Flash flood watch for Antelope Valley, mountains, as deep marine layer covers Southern California

A low-pressure system drew a deep marine layer over Southern California on Sunday, with a flash flood watch for the Antelope Valley and some Los Angeles County mountains, the National Weather Service said.

Monday’s forecast was for drier conditions. The National Weather Service projected mostly cloudy conditions in downtown Los Angeles in the morning, followed by sunny conditions in the afternoon. The high should reach 69 degrees Monday followed by highs later in the week in the 70s.

Highs Monday should reach 74 in Santa Ana as clouds gradually clear, while the temperature should reach 83 degrees at San Bernardino International Airport as that area can expect mostly sunny conditions.

On Sunday, cold air aloft was contributing to the unstable conditions, particularly in the Cuyuma and Antelope valleys, the NWS Los Angeles/Oxnard office said.

The flash flood watch Sunday night excluded the Santa Monica Mountains but included other mountains in Los Angeles, Santa Barbara and Ventura counties including the areas of San Marcos Pass, San Rafael Wilderness Area, Dick Smith Wilderness Area, Lockwood Valley and Mount Pinos.

The watch extended into the mountains west of Wrightwood and north and northeast of Burbank.

Flooding dangers were possible especially in higher terrain and the back country of the mountains, the NWS said.

But most areas in Orange County and the San Bernardino and Riverside areas of the Inland Empire were free of watches, warnings and advisories Sunday night.