FXUS66 KLOX 281127 AFDLOX Area Forecast Discussion National Weather Service Los Angeles/Oxnard CA 427 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)...28/417 AM. Low clouds and fog are well-entrenched early this morning across the coastal and lower valley areas as stronger onshore flow continues to establish. 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. Some cooling should develop today as the trough approaches. Earlier AMDAR soundings from KLAX indicated the marine layer depth around 1300 feet deep, but it is likely lower than that along the Central Coast due to the trough positioning. Clouds are generally a little more extensive across the Southland versus this time last night, and less extensive along the Central Coast. The thinner marine layer depth along the Central Coast will permit dense fog to develop. A dense fog advisory was expanded from the Central Coast beaches to encompass all of the broader Central Coast sections and the Santa Ynez Valley. This advisory is in effect until 9 am PDT this morning. If you encounter dense fog on your morning travels this morning, slow down, use low beam headlights, and increase the space cushion around your vehicle. 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...28/0229Z. At 1758Z at KLAX, the marine layer was 1200 ft deep. The top of the inversion was 2100 ft with a temperature of 26 degrees Celsius. High confidence in the TAFs for KWJF, KPMD, and KPRB. Low to moderate confidence in remainder of TAFs. Timing of flight cat changes could be off by +/- 3 hours. Low confidence in arrival time of cigs. For KSBA, KOXR, KCMA, KSMO, and KLAX there is a 20% chance of VLIFR conds 07Z-15Z. For KBUR there is a 30% chance of VLIFR conds. KLAX...Low to moderate confidence in TAF. There is a 20% chance of 1/4SM FG and OVC002 conds between 08Z-15Z. Good confidence any significant east wind component will remain under 6 kt. KBUR...Moderate confidence in TAF. There is a 30% chance of 1/4SM FG and BKN002 conds 11Z-15Z. && .MARINE...27/819 PM. In the outer waters, there is good confidence in the forecast through Saturday morning, with winds expected to remain below Small Craft Advisory (SCA) levels. Then moderate confidence in winds increasing Saturday afternoon through Monday. SCA level wind gusts could occur (20% chance) during this time, especially Sunday and Sunday night, in the northern waters and near Point Conception. Winds are likely to weaken again Monday night through Wednesday, remaining well below advisory levels. For the inner waters north of Pt Sal, the Santa Barbara Channel, and inner waters from Pt Mugu southward, moderate to high confidence that winds and seas will remain below SCA levels through Tuesday night. There is a 10-20% chance of SCA level winds during the afternoon/evening hours on Saturday and Sunday, mainly in western and southern portions of the Santa Barbara Channel, and over the western portion of the waters from Anacapa Island to Catalina Island. Areas of dense fog with vsbys 1 NM or less are likely (50-60% chance) to affect the waters tonight through Saturday morning, most widespread off the Central Coast. && .LOX WATCHES/WARNINGS/ADVISORIES... CA...Dense Fog Advisory remains in effect until 9 AM PDT this morning for zones 340-346. (See LAXNPWLOX). Dense Fog Advisory in effect until 9 AM PDT this morning for zones 341-347-348. (See LAXNPWLOX). PZ...NONE. && $$ PUBLIC...Hall AVIATION...Phillips MARINE...Smith SYNOPSIS...Hall weather.gov/losangeles Experimental Graphical Hazardous Weather Outlook at: https://www.weather.gov/erh/ghwo?wfo=lox