Returning onshore flow will spread cooling a higher humidity to inland San Diego County this weekend, with a return of coastal low clouds and fog tonight and Sunday morning, the National Weather Service said.
A Pacific storm system will move through Southern California late Sunday night through Monday night and bring occasional rain and snow in the mountains, with a slight chance of thunderstorms, forecasters said.
Dry but chilly weather will return Tuesday, with a gradual warming trend the second half of next week.
High temperatures along the coast Saturday were expected to be 61-66 degrees with overnight lows of 43-48, the NWS said. Valley highs will be 67-72 with overnight lows of 41-47.
Mountain highs were expected to be 60-67 with overnight lows of 36-45. Highs in the deserts will be around 73 with overnight lows of 42-52.
"A weak trough of low pressure will move through northern California and northern Nevada Saturday and help bring more onshore flow to Southern California, opening the door to low clouds and fog near the coast Saturday night," forecasters said. "The marine layer should deepen rapidly, so the stratus should make it into the valleys by Sunday morning, and Sunday will be rather cool and also increasingly breezy in the mountains and deserts."
The storm system will dig southward off the California coast Sunday and arrive in San Diego County late Sunday night, the NWS said.
"Right now, it looks like there could be three waves with the system which could prolong the steadier precipitation, resulting in a bit higher total precipitation amounts than previously thought, though maximum rainfall rates are staying about the same," forecasters said.
This will be a colder system with Gulf of Alaska origins, so the snow level should fall to 4,000 to 5,000 feet Monday morning.
"There is a slight chance of thunderstorms Monday into Monday night," forecasters said. "Some of these showers or thunderstorms could be briefly heavy, prompting concerns for the fresh burn scars. Snowfall could reach a foot in some mountain locations, mainly above 6,000 feet."
The storm system is expected to clear the area sometime on Tuesday, with showers lingering longest over San Diego County, possibly into early Tuesday morning, the NWS said.
While Tuesday will be quite chilly, warmer and dry weather is expected Wednesday into Thursday.
Another trough could move by to the north or northeast Thursday night into Friday and could bring some deepening of the marine layer or possibly even coastal drizzle.
At county beaches, a west-northwest swell is expected late Sunday into Monday, and will be followed by a slightly larger swell late Monday and Tuesday. These incoming swells will generate areas of high surf as early as Sunday, and lasting through early Wednesday.
Highest surf conditions are expected Monday afternoon through Tuesday, when local sets could reach 10 feet in southern San Diego County, forecasters said. Elsewhere, sets will generally range between 6-8 feet.
Additionally, there will be a slight chance of thunderstorms and lightning at the beaches on Monday.
A beach hazards statement remains in effect this weekend in anticipation of high surf, dangerous rip currents and the possibility of lightning, the NWS said.