801 FXUS66 KLOX 141230 AFDLOX Area Forecast Discussion National Weather Service Los Angeles/Oxnard CA 530 AM PDT Mon Sep 14 2020 .SYNOPSIS...14/342 AM. Night through morning low clouds and fog will remain confined to coastal areas for much of this week. Otherwise, high pressure aloft will keep mostly clear skies across the region, through there will be areas of smoke. Temperatures are expected to be above normal for most of the week, but will be dependent upon how thick the smoke layer is each day. Some cooling is expected at the end of the week into next weekend. && .SHORT TERM (TDY-WED)...14/409 AM. Low clouds were confined to the Central Coast and the Santa Ynez and Salinas Valleys this morning. The marine layer was still shallow so there was enough dense fog to warrant Dense Fog Advisories in these areas. Some patchy low clouds were trying to develop just west of L.A. County, but they will probably remain off the coast. Any low clouds should burn off by mid morning in most areas. An elongated upper high centered over Utah extended westward into southern and central CA this morning. This pattern will change very little through Wed, though the upper high will drift a bit westward Tue and Wed. The marine layer will remain shallow, and boundary layer relative humidity fields suggests that night through morning low clouds and fog will remain confined to coastal areas, and probably just the Central Coast. A weak eddy circulation tonight could send some low clouds into southern coastal sections of L.A. County, but odds are a bit against it. Heights and thicknesses will be rather high across the region through Wed, as will temps at 950 mb, actually edging upwards a bit by Wed. Onshore gradients will be rather weak. Overall, these conditions which would support temperatures well above normal each day, with the warmest day likely to be Wed. However, the thickness of the smoke in the atmosphere will play a large role in max temps each day. Early this morning, there were more stars visible in the sky, suggesting that the smoke layer may have thinned some. Of course, areas of thicker smoke may drift over the region from time to time. For this forecast, have gone with bit of warming each day, with temps above normal across most of the region. but not quite as high as they would be under smoke-free conditions. Where and if smoke remains thick, max temps will be lower than forecast. N-S gradients should be strong enough to produce some locally gusty sundowner winds across western portions of the Santa Ynez Range and the adjacent south coast of SBA County each evening, strongest Wed evening. .LONG TERM (THU-SUN)...14/449 AM. The EC and GFS show the upper ridge holding across the area into Thu, although heights come down a bit, so there might be some slight cooling. An upper low will move into the Pac NW Thu night and Fri with a trough extending southward into the forecast area. The EC is stronger with the trough and shows heights falling more than does the GFS. Both models show cooling on Fri, but the EC shows significantly more cooling. This system should, with any luck, help push any residual smoke to the east of the region The marine layer will deepen, and night through morning low clouds will become more widespread on the coastal plain, possibly pushing into the valleys by Fri night. However N-S gradients will likely be strong enough to produce some sundowner winds Thu night and Fri night. Winds should be stronger Fri night, when there will be some upper level support and subsidence behind trough axis. These northerly winds should also keep skies clear across southern SBA County and possibly coastal Ventura County Thu night and Fri night. Over the weekend, a broad upper trough will be located across CA, but heights will still be.between 582 and 587 dm. Expect night through morning low clouds and fog in most coastal and some valley areas Sat night/Sun morning. Max temps Sat and Sun look to be near to possibly slightly above normal, although there may be a fair amount of high clouds which would cut back on temps. && .AVIATION...14/1230Z. At 1142Z, the marine layer was around 500 feet deep around KLAX. The top of the inversion was around 1900 feet with a temperature near 26 degrees Celsius. S of Point Conception...High confidence with valley and desert TAFs through the period. Moderate confidence with coastal TAF sites. There is a 30% chance for VFR conds through 17z for KSBA, and 20% chance at KOXR,KLAX,KLGB. Confidence is good for similar conds tonight into Tue morning. N of Point Conception...Moderate confidence with VLIFR/LIFR CIGs for all taf sites. Scour out times +/- 90 minutes from 12z TAFs. There is good confidence for similar conditions for this evening through Tue morning. MVFR to VFR conditions are likely to continue in haze/smoke for coastal and valley terminals through at least this afternoon, then conditions could improve. KLAX...There is a 30% chance of VLIFR/LIFR CIGs between 13/18z. Otherwise, MVFR/VFR conditions in haze/smoke will likely persist through at least 20Z. There is a 30 percent of no LIFR to IFR conditions through 16Z. No wind impacts expected at this time. KBUR...Overall, skies will be clear, but some periods MVFR vsby conds due to smoke and haze are expected today. No wind impacts are expected through the period. && .MARINE...14/157 AM. Across the Outer Waters... Winds in the central outer waters are Small Craft Advisory (SCA) level with the strongest gusts around Point Conception. Winds across the entire outer waters will be SCA level by mid afternoon and will continue through early Tuesday morning. There is a sixty percent chance of SCA winds Tuesday through Friday across the region, primarily in the afternoon and evening hours. Otherwise, conditions will remain below SCA levels. Across the Inner Waters north of Point Sal... There is a 20% chance of SCA winds this afternoon through evening. Otherwise, conditions will remain below SCA levels through Friday. Across the Inner Waters south of Point Conception... There is a 30% chance of winds to SCA level across the far western portion of the SBA Channel this afternoon and evening, as well as the same period through Thursday. There is higher confidence for a SCA Friday evening, strongest across the western portion. Widespread dense fog will continue over the coastal waters, especially for areas north of Point Conception and through the Santa Barbara Channel through at least Thu. Patchy fog is possible off the coastal waters adjacent to Los Angeles and Ventura Counties. && .LOX WATCHES/WARNINGS/ADVISORIES... CA...Dense Fog Advisory in effect until 9 AM PDT this morning for zones 34>37. (See LAXNPWLOX). PZ...Small Craft Advisory in effect until 3 AM PDT Tuesday for zones 670-673. (See LAXMWWLOX). && .HAZARD POTENTIAL OUTLOOK (WED-SUN). No significant hazards expected. && $$ PUBLIC...DB AVIATION...Kaplan MARINE...Kaplan SYNOPSIS...DB weather.gov/losangeles