Low clouds topping the deep marine layer were predicted to depart over San Diego County later Sunday morning, leaving sunny skies and seasonal weather Sunday afternoon, the National Weather Service said.
"For Memorial Day, our marine layer will begin to shrink as a weak trough aloft gives way to a ridge building over northern California," forecasters said. "As the ridge builds east, a weak low pressure will form over Baja, setting up a more moist, easterly flow with periods of high clouds and warmer conditions."
Onshore flow was expected to keep coastal and western valley areas near normal, but farther inland and across the deserts, it could be noticeably warmer, the NWS said.
High temperatures in coastal areas Sunday were expected to be 65-70 degrees with overnight lows of 53-58, the NWS said. Western valley highs will be 71-76 and 75-80 in the foothills with overnight lows of 51-56.
Mountain highs were expected to be 76-86 with overnight lows of 51-59. Highs in the deserts will be 98-103 with overnight lows of 67-75.
The weak upper-level trough over Southern California Sunday morning was forecast to slip slowly east Sunday, but a part of the trough will hang back to form a weak low-pressure center over the Baja Peninsula by Tuesday.
A weak easterly flow aloft over Southern California through midweek was expected to set up for warmer weather and more high clouds as moisture is drawn westward aloft.
At the same time, onshore flow will persist and maintain the marine layer over coastal and western valley areas, keeping those areas moderate as the deserts heat up, the NWS said.
The warmest days far inland were expected to be Wednesday through Friday, when daytime highs could be from 5-10 degrees above average.
A developing trough in the Pacific Northwest later in the week was predicted to increase onshore flow and begin a cooling trend into next week.
An incoming south swell was expected to bring elevated surf of 4-6 feet to south and southwest facing beaches Wednesday through Saturday, forecasters said. The increase in surf could create hazardous swimming conditions and an increased risk for strong rip currents.
