398 FXUS66 KSGX 141730 AFDSGX Area Forecast Discussion National Weather Service San Diego CA 930 AM PST Thu Dec 14 2023 .SYNOPSIS... Periods of gusty east to northeast Santa Ana winds with dry and warm conditions through Saturday. Onshore flow will return by Sunday afternoon. Increasing cloud coverage for the end of this week into next week. Chances of precipitation across much of the area next week. && .DISCUSSION...FOR EXTREME SOUTHWESTERN CALIFORNIA INCLUDING ORANGE... SAN DIEGO...WESTERN RIVERSIDE AND SOUTHWESTERN SAN BERNARDINO COUNTIES... Key Points: *Gusty Santa Ana winds, with dry and warm conditions through Saturday. *Chances of precipitation each day next week. *Low confidence in details of upcoming precipitation next week. Visible satellite imagery at 9 AM was showing mostly clear skies with a few patches of fog clearing along the LA/Orange County line and high clouds streaming to the southeast across the area. Wind gusts this morning have been mostly confined to the mountain foothills and below passes. Isolated wind gusts of 35 to 40 mph have occurred since midnight, with the strongest at Pleasants Peak. The east to northeast winds are expected to peak in strength again late tonight into Friday. Strongest gusts will be 35 to 45 mph in the San Diego and Riverside county mountains, foothills, and below passes, impacting the I-10 and I-8. Winds will weaken into Saturday with just a few isolated gusts to 40 mph expected in wind prone locations. By Sunday, Santa Ana winds will have weakened substantially and winds will transition back to onshore by the afternoon. In previous iterations of the forecast, guidance was indicating rainfall could start as early as Sunday afternoon but recent runs of the guidance have indicated a delay in the onset of precipitation. Both the GFS and ECMWF have delayed the arrival of the weak IVT plume that was forecast to reach Southern California by Sunday evening. Latest guidance of the ECMWF and GFS are now showing a weaker, more localized sliver of IVT now reaching portions of Southern California Monday afternoon. When it comes to ensemble guidance, only a couple individual members of the GFS and ECMWF are showing light precipitation Sunday afternoon and evening. Both global models are showing more support for the precipitation to begin sometime Monday. Slight chances of precipitation remain for Sunday evening, but due to the substantial dry layer and the drier trend in the models, measurable precipitation looks less likely for the end of the weekend and more likely for early next week. There is higher confidence that the incoming system will bring widespread high cloud coverage for the weekend into next week. After the short-wave passes early next week, global models show a closed low digging south from the Gulf of Alaska. Global guidance continues to show deviations in track and timing of the mid to end of next week system. At this point in time, it is tricky to pin-point when precipitation is most likely, especially for the middle to end of the week. Given the amount of available moisture that should be in the atmosphere there are chances of precipitation in the forecast each day through Thursday. There is the potential for a significant amount of precipitation from this second system but there is still significant spread in ensemble members for amounts on both global models. Current guidance is indicating the bulk of the precipitation will fall sometime Thursday and/or Friday. As far as temperatures go for the forecast period, highs today are expected to be 3 to 7 degrees above average, with increasing temperatures into Saturday. For Friday and Saturday, high temperatures are expected to be 7 to 15 degrees above average west of the mountains. In the deserts, high temperatures are expected to peak on Saturday at 6 to 10 degrees above average. With the transition to onshore flow Sunday, areas west of the mountains will begin to see some cooling, although highs will still be above average for this time of year. Cooling will spread inland to the deserts for Monday. Widespread cooling is expected to continue for much of next week. && .AVIATION... 141625Z...FEW-SCT AOA 25,000 FT MSL through tonight. Mountains/Coastal Slopes...Breezy N-NE winds with sfc gusts 20-30 kt and MOD up/downdrafts and LLWS over/W of mtns into Saturday. && .MARINE... No marine weather hazards are expected through Saturday. Periods of showers and larger swells Sunday through Monday. && .FIRE WEATHER... East to northeast winds will continue into Sunday morning mainly in foothills and portions of adjacent valleys. Winds will peak in strength Friday, with highest gusts 35-45 mph. Weaker winds expected Saturday but a few local gusts to 40 mph are possible in wind prone locations. Humidity will drop to around 15-20% each afternoon through Saturday except near the coast. Overnight humidity recovery will be poor in the breezy foothills. It will be warmer each day through Saturday, with high temperatures 7-14 degrees above average west of the mountains. Onshore flow will return Sunday afternoon, increasing humidity and rain chances into Monday. && .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/FIRE WEATHER...CO AVIATION/MARINE...Small