Morning clouds
A satellite view of clouds over Southern California on Tuesday morning. Courtesy National Weather Service

A weak low-pressure system off the California coast was expected to move inland across Southern California Tuesday evening and Wednesday, the National Weather Service said.

A larger low-pressure system to the north on Thursday could bring stronger onshore flow and spread cooling inland with Thursday high temperatures as much as 20 degrees below average for the mountains and inland valleys, forecasters said.

While the marine layer was around 4,000 feet deep early Tuesday, the strength of the marine inversion was weaker and coverage of coastal low clouds patchier with the most widespread coverage across the valleys in San Diego County, the weather service said.

Greater coverage of coastal low clouds was expected for Tuesday night into Wednesday morning and for Wednesday night into Thursday with the most likely time for drizzle late Wednesday night into Thursday morning.

Along the coast Tuesday, it was expected to be partly cloudy and high temperatures from 70 to 73 degrees. Inland areas were expected to be partly cloudy and highs at 74. It should be mostly sunny in the mountains with highs from 74 to 84. The deserts were predicted to be mostly sunny with highs around 95.

High pressure to the south may bring warming for the weekend with tropical moisture from the southwest bringing mid and high clouds for Friday and Saturday, forecasters said.