Fair and warm weather with variable high clouds through the end of the week, along with patchy coastal low clouds and fog Wednesday and Thursday mornings. Brisk westerly winds will develop for late Wednesday mainly in the mountains and high deserts. Cooler with increasing clouds for early next week.
For extreme southwestern California including Orange, San Diego, western Riverside and southwestern San Bernardino counties,
Evening update, Scattered high clouds continue to move across the region this evening atop the upper level ridge of high pressure to our southwest. Surface pressure gradients have turned back onshore, currently around 3.3 mb SAN-DAG. Dew points have increased to the upper 50s along the immediate coast, but drier air only a few miles inland will probably drain towards the coast as the land breeze/drainage flow develops overnight. The 00Z HREF has around a 40-50% of low clouds along parts of the coast early Wednesday morning. Low clouds/fog are more likely to develop Wednesday night into Thursday morning as onshore flow strengthens. No changes to the forecast this evening as warm and dry weather prevails.
Previous discussion, The ridge of high pressure will continue to dominate our weather into the weekend and the warming trend will continue through Friday. High temperatures today are expected to be in the upper 60s to mid 70s near the coast, in the upper 70s to low 80s in the inland valleys, the 50s to 60s in the mtns, the upper 70s in the high deserts and in the upper 80s in the low deserts. These temps are as much as 13-17 degrees above seasonal averages in the valleys, mtns and deserts. Friday will likely be the warmest day, with temperatures as much as 20 degrees above seasonal averages in the valleys, mtns and deserts. Temperatures on Saturday lower slightly as the upper ridge weakens but will remain 15-20 degrees above seasonal averages.
At the surface, onshore flow peaks Wednesday with gusty west winds mainly in the high deserts and the mtns. Onshore flow will continue through Thursday before turning offshore briefly on Friday. The onshore flow will likely bring a return of coastal marine layer clouds/fog for tonight/Wed morning and again for Wed night/Thu morning. High-resolution ensemble models show a 30-40 percent chance of patchy clouds/fog for tonight/Wed morning and a 40-60 percent chance of more widespread low clouds/fog Wed night/Thu morning. On Friday, weak offshore flow will likely disrupt the marine layer.
For Sunday through next Tuesday, numerical models are coming into better agreement with respect to the evolution of the synoptic pattern. At this time, we can say with reasonable confidence that a low pressure system from the northwest will move over or close to SoCal. It will likely bring increasing clouds and cooler conditions. Temperatures on Monday will lower to about 5-9 degrees above seasonal averages. This system could also bring some precipitation but at this time that seems unlikely as only about 25 percent of ensemble members show any chances for precip.
250400z, VFR conditions expected through the TAF period. Mostly clear skies with high clouds AOA 10,000 ft MSL. Low confidence (20- 30% chance) for patchy fog to develop over the waters off the coast. Even if fog should develop, only a 10-20% chance for it to impact TAF sites KSAN/KSNA after 10z tonight with less than 1SM vis. Patchy fog scatter out 16-18Z. Low confidence for very patchy fog to develop offshore again, around 01-03z Thu.
No hazardous marine conditions expected through Sunday.
Ca, None. PZ, None.
