SAN FRANCISCO (KRON) — As an unprecedented September heat wave that’s engulfed the Bay Area in record heat persists for at least another day, the California Independent Operator has issued a Flex Alert for Friday.

The Flex Alert for Friday takes effect at 4 p.m. and will last until 9 p.m. It is the 10th consecutive day that Cal ISO issued a Flex Alert.

What is a Flex Alert?

According to the CAISO website, a Flex Alert is “a call for consumers to voluntarily conserve electricity when there is a predicted shortage of energy supply, especially if the grid operator needs to dip into reserves to cover demand. When consumers reduce electricity use at critical times, it can prevent more dire emergency measures, including possible power outages.”

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Voluntary conservation has helped reduce the unprecedented strain on the state’s grid during this week’s prolonged heat wave. While CAISO and Cal OES officials have not yet issued statewide rolling outages this week, communication issues led to several Northern California cities mistakenly implementing planned outages on Tuesday, despite not being called on to do so.

While there have been widespread outages this week that have at times left thousands without power, those have been mainly caused by excessive heat causing equipment to malfunction.

Thursday’s forecast calls for one more day of excessive heat before a return to relatively normal temperatures begins Friday.