FXUS66 KLOX 160554 AAA AFDLOX Area Forecast Discussion...UPDATED National Weather Service Los Angeles/Oxnard CA 1054 PM PDT Thu Aug 15 2024 updated aviation discussion .SYNOPSIS...15/834 PM. A high pressure system in place over the region will weaken and move east over the coming days as an upper-level trough moves into the Pacific Northwest. A cooling trend with increased onshore flow will establish through the weekend, then some warming will develop over the early half of next week. && .SHORT TERM (THU-SUN)...15/911 PM. An upper-level ridge of high pressure remains over the southern California region this evening. A warm air mass in place with minimal marine layer induced low cloud coverage the last several days will start to transition as onshore flow strengthens Friday and over the weekend. An increasing onshore flow pattern will be brought to us by strengthening southwest flow aloft between high pressure system retreating to the east into Texas Panhandle and an upper-level trough digging into the Pacific Northwest. Night through morning low clouds and fog will become more pronounced along the beaches through the weekend, especially along the Central Coast where ocean water temperatures are cooler. With the shallow marine layer depth in place, any low clouds could form dense fog. A northerly surface gradient remains in place across the area this evening. Gusty Sundowner winds are surfacing right now and a wind advisory remains in effect across southwestern Santa Barbara County this evening. There is a chance that the advisory could be cancelled early as the KSBA-KSMX surface gradient is showing some signs of weakening this evening. With winds riding near advisory levels, the wind advisory was left intact for now and observations will be monitored closely. A few tweaks were made to temperatures to reflect the overall trend, otherwise the forecast is in reasonable shape. *** From Previous Discussion *** Broad high pressure aloft currently centered over the region will be bumped to the east towards Texas tomorrow, as a trough stalls west of Oregon. This will commence a stagnant upper level pattern, with SoCal located between a trough and the high pressure center. Temperatures will be within a few degrees of normal for most areas, however contrary some more typical patterns, coastal locations are more likely to be warmer than normal through the weekend. Tomorrow temperatures will warm slightly, followed by a cooling trend for the weekend, when 500 mb heights are lower and onshore gradients strengthen. Marine layer cloud coverage this morning was confined to west- facing Santa Barbara County, and this is expected to continue for tomorrow. Marine layer clouds are expected to increase somewhat this weekend as lower heights cause some lifting and onshore flow intensifies. A Wind Advisory is in effect from 4 PM this afternoon through 3 AM tomorrow morning for the Santa Barbara Southwest Coast and adjacent Santa Ynez mountains. While the general trend across high resolution models shows a slight decrease in Sundowner winds tonight, there remains a 50-70% chance of northwest winds tonight gusting at 35 to 50 mph. Sundowner wind are likely to occur again Saturday night. The dry and warm offshore winds will lead to daytime highs several degrees above normal across the whole Santa Barbara South Coast (including Santa Barbara City), today and Saturday. Monsoonal thunderstorm activity is not favored through the weekend, although the outer edge of a moisture surge may bring some high clouds to the region tomorrow afternoon. This moisture is expected to be too elevated to increase thunderstorm chances, which continues to be well under 10 percent. .LONG TERM (MON-THU)...15/244 PM. The latest ensemble members have come to good agreement on the general upper level heights for the region. Heights are expected to climb each day through Wednesday and will peak around 593 to 595 dam. Temperates will trend upwards along with the increase in heights with moderate HeatRisk impacts for a large portion of the region Tuesday and Wednesday. There is about a 15 percent chance that Heat Advisories will be needed for some deserts and valleys. Marine layer clouds will be shallow with minimal inland extend due to high 500 mb heights, however the overall onshore flow pattern in the long term will support overnight-to-morning clouds at times for the coasts. Monsoonal moisture transport into the region becomes a bit more likely on Tuesday and Wednesday, with about 20 percent of ensemble members hinting towards a favorable upper level flow pattern. Even so, at this point the chance of actual convection remains less than 10 percent. && .AVIATION...16/0553Z. At 05Z at KLAX, the marine inversion was 600 ft deep. The top of the inversion was 1500 ft with a temperature of 28 deg C. High confidence in generally CAVU 06Z TAFs for KPRB, KSBA, KOXR, KCMA, KBUR, KVNY, KPMD, KWJF. Exception is brief MVFR vsbys late tonight into Fri morning at KSBA, KOXR and KCMA. Moderate confidence in the 06Z TAFs for the LA coastal airfields. There is a 40%-50% chance of IFR cigs between 11Z to 17Z at KLAX and KLGB, and a 20% chance of these conds at KSMO. Moderate confidence in the 06Z TAFs for KSMX and KSBP. There is a 40-50% chance of VLIFR conds at KSMX between 11Z-16Z due to cigs/vsbys, and the arrival of cigs could be off by +/- 2 hours from TAF time. There is a 10%-20% chance of IFR-LIFR cigs/vsbys at KSBP between 12-15Z. KLAX...Moderate confidence in the 06Z TAF. There is a 40%-50% chance of IFR cigs between 11Z to 17Z, or that they occur only briefly during this time. There is also a 40%-50% chance of IFR cigs moving in aft about 09Z Fri night. No significant east wind component is expected. KBUR...High confidence in the CAVU 06Z TAF. && .MARINE...15/806 PM. For the outer waters from the Central Coast to San Nicolas Island (the outer waters), high confidence in Gale force wind gusts through late tonight. High confidence in Gales subsiding late tonight, with SCA level winds thru at least the weekend, with the exception of a 20% chance of Gale force wind gusts in the furthest northern outer zone Friday evening. For the nearshore waters off the Central Coast, moderate to high confidence in SCA level winds and/or steep seas through late tonight. There is a 40-60 percent chance of SCA conditions again Friday and Saturday during the afternoon to evening hours, then lower chances through early next week. On Tuesday, there is a 30 percent chance of SCA winds in the late afternoon and evening. For the Santa Barbara Channel, moderate confidence in winds below SCA levels tonight, except for possible local SCA gusts over the far western portion. Moderate confidence in conditions remaining below SCA level tomorrow, but higher chances Saturday through Tuesday, with a 30 percent chance of SCA winds over the western channel each late afternoon to evening period. In the Eastern portion, high confidence in conditions remaining below SCA level through the period. For the waters off L.A. and Orange Counties, high confidence in conditions staying under SCA levels through early next week. With a shallow marine layer, high confidence in dense fog with visibilities under 1 mile effecting the Central Coast waters through at least tomorrow morning. && .LOX WATCHES/WARNINGS/ADVISORIES... CA...Wind Advisory remains in effect until 3 AM PDT Friday for zones 349-351. (See LAXNPWLOX). PZ...Small Craft Advisory in effect until 3 AM PDT Friday for zone 645. (See LAXMWWLOX). Gale Warning in effect until 3 AM PDT Friday for zones 670-673-676. (See LAXMWWLOX). && $$ PUBLIC...Hall/Schoenfeld AVIATION...Sirard MARINE...Smith SYNOPSIS...Hall weather.gov/losangeles Experimental Graphical Hazardous Weather Outlook at: https://www.weather.gov/erh/ghwo?wfo=lox