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As a heat wave passes through much of California, a statewide Flex Alert is in effect from 4 p.m. to 9 p.m. both Friday and Saturday.

A Flex Alert is a call to residents to voluntarily conserve energy when demand for power could outstrip supply — which generally occurs during heat waves — to avoid power disruptions and rolling blackouts, according to the California Independent System Operator, which runs most of the state’s electric grid.

If demand still outstrips supply after the Flex Alert is in effect, the ISO can order state utilities to reduce demand by implementing rotating power outages of relatively short duration to extend the available electricity as much as possible, the agency said.

The Flex Alert was originally only in place for Friday, but it was extended for a second day, from 4 p.m. to 9 p.m. Saturday, as extreme heat in California and a growing wildfire in southern Oregon threatened transmission lines and strained the state’s electric grid.

The ISO also issued a warning Friday due to wildfire risks, indicating that grid operators anticipate using electricity reserves.

Before the Flex Alert takes effect and when solar energy is abundant, residents are encouraged to take these steps to be comfortable and help grid operators balance supply and demand:

  • Pre-cool your home by lowering the thermostat to 72 degrees
  • If you need to use your major appliances, do it before the Flex Alert is in effect, when solar energy is plentiful
  • Close blinds and drapes to keep the heat out of your home or apartment
  • Charge electronic devices and electric vehicles so there’s no need to do it later

During the Flex Alert period, consumers are encouraged to:

  • Set thermostats to 78 degrees or higher, or use fans to cool the home, if your health permits
  • Avoid using major appliances, like dishwashers, clothes washers and dryers
  • Turn off all unnecessary lights
  • Unplug unused items

Hot temperatures are expected to peak over the weekend, bringing a chance of record-setting heat Sunday and increased risk of fire danger to the Southland. The weather conditions have prompted the National Weather Service to issue excessive heat warnings for parts of Los Angeles, San Bernardino and Riverside counties until Monday evening.

Cal Fire said earlier this week that the number of fires and amount of land burned in 2021 has exceeded that of 2020 for the same time period.