Warmer conditions expected through Monday with periods of weak offshore flow. Locally dense fog is possible again tonight and Sunday night into Monday morning over higher coastal terrain. Cooler conditions expected by the middle to end of next week. A windy and wet pattern is expected to develop for the end of next week.
For extreme southwestern California including Orange, San Diego, western Riverside and southwestern San Bernardino counties,
Evening update, Low clouds have already filled in across much of the Orange County coastal plain, but remains patchier over San Diego County where east winds are beginning to strengthen, though said winds are not making it all the way to the coast. Clouds should fill in over the San Diego County coastal areas by late tonight, eventually becoming squashed down and pushed out to sea Sunday morning as offshore winds continue to strengthen. As the marine layer lowers, pockets of dense fog are possible again, mainly across the coastal mesas and other higher coastal terrain. Otherwise for tonight, clear skies with winds gustying 30-45 mph below the passes/canyons and along the coastal slopes and foothills of the mountains.
Previous discussion, Strengthening high pressure aloft and periods of offshore flow will bring warming conditions across the area. The peak of the heat is expected for Sunday and Monday when highs will be as much as 12-17 degrees above seasonal averages. Areas of minor to moderate HeatRisk are expected, with the highest HeatRisk expected in the western valleys. Weak to locally moderate northeast to east winds are expected on the coastal slopes of the mountains and through passes and canyons. Strongest winds are expected on Sunday and Monday when gusts of 30-45 mph are expected in the favored locations.
For the middle of next week, guidance is becoming more in line. There is increased confidence in the cooling trend starting for areas west of the mountains on Tuesday, with cooling spreading further inland Wednesday. We also have much higher confidence that Wednesday will stay dry. Chances of precipitation enter the forecast as early as Thursday north of San Diego county, with chances increasing and spreading south and east into Friday. Ensemble members of both the ECMWF and GFS are beginning to show the highest chances of precipitation being sometime on Friday. There does remain considerable uncertainty in amounts of precipitation with some members showing much wetter solutions than others. This likely has to do with lingering uncertainty in the timing of the low pressure system and how far south it will dig. This uncertainty continues to impact other factors of the forecast including the temperature, wind, and chances of snow. Current forecast for the end of the week closely follows the NBM with cooler and cloudier conditions and chances of precipitation starting as early and Thursday and continuing through next Saturday.
090400z, Coasts, Patchy low clouds 400-800 ft MSL have formed over Orange County and northern San Diego County coastal areas with VIS reductions over coastal areas 2-6 SM in BR, and dense FG over elevated coastal terrain. Low clouds/FG will become more widespread overnight if still somewhat patchy, spreading inland 5-10 miles. Expecting bases to lower to 200-600 ft MSL overnight with areas of dense FG down to sea level after 09Z (including KSAN). Scattering to the coastline again 14-17Z Sun. Patchy low clouds/FG with similar bases to form along immediate coast after about 03Z Mon.
Valleys/Mountains/Deserts, Clear skies and VFR conditions through the period. Localized east to northeast winds picking up after 12Z Sun downwind of passes through the Inland Empire and along coastal slopes of the mountains leading into the foothills. Intermittent gusts 25-35 mph in these areas.
Low clouds over coastal waters today will slowly lower toward sea level starting late this evening. Visibility is expected to drop below 1 SM in patchy areas of dense fog early Sunday morning. Visibility expected to improve mid to late morning.
Ca, None. PZ, None.
