FXUS66 KLOX 281640 AFDLOX Area Forecast Discussion National Weather Service Los Angeles/Oxnard CA 940 AM PDT Wed Jul 28 2021 .SYNOPSIS...28/253 AM. Drier and warmer conditions can be expected across the area through Thursday as high pressure aloft strengthens. Low clouds and fog will continue to impact coastal areas during the night and morning hours. On Friday and Saturday, some monsoonal moisture may move into the area. For Sunday through early next week, warm and dry conditions are expected. && .SHORT TERM (TDY-FRI)...28/847 AM. ***UPDATE*** Marine layer stratus is still very much entrenched along the Central Coast this morning and quite patchy south of Point Conception. Clouds should clear from most areas by late morning, except some beaches along the Central Coast may not see any sunshine. High clouds are streaming in from a weak upper low off the coast as well as from the southeast, so some areas could be partly cloudy through the day. It should be a fairly quiet day, except for a slight chance of thunderstorms this afternoon over the eastern San Gabriel mountains and Antelope Valley, as well as the northern Ventura County mountains. Although not super impressive by any stretch, there is still a decent moisture influx with PWATs over 1" combined with some instability with CAPE of a few hundred J/kg. Especially with afternoon heating there could be some convective initiation late this afternoon. Any storm that develops will likely be short-lived with the best chance near the Kern and San Bernardino County borders. Otherwise it should be quite warm over the interior with some moderate onshore flow. Forecast looks to be in good shape and not planning any significant updates. ***From Previous Discussion*** A large upper high centered over the middle of the CONUS will continue to dominate the weather pattern over the next few days while keeping a weak trough over the coastal waters. As high pressure expands and strengthens slightly, the marine layer will be more shallow and remain limited to coastal areas over the next few days, with an outside chance that stratus filters into to a few coastal valleys. High temperatures will generally be a few degrees warmer over the next couple of days. Onshore gradients will remain fairly persistent over the next few days as well, therefore expect night through morning low clouds to continue, mainly for the coastal plain through the short term period. Some coastal valleys could see some stratus and patchy fog during late night into early morning hours. By Thursday night, the upper ridge will remain dominant across the west, but the center of the high will become more elongated SE to NW which will be conducive to draw in more monsoonal moisture across the mountains and desert. Latest models were hinting at a deeper mid level moisture plume moving into SE California from earlier thunderstorm activity across AZ, NV and NRN Mexico. If this comes to fruition, the outflow from these storms could bring another chance of afternoon and evening showers and/or thunderstorms across San Bernardino and Riverside Counties, as well as the eastern San Gabriel Mtns and Antelope Valley. The easterly wave aspect does not look quite as good, so seeing widespread showers across coast and valleys does not look good for our forecast area at this point, but that could chance. For now will keep slight chance POPs for the San Gabriel Mtns and Antelope Valley Fri afternoon and evening. High temps should be a few degrees cooler Fri due to the increasing cloud cover, but expect higher humidity levels making it feel pretty sticky once again. .LONG TERM (SAT-TUE)...28/408 AM. Both the GFS and ECMWF models remain in good agreement through the extended period with large scale feature. Synoptically the large expanded upper ridge that has been parked over the western half of the CONUS will become more amplified well into western Canada which in turn will keep an area of low pressure and associated trough sitting off the PAC NW and coastal waters down to the coastal waters off Southern California. In coordinating with surrounding offices, have kept in slight chance for showers and thunderstorms for the L.A. County Mountains and Antelope Valley Friday night into Saturday. One concern is that the upper trough will start to push slightly east towards SoCal as the upper high starts to shift eastward. This would cause the upper wind pattern to shift to the SW. The timing of the wind shift aloft could bring a drier pattern to L.A. County Mtns and Antelope Valley on Saturday which would mean the forecast for showers and thunderstorms would need to be pulled out. High temps will be a few degrees cooler on Saturday as onshore flow strengthens. There will continue to be more of a SW flow aloft which should keep any monsoonal moisture to the southeast Sunday through Tuesday with mostly sunny skies. Onshore flow will strengthen each day Sunday-Tuesday which should allow night through morning low clouds to become more widespread across the coastal plain and into coastal valleys. High temps will be near normal across coastal areas but around 3-5 degrees above normal across inland areas. && .AVIATION...28/1640Z. At 1630Z, the marine inversion at KLAX was based at 600 feet. The top of the inversion was 1900 feet with a temperature of 25 degrees Celsius. Overall, moderate to high confidence in 18Z TAF package. High confidence in CAVU conditions for valley/desert TAF sites. For coastal TAF sites, moderate confidence in coverage of CIG/VSBY restrictions as well as timing. KLAX...Overall, moderate confidence in 18Z TAF. High confidence in VFR conditions through this evening. For tonight, high confidence in return of IFR conditions, but low confidence in timing (could be +/- 3 hours of current 05Z forecast). No significant easterly winds are expected. KBUR...High confidence in 18Z TAF as CAVU conditions are expected. && .MARINE...28/739 AM. For the Outer Waters, moderate to high confidence in current forecast. For PZZ670, high confidence in forecast as winds and seas are expected to remain below Small Craft Advisory (SCA) levels through Sunday. For PZZ673/676, moderate confidence in current forecast. There is a 30-40% chance of SCA level winds during the afternoon and evening today and Thursday and again on Saturday and Sunday. For the Inner Waters north of Point Sal, high confidence in current forecast. Through Sunday, winds and seas are expected to remain below SCA levels. For the Inner Waters south of Point Conception, moderate to high confidence in current forecast. For the western half of the Santa Barbara Channel, there is a 20-30% chance of SCA level winds during the late afternoon and evening hours today through Saturday. Otherwise, high confidence in winds and seas remaining below SCA for the southern Inner Waters through Sunday. && .LOX WATCHES/WARNINGS/ADVISORIES... CA...NONE. PZ...NONE. && .HAZARD POTENTIAL OUTLOOK (FRI-TUE). Monsoonal thunderstorms are possible starting Friday and lasting through the weekend. && $$ PUBLIC...Stewart/Kaplan AVIATION...RAT MARINE...RAT SYNOPSIS...Kaplan/Hall weather.gov/losangeles