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Californians are being urged to conserve electricity as blistering heat strains the state’s electric grid.

A statewide Flex Alert was issued for Thursday evening, from 5 p.m. to 10 p.m., to avoid power disruptions and rolling blackouts, according to the California Independent System Operator, which runs most of the state’s electric grid.

Flex Alerts are a call to consumers to voluntarily conserve energy when demand for power could outstrip supply, which generally occurs during heat waves when electrical demand is high. The ISO recommends setting the thermostat to 78 degrees or higher, avoiding use of major appliances, turning off unnecessary lights, using fans to cool your home and unplugging unused items.

Conservation is important in the evening as it’s “the most critical time for the power grid, because solar production is ramping down, while electricity demand can remain high during these extreme heat events,” according to the ISO.

Officials with the system operator said in a new briefing Wednesday afternoon that residents can pre-cool their homes ahead of the 5 p.m. hour and then keep curtains drawn to keep the cold air in. They also suggested charging phones and other devices ahead of the Flex Alert period.

“We will be relying on Californians to be partners in protecting grid reliability in this heat event and throughout the summer, when needed,” the ISO said in their daily bulletin Wednesday.

The ISO initially deleted a tweet announcing Thursday’s Flex Alert but the notice remains listed under “current active notices” on their website.

During Wednesday’s briefing, ISO officials said they are cautiously optimistic that the state is in a better position than it was last year, when rolling blackouts were issued across California. There are a number of steps the state has taken, including acquiring an additional 3,500 megawatts of capacity ahead of a likely scorching summer.

“Does that mean we are in the clear? Not necessarily,” Elliot Mainzer, president and CEO of the ISO, told state lawmakers last month during an oversight hearing. “The most significant risk factor for grid reliability remains extreme heat, particularly heat that spreads across the wider western United States. And it continues to get hotter every year.”

Rolling blackouts have become a method for utility companies in the state to intentionally turn off the power when it gets too windy in dry summer months to prevent power lines from toppling and starting wildfires. Such blackouts in August 2020 were the first in nearly two decades caused by an energy shortage.

This week’s sweltering heat in the region stretched from southeast California across Arizona and Nevada and into New Mexico. Palmdale, in the Mojave Desert, hit 107 degrees Wednesday, breaking a record of 105 that was set in 1966.

An excessive-heat warning is also in effect in the mountains of Ventura and Los Angeles counties, excluding the Santa Monica range, until 9 p.m. Friday.

Five Flex Alerts were issued in 2020, in comparison to one in 2019 and two in 2018, data show.