The overnight temperature in Palmdale dipped to 19 degrees, breaking the record of 25 set in 1954, Bruce Rockwell, a meteorologist in Oxnard, said this morning.
Alpine in San Diego County reported a reading of 31 degrees, breaking a record of 33 set in 1991.
"We do tend to get cold this time of year," Rockwell said.
Long nights, clear skies, the sun at a low angle and a lack of wind and moisture are "the ingredients for the cold," he said.
Freeze or frost warnings were in effect for parts of Southern California overnight, and may be posted again tonight.
A frost warning means that people should protect tropical and other sensitive plants, such as hibiscus, by covering them with plastic, said Stan Wasowski, a forecaster with the National Weather Service in San Diego.