Strengthening onshore flow over San Diego County Saturday was expected to deepen the marine layer for progressively cooler weather into next week, the National Weather Service said.
Some patchy drizzle could break out Sunday night as a marine layer spreads fog and clouds well up the coastal mountain slopes, forecasters said.
A slow-moving storm system was predicted to increase the chances for rain and mountain snow from late Tuesday through Wednesday and keep daytime temperatures well below normal, the NWS said.
Cool weather and showers may linger through Friday night before dry and slightly warmer weather returns next weekend.
Coastal area high temperatures Saturday were expected to be around 66 degrees with overnight lows of 46-52, the NWS said. Inland valley highs will be 66-71 with overnight lows of 40-48.
Mountain highs were expected to be 61-69 with overnight lows of 33-43. Desert highs will be 82-87 with overnight lows of 48-56.
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The large trough was expected to slowly dip southward toward Southern California midway through next week.
"If you think the weekend will be a bit cool, get ready for the middle of the week," forecasters said. "Temperatures are not looking that warm, with highs struggling to reach 60 for many areas west of the mountains and only 30s and 40s for the mountains."
Clouds and showers will start to overspread the region as early as Tuesday afternoon from west to east, the NWS said.
"San Diego County looks to be the hardest hit, with much of the coast and valleys looking to get close to one inch of rain in total," forecasters said. "Snow levels will start out a bit over 4,000 feet on Tuesday and sink to around 3,500 feet early on Wednesday after going back up to 4,000 feet later on Wednesday into Thursday."
Areas near 6,000 feet may see 4 inches of storm total snow or more, with some areas above 8,000 feet seeing 8 inches or more, the NWS said.
At area beaches, an increased west swell will result in elevated surf and a high rip current risk at the beaches Saturday into early Sunday. Surf will mainly range from 3-5 feet, with sets to 6 feet possible in southern San Diego County.
