"Consumers are urged to conserve electricity especially during the late afternoon when air conditioners typically are at peak use," the California ISO said in a statement. "Consumers can help avoid power interruptions by turning off all unnecessary lights, using major appliances before 2 p.m. and after 9 p.m. and setting air conditioners to 78 degrees or higher."
The alert comes as temperatures hit the triple-digits in the Valleys and Inland Empire before noon.
Most of the Southland will remain under an excessive heat warning until Friday, and many Southern California residents said their plans to beat the heat consisted of staying indoors.
MORE: Scorching temperatures linger across Southland on Tuesday
To add to the discomfort, the South Coast Air Quality Management District issued a notice that air quality will be unhealthy for sensitive people in Santa Clarita, east and west San Gabriel Valley and areas in Pomona.
"Stay inside," said Santa Clarita resident Tari Spitalni. "I think it's just a matter of doing things early or late and really just keeping yourself well-hydrated, as well as staying out of the sun."
It may be difficult to endure the scorching heat, but the ISO noted that the power grid can become strained amid high air-conditioner use in hot weather.
It said the peak use expected Tuesday is 48,000 megawatts, which would be the highest demand this year, and urged such conservation measures as setting thermostats at 78 or higher, turning off unnecessary lights and appliances, and saving major-appliance use for the morning or late evening.
City News Service contributed to this report.