FXUS66 KLOX 281631 AFDLOX Area Forecast Discussion National Weather Service Los Angeles/Oxnard CA 931 AM PDT Sat Sep 28 2024 .SYNOPSIS...28/417 AM. Some cooling will occur today as a weak low pressure area off the coast meanders toward the region and strengthens onshore flow. A persistent marine layer will keep the coastal areas below normal through Sunday with areas of morning dense fog. Warmer than normal conditions will continue away from the coast through Sunday. A warming trend will develop for early next week as onshore flow will weaken beneath a building ridge high pressure. && .SHORT TERM (TDY-MON)...28/931 AM. ***UPDATE*** The marine inversion this morning was around 1400 to 1500 ft deep. Extensive low clouds and fog affected the coast and much of the adjacent vlys into mid morning. The low clouds will clear back to or off the coast before noon, with some beaches probably remaining mostly cloudy thru the afternoon. Otherwise,look for mostly sunny skies across the forecast area thru this afternoon. Breezy onshore flow will prevail this afternoon, with the highest gusts in the Antelope Vly. Temps today will range from a few degrees below normal along the coast to 10-15 deg above normal for the interior vlys, mtns and deserts. Highs should reach the 60s to near 70 at the beaches, 70s to near 80 for the inland coast, 80s to mid 90s for the vlys and lower mtns, and 90s to around 100 for the Antelope vly. ***From Previous Discussion*** Onshore flow and a persistent marine layer are likely to remain in place across the region through Sunday as an upper-level trough, sitting about 275 miles southwest of Point Conception, advances on the southern portion of the state. A blocking upper- level ridge of high pressure over the Sonoran Desert this morning will strengthen over the coming days and inhibit the trough's eastward movement. The trough will run into the ridge on Sunday over Los Angeles County and be turned back. 500 mb heights will climb and onshore flow will weaken as the trough retreats to the southwest of the region for early next week. Some semblance of an onshore flow could remain intact for early next week, albeit much weaker than it has been. The forecast continues to take a warmer than NBM stance for Monday and beyond to account for most of the warming taking place across the interior. .LONG TERM (TUE-FRI)...28/425 AM. A warming trend will continue into Tuesday and possibly Wednesday as high pressure aloft to the east will continue to win the battle, pushing the trough to the southwest and warming the air mass. An offshore low-level flow component will set up between Monday and Wednesday, potentially pushing temperatures higher than forecast. Temperatures break away from NBM mean values and emphasize values closer to the 75th-90th percentiles, and buying more heavily into EPS temperature means, which have consistently advertised a warmer pattern developing in weak offshore flow. There is a moderate chance that Tuesday and Wednesday could be warmer than forecast as fair amount of the higher resolution EPS perturbations advertised much warmer temperatures than forecast. Much will depend upon how much monsoonal moisture and additional clouds seep into the area. A southeast low-level flow pattern develops between Monday night and Wednesday. The forecast ensemble members suggest precipitable water value means approaching between 0.8 and 0.9 inch across the region, which is on the order of 125 to 150 percent of normal for this time of year across the southern portion of the area. EPS members suggest a few solutions with QPF at sites across the region, but this would rely on convective model processes working as advertised. PoPs remain above NBM values across the terrain of the region as there is a non-zero chance of afternoon and evening showers and thunderstorms between Tuesday and Wednesday. The forecast ensemble spreads increase substantially for late next week. While temperature means suggest some cooling across the region as the trough will move back once again, the trough's movement remains in question at this point. The forecast goes with NBM values for late next week and reintroduces a broader low cloud field into the forecast. && .AVIATION...28/1239Z. At 12Z at KLAX, the marine layer was 1400 ft deep. The top of the inversion was at 2800 ft with a temperature of 24C. High confidence in the TAFs for KWJF, KPMD, and KPRB. Otherwise, nearly a repeat of yesterday morning at this time. Low clouds were widespread in all coastal areas and the Santa Ynez and San Gabriel Valleys. Clouds have pushed into the portions of the valleys of VTU County and the southeastern San Fernando Valley as well. Conds were mostly LIFR to VLIFR, except IFR across coastal sections of L.A. County. Skies should clear by mid morning in the valleys, and by noon on most of the coastal plain. However, clouds will likely linger into the afternoon near the beaches, especially across southern SBA County and Ventura County. Expect clouds to overspread the coastal plain this evening, and push into most valley locations after midnight. Conds should be mostly IFR to LIFR, except locally VLIFR on the Central Coast and in the valleys. KLAX...Low to moderate confidence in the 12Z TAF. There is a 30% chance that cigs will linger until as late as 22Z. There is a 20% chance that cigs will not clear at all. There is a 20% chance that cigs will arrive as early as 01Z. Good confidence that any east wind component will remain under 6 kt. KBUR...Moderate confidence in the 12Z TAF. There is a 20% chance that cigs will clear by 15Z. There is a 20% chance that LIFR to VLIFR conds will arrive as early as 10Z. && .MARINE...28/843 AM. In the Outer Waters (Central Coast to San Nicolas Island), high confidence in the forecast thru Sun morning, with winds expected to remain below Small Craft Advisory (SCA) levels. There is a 20% chance of a brief period of SCA level winds around Pt. Conception this afternoon/eve. SCA level winds are likely (60-70% chance) for Sun afternoon thru evening. Steep seas are likely this afternoon thru late Sunday, however, they will likely not have a short enough period to meet SCA thresholds. Then, moderate confidence in sub advisory winds Monday thru late Wednesday. For the inner waters north of Pt Sal, the Santa Barbara Channel, and inner waters off the LA and OC Coast, moderate to high confidence that winds and seas will remain below SCA levels thru Wed night. However, there is a 30-50% chance of SCA level winds Sun afternoon thru evening across the inner waters north of Pt. Sal, and a 20-30% chance in the western and southern portions of the Santa Barbara Channel, from Anacapa Island to Point Dume, and thru the San Pedro Channel. Areas of dense fog with vsbys 1 NM or less will affect the waters thru at least tomorrow morning in the evening thru early morning hours, most widespread off the Central Coast. && .LOX WATCHES/WARNINGS/ADVISORIES... CA...NONE. PZ...NONE. && $$ PUBLIC...Hall/Sirard AVIATION...DB MARINE...Lewis/DB SYNOPSIS...Hall weather.gov/losangeles Experimental Graphical Hazardous Weather Outlook at: https://www.weather.gov/erh/ghwo?wfo=lox