FXUS66 KLOX 280435 AFDLOX Area Forecast Discussion...UPDATED National Weather Service Los Angeles/Oxnard CA 935 PM PDT Fri Sep 27 2024 .SYNOPSIS...27/718 PM. High pressure to the east will weaken some through Tuesday as a weak low off the coast meanders toward southern California. Coastal areas will remain mild under a persistent marine layer through Sunday with areas of morning dense fog. Interior areas will remain warmer than normal but with slight cooling each day. Southeast to northeast flow will bring some warming to most areas Monday through Wednesday, especially coastal and valley areas. && .SHORT TERM (FRI-MON)...27/912 PM. ***UPDATE*** The main forecast issue for the short term update will be the coverage of low clouds and fog for coastal areas, some of the coastal valleys, and the coastal waters. Areas of dense fog are not included for the Central Coast with visibilities there expected to lower to 1/4 mile or less this evening through Saturday morning. A dense fog advisory has been issued for the San Luis Obispo and Santa Barbara sections of the Central Coast. Further south from the Santa Barbara South Coast to LA County, believe that ceilings will be a bit higher, with fog less of a concern. Low clouds are expected to extend somewhat into the coastal valleys, including the San Gabriel and eastern San Fernando Valleys, and portions of the Ventura Valleys. Temperatures should lower a few degrees over the interior tomorrow, but will likely change little near the coast where cloud cover could linger over/near the beaches into the afternoon hours. ***From Previous Discussion*** High pressure remains parked over Arizona while a closed low remains 300 miles to the west. The low is expected to slowly move towards and over southern California by Sunday and Monday. Low clouds and fog continue to hug the coast this afternoon, and looks settled in to remain the dominant feature for the coastal weather through at least Sunday. With onshore pressure gradients changing little through Sunday, and high pressure weakening aloft, expect gloomy skies to continue each night and morning over all coastal areas and a few more coastal valley areas. Some beaches will be slow to clear in the afternoon. Dense fog will continue to be possible, especially on the Central Coast. Interior areas have been running 10 to 15 degrees above normal, but will lower a few degrees each day as the high pressure aloft weakens. .LONG TERM (TUE-FRI)...27/129 PM. The picture gets more complicated Sunday Night through Wednesday. As the low currently off our coast approaches the area, computer projections are struggling as usual with a cut off low as to exactly where it will go and when it will get there. The projections of the track of the center of the low are sprayed from Ventura County to Imperial County. All tracks will weaken onshore flow and bring noticeable warming (at least to coastal areas), but exactly how much is very sensitive to the track. If it tracks more towards Ventura County, the airmass will actually cool a little and any warming will only be driven by the weaker onshore flow and the complicated marine layer response to the southeast winds aloft. If it tracks more towards Imperial County however, the entire airmass will warm (higher 500 mb heights) and the winds will be out of the northeast with possible low-end Santa Ana winds. This would result in a major warm up over the coastal and valley areas. To put some numbers behind this, the coolest 5% of the NBM projections for Wednesday have inland high temperatures generally between 80 and 90, while the hottest 5% have highs between 100 and 110. The current official forecast is more towards the middle, but leaning a little into the hotter solutions if for no other reason than to play it safe. The other wrinkle is a slight influx of monsoonal moisture. Precipitable water values increase from 0.4 inches on Monday to 0.8 inches on Tuesday. Usually that is not enough to worry about, but if it ends up being on the hotter end of projections, any moisture has an outside shot of forming a shower or thunderstorm. By Thursday or Friday, the vast majority of projections slide the low back to the west, which would return conditions back to something like what we are seeing today. && .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 in effect until 9 AM PDT Saturday for zones 340-346. (See LAXNPWLOX). PZ...NONE. && $$ PUBLIC...Kittell AVIATION...Phillips MARINE...Smith SYNOPSIS...Kittell/Smith weather.gov/losangeles Experimental Graphical Hazardous Weather Outlook at: https://www.weather.gov/erh/ghwo?wfo=lox