating power outages.

For information on Flex Alerts, and to find more electricity conservation tips, visit

Tips before a Flex Alert:

  • Pre-cool home by setting the thermostat to as low as 72 degrees
  • Use major appliances:
  • Washer and dryer
  • Dishwasher
  • Oven and stove for pre-cooking and preparing meals
  • Adjust blinds and drapes to cover windows
  • Tips during a Flex Alert from 4 p.m. to 9 p.m.:
  • Set thermostat to 78 degrees or higher, if health permits
  • Avoid using major appliances
  • Turn off all unnecessary lights
  • A Flex Alert is issued by the ISO when the electricity grid is under stress because of generation or transmission outages, or from persistent hot temperatures.

Follow developing grid conditions at the ISO’s News webpage, under the System Conditions Bulletin, or follow us on Twitter at @California_ISO.

Click here to learn more about System Alerts, Warnings and Emergencies. Follow grid conditions in real time at ISO’s Today’s Outlook, or download the free ISO Today mobile app.