High temperatures for the date were recorded in Palm Springs (119 degrees) and Palmdale (107), breaking records that were set in the 1960s, according to the National Weather Service.
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Idyllwild saw a record-tying temperature of 98 degrees, last seen in that Riverside County community in 1961.
The latest Southern California forecast is here.
Latest weather with Tony Cabrera
The heat wave is expected to continue all week, potentially getting even hotter on Wednesday.
The California Independent System Operator says it should have enough electricity to meet demand and avert outages. But disruptions such as wildfires that burn transmission lines or other unexpected problems could lead to the first "Flex Alert" of the year.
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Officials say that if an alert is called, people would be asked to voluntarily cut electricity use from 4 to 9 p.m. Wednesday and Thursday.
"More records are at risk tomorrow," the National Weather Service warned.
Southern Californians are advised to take precautions during the heat wave. Stay indoors and seek cooling centers if you don't have air conditioning at home. Keep hydrated. Keep an eye on pets and children and don't leave them in vehicles unattended for any amount of time.
Tips for staying safe during a heat wave as the temperature rises
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Tips for staying safe during a heat wave as the temperature rises
A red flag warning is also in place as the hot weather and dry conditions can produce a rapid spread of fire.
The Associated Press contributed to this report.