California’s power grid operator is asking residents to conserve electricity Thursday evening, when a surge of air conditioning use amid sweltering temperatures could overtax the state’s power supply.

The statewide Flex Alert, a public appeal for power conservation, will start at 3 p.m. Thursday and last until 10 p.m., the California Independent System Operator said.

Temperatures in the mid-90s to low 100s are expected Thursday in the North Bay and extreme heat is also forecast for parts of Southern California.

If power levels drop too low, the operator may issue rolling power outages, as was done in mid-August, when record-breaking heat drove up energy use.

Californians are urged to turn off lights, unplug unused devices and avoid using large appliances during the Flex Alert period, the power operator said.