Areas of dense fog on the coastal mesas and western valleys again tonight into Monday morning. Well above normal high temperatures through Thursday, with periods of weak offshore flow through Tuesday. Gradual cooling with more widespread night and morning low clouds and fog for Friday into next weekend.
For extreme southwestern California including Orange, San Diego, western Riverside and southwestern San Bernardino counties,
Mostly clear this afternoon with a few high clouds and areas of low clouds persisting at the immediate coast. Temperatures are generally lower but within a few degrees of what they were at this time yesterday. Inland high temperatures will be well above seasonal averages but the marine layer presence will keep temperatures near the coast closer to normal.
This pattern of low clouds and fog will likely repeat for tonight into Monday morning even as the upper level trough moves eastward into AZ, although the low clouds may be a little higher and low visibility not as widespread. After the upper trough moves east, high pressure aloft begins to build in from the west and offshore flow develops on Monday, with winds gusting to around 30 mph below the passes and canyons. Weak offshore flow under high pressure aloft will persist into Tuesday and mitigate or nullify the influence of the marine layer so that low clouds and fog are unlikely to return for Mon night/Tue morning or Tue night/Wed morning. It will also bring drier and warmer conditions into the coastal areas, resulting in daytime high temperatures on Tuesday as much as 10 degrees above seasonal averages in the coastal areas, and up to 20 degrees above average in the far inland valleys. Tuesday is likely to be the warmest day overall, with high temperatures reaching the 80s in the inland valleys and lower deserts.
Onshore flow returns on Wednesday as a shortwave trough moves inland to the north and the upper level ridge weakens and flattens out. This could bring some cooling to the coastal areas and far western portions of the inland valleys, and potentially a return of low clouds and fog to the coastal areas Wed night. However, this is a fast-moving trough and offshore flow quickly returns on Thursday as a sfc high follows the departing trough into the Great Basin. The offshore winds will bring drier and warmer conditions but are unlikely to be strong enough to produce any other impacts.
As we approach next weekend, a more vigorous trough will displace the upper high to the south, establishing a high-zonal pattern over CONUS. This pattern is expected to bring a weak atmospheric river to central and northern CA next weekend but SoCal will likely remain dry but cooler with more of a marine layer presence as onshore flow returns. Temperatures for next Sat and Sun will range from near normal at the coast to about 10 degrees above normal in parts of the inland valleys.
142130z, Coast/Valleys, Low clouds, now based around 900-1100ft MSL have finally cleared out of the coastal areas by 21z this afternoon, though lingering clouds along the beaches and within a mile of the coast remain possible through the afternoon. Outside of the clouds, trapped moisture and particles within portions of the coast and inland valleys are leading to HZ this afternoon, with pockets of 6SM and locally near 5SM VIS possible. Low clouds will push back inland again as early as 00-02z this evening. Cloud bases initially near 700-1000ft MSL this evening should settle to 400-900ft MSL by 06z. VIS down to 0-3SM for inland areas as low clouds/fog move in with VIS for coastal areas down to 2- 5SM. Clouds/fog expected to clear a bit earlier Monday morning, around 17-19z.
Mountains/Deserts, Clear skies and VFR conditions expected through the Monday afternoon.
Low clouds have lifted over the waters this afternoon, but should settle back down this evening, with areas of light fog bringing visibilities of 2-5 nautical miles. Otherwise, no hazardous marine conditions are expected through Thursday.
Ca, None. PZ, None.
