Although no weather advisories were in effect, National Weather Service meteorologists said the thunderstorms may drop brief but heavy rainfall and could produce occasional cloud-to-ground lightning Tuesday afternoon and evening.
Forecasters said the valleys and deserts would have an about 20 percent chance for measurable precipitation in the afternoon through Wednesday, and the mountains had a 20 percent chance of measurable rain through Thursday.
"High pressure over the Great Basin and low pressure off the California and Baja coasts will continue to direct a flow of mid and high level monsoonal moisture across Southern California for much of the week into early next week,'' according to the weather service. "This will support a chance of thunderstorms through Thursday, mainly near the mountains and portions of the deserts during the afternoon hours.''
The precipitation is expected to move northwest out of the region, but may produce a few sprinkles west of the mountains as it dissipates, according to the weather service.
Forecasters predicted high temperatures throughout the county would peak Tuesday, then cool to near average for Friday through early next week.
Highs Tuesaday are expected to range from 72 to 77 degrees along the coast, 84 to 89 in the western valleys, 90 to 95 degrees near the foothills, 88 to 95 degrees in the mountains and 105 to 110 degrees in the deserts.
High temperatures are expected to fall a few degrees by Friday. Fridays highs will range from 71 to 76 near the beaches, 75 to 80 in the western valleys, 80 to 85 degrees near the foothills, 81 to 88 degrees in the mountains and 103 to 108 in the deserts.