Slight cooling today along the coast, with more widespread cooling and Monday. Patchy dense fog is possible over the coastal waters and along the immediate coast Sunday night into Monday morning and again Monday night into Tuesday morning. Warmer Tuesday through Thursday with additional periods of Santa Ana winds, followed by cooling and a return of onshore flow Friday and Saturday.
For extreme southwestern California including Orange, San Diego, western Riverside and southwestern San Bernardino counties,
Skies remain clear under weak offshore flow this morning. Water vapor imagery shows the upper ridge shifting eastward as a trough approaches the Pac NW. Weak troughing is forecast to develop today into Monday across So Cal as the ridge breaks down, bringing minor cooling and a return of weak onshore flow. Most of the cooling will occur along the coastal areas today, while inland areas remain anywhere from 10-15 degrees above normal. More widespread cooling takes place on Monday, with highs around 5-10 degrees above normal. With the return of onshore flow comes the potential for the marine layer to redevelop, bringing fog to the coastal waters and coastal areas. The HREF currently has a 50-70% chance of low clouds over the coastal waters and locally into the coastal areas by Monday morning. Low clouds and fog will likely hang on for Monday night into Tuesday morning.
An upper level high rebuilds over CA/NV Tuesday into Wednesday. Surface pressure gradients turn back offshore on Tuesday, producing weak Santa Ana winds. Winds strengthen Wednesday when there is around a 30% chance of a moderate Santa Ana event and a 60% chance of a weak to moderate event. Temperatures begin to climb again, reaching as much as 15-20 degrees above normal west of the mountains by Wednesday, and a 70-90% chance of high temperatures exceeding 85F for the valleys and inland coastal areas per the NBM. The upper high begins to weaken and shift east on Thursday with continuing weak to moderate Santa Ana winds, allowing for minor cooling.
Uncertainty grows later in the week as ensemble solutions begin to diverge on the evolution of the upper level pattern, particularly with the progression of an upper low moving into the West Coast. A cooling trend is a certainty, but how much cooling we'll see will depend on how the low tracks. A few members of each of the global ensembles are producing light precipitation with this low over the weekend, but not enough to introduce a slight chance into the forecast. The alternative to any precipitation would be another round of offshore flow developing by Sunday.
011000, Widespread VFR conditions expected through late this evening with increasing high clouds AOA 20k ft beginning late morning. Local gusts 15-20 kts expected through 00Z in the mountain passes, foothills and adjacent valleys. Patchy low clouds/FG will develop late this evening along the immediate coast after 06Z, with a 60% chance for CIGs at KSAN by 09Z and 25% chance KCRQ/KSNA by 12Z. 30-40% chance for VIS less than 1/2 SM, with CIGs 100-400 ft MSL. Low clouds/FG clearing to beaches Mon 15-17Z.
Patchy fog likely to develop over the coastal waters this evening through late Monday morning, with areas of visibility under 1 SM possible. Otherwise, no hazardous marine conditions are expected through Thursday.
Northwest swell increases to 3-5 feet with a period of 15-17 seconds early Monday, leading to breaking wave heights of 5-8 feet with sets to 9 feet on west facing beaches in San Diego County, and 4-6 feet for west-facing beaches in Orange County Monday through Tuesday morning.
High tides around 6-6.6 feet Monday and Tuesday mornings, combined with the larger surf, will result in minor tidal overflow in Orange County through Monday evening, and minor flooding for low-lying beach lots and walkways in San Diego County through Tuesday morning.
Ca, Coastal Flood Advisory from 4 AM Monday to 10 AM PST Tuesday for San Diego County Coastal Areas.
High Surf Advisory from 4 AM Monday to 10 AM PST Tuesday for San Diego County Coastal Areas.
Beach Hazards Statement from late tonight through Monday evening for Orange County Coastal Areas.
PZ, None.
