A ridge of high pressure will continue to provide warm weather through Tuesday with coastal low clouds and fog at times. A trough of low pressure off the coast will influence our weather starting Wednesday and continue through the weekend. This will bring cooling, a deeper marine layer and breezy west winds across the mountains and deserts. A few showers could occur around next Sunday.
For extreme southwestern California including Orange, San Diego, western Riverside and southwestern San Bernardino counties,
Update,
Low clouds came surging onto land, especially in San Diego County, late this afternoon when a coastal eddy had formed, but with the later disappearance of the eddy, they have retreated back to the coastal waters, except in northern Orange County. San Clemente Island's METAR had very low clouds 250-350 feet above sea level, indicating that the marine layer had become quite shallow out there. Confidence is low on timing or location of fog tonight but guidance suggests some dense fog forming near the coast at least late tonight and early Tuesday morning. Otherwise, Thermal and Indio hit 100 today, the first 100 degrees readings in California of 2025, and a few more stations should hit 100 on Tuesday. Most of the guidance is falling a bit short of 100 at PSP for Tuesday, but given the airport usually exceeds guidance by a couple degrees, there is about a 50% chance they will reach 100. Temperatures within about 10 miles of the coast are rather low confidence Tuesday as they will depend on the extent of marine layer stratus/fog in the morning. Otherwise, the cooling trend Wednesday, even in the deserts, looks on track.
From previous discussion,
A 1025mb area of high pressure just offshore has led to a warm day out there with temperatures reaching well into the 80s and near 90s in the Inland Empire and 60s/70s across much of the mountains. This with light offshore winds will help some spots close in on daily record highs today for places like Ramona and Riverside. Similar temperatures will occur on Tuesday, potentially a couple degrees warmer away from the coast. If you must be outside during this heat, make sure to take breaks and drink plenty of water. This area of high pressure has helped to squish the marine layer, keeping low clouds and foggy conditions along the immediate coast. This will be intermittent this afternoon, expanding in greater coverage this evening and overnight. Some of this fog may be under one mile at times, so stay safe if traveling.
A trough of low pressure will move into the West Coast by Wednesday. This will significantly cool areas west of the mountains around 10 to 15 degrees as the deserts remain in the 90s. The pressure gradient will tighten as the system pushes into southwestern British Columbia. As it does, so further cooling for all of Southern California will occur into Friday. This system will also bring elevated winds to the mountains and deserts. Chances are moderate that gusts over 40 mph occur across the mountain desert slopes Thursday and Friday. The marine layer will also be much deeper during this time, so expect night and morning low clouds for much of the coastal basin. An area of moisture is shown in some models offshore by the end of the week. Most model ensembles are leaning dry, but a small chance for showers may occur by Sunday, especially areas north of San Diego County.
250315z, Coast/Valleys, Low clouds have momentarily retreated offshore this evening. Low clouds and fog are expected to come back ashore after 06Z, moving up to 10 miles inland overnight. Bases may start at 400-700 ft MSL but will lower overnight to 200-400 ft MSL with vis 0-3 SM, lowest on coastal mesas/highlands. Clouds/fog scatter out of most areas 16-18Z Tuesday, but will linger along beaches. Low clouds will then move inland again after 01Z Wed with higher bases 400-800 ft MSL that will continue to rise overnight, moving further into inland valleys as it does.
Otherwise, Mostly clear skies except for increasing high clouds AOA 20,000 ft MSL tonight into Tuesday.
Areas of dense fog with visibility at or below 1 NM are possible through Tuesday morning. For details, check the Marine Weather Statement. On Thursday and Friday, winds could gust near 20-25 mph with a 50-75% chance of Small Craft conditions in the outer coastal waters. Otherwise, no hazardous marine conditions are expected.
Ca, None. PZ, None.
