FXUS66 KSGX 141637 AFDSGX Area Forecast Discussion National Weather Service San Diego CA 937 AM PDT Mon Oct 14 2024 .SYNOPSIS... There will be slight day-to-day differences in high temperatures through Wednesday. The marine layer will deepen with night and morning coastal low clouds spreading inland across much of the valleys for Tuesday and Wednesday. For late in the week through next weekend, a low pressure system from the northwest will move into the area, then stall over the weekend as a closed upper level low pressure system develops somewhere over the southwest states. There could be some light precipitation centered around Thursday with greater spread with temperatures and winds for next weekend dependent on the uncertain placement of the low pressure system over the southwest states. && .DISCUSSION...FOR EXTREME SOUTHWESTERN CALIFORNIA INCLUDING ORANGE... SAN DIEGO...WESTERN RIVERSIDE AND SOUTHWESTERN SAN BERNARDINO COUNTIES... .Morning Update... Low clouds have moved to many inland valleys, including portions of the Inland Empire where dense fog has been reported. Our forecast remains on track for clouds to partially clear to the coast by early afternoon for many. The marine layer will become slightly deeper by tonight, where most areas west of the mountains will see another round of cloudy conditions. As stated yesterday, patchy drizzle will be possible in these areas with minimal accumulation. We continue to watch our next weather system poised to impact the region later this week. Santa Ana winds are beginning to look increasingly likely with a chance of light precip, but strength and timing of these details remains uncertain as the track of the low pressure system is still in flux. Temperatures continue to look on the cooler side with lows getting into the 20s and 30s for higher elevations and 40s and 50s for lower elevations. Previous Discussion (439 AM Monday)... .SHORT TERM (Today through Wednesday)... A weak upper level low pressure system centered over Nevada will move southward into Arizona on Tuesday, then move east on Wednesday as a low pressure system begins to move inland along the West Coast. High temperatures for the coast and valleys will remain below average with the deserts around 5 degrees above average. The local NAM-bounded workstation WRF shows deepening of the marine layer to 2500 to 3000 feet for Tuesday and Wednesday with night and morning coastal low clouds spreading inland across much of the valleys. && .LONG TERM (Thursday through Sunday)... A low pressure system from the northwest will continue to move inland into the western states for Thursday and Friday with a closed upper level pressure system developing somewhere over the southwest states on Saturday and lingering into Sunday. Some light precipitation is possible from the coastal waters to the mountains centered some time around Thursday. The spread in the NBM high temperature guidance is much larger for Friday through Sunday with a general slow warming trend. Cluster analysis shows little overlap of GFS ensemble members with those of the European and Canadian models with greater overlap of the ensemble members of the European and Canadian models. The GFS members are more amplified with the upper low with those of the European and Canadian models less amplified. ECMWF ensemble output for Campo has trended weaker with the winds for the weekend with fewer members with stronger winds and more with weaker winds and the timing of potentially stronger winds spread out across Saturday and Sunday versus earlier runs which were centered during the day on Saturday. && .AVIATION... 141635Z...Coast/Valleys...Low clouds with bases 1500-2000 ft MSL and tops to 2500 ft MSL cover much of the region west of the mtns at this hour. Clouds are obscuring higher terrain, with VIS restrictions where clouds and terrain intersect. Clearing from inland to the coast likely to be slow (17Z-20Z) with only partial clearing at the immediate coast. Low clouds will spread rapidly inland after 01Z into early Tuesday. Bases/tops/VIS will be a little higher and clouds will fill most of the coastal basin by 12Z Tuesday. Mountains/Deserts...Mostly clear skies with unrestricted VIS through tonight. && .MARINE...No hazardous marine conditions are expected through Friday. && .BEACHES... Surf of 3-5 feet with local sets to 6 feet with strong rip currents today due to a combination of west and south swells each around 3 feet/15-16 seconds. Surf will decrease on Tuesday. && .SKYWARN... Skywarn activation is not requested. However weather spotters are encouraged to report significant weather conditions. && .SGX WATCHES/WARNINGS/ADVISORIES... CA...None. PZ...None. && $$ PUBLIC...APR/17 AVIATION/MARINE...PG