FXUS66 KLOX 081728 AFDLOX Area Forecast Discussion National Weather Service Los Angeles/Oxnard CA 1028 AM PDT Thu Aug 8 2024 .SYNOPSIS...08/847 AM. Slightly cooler temperatures are expected today as increasing onshore flow brings cooler air to coast and valleys. A warming trend will return Friday and Saturday, with temperatures up to around 105 for far interior areas. Cooler temperatures are expected in all areas by next week as a trough of low pressure replaces the ridge along the West Coast. && .SHORT TERM (TDY-SAT)...08/902 AM. ***UPDATE*** Temperatures are again trending cooler to start the day as onshore flow is a little stronger. Marine layer stratus filled in across all the coastal areas this morning but is already pulling away from the LA coast. Expecting most coast/valley areas to be slightly cooler than yesterday, except some recovery expected after the huge 12 degree drop across the Salinas Valley yesterday. ***From Previous Discussion*** Upper level ridging will prevail across the forecast area today thru Sat, with H5 heights expected to be generally in the 592-593 dam range thru the period. Due to the orientation of the upper level ridging, monsoonal moisture will be limited over SW CA and remain well to the E of the area. There may be some afternoon cu buildups over the San Gabriel Mtns by Sat, otherwise minimal convection is expected. The marine inversion is forecast to be rather shallow the next few nights, at around 1000 ft or so tonight, and even shallower Fri night. Low clouds and fog are expected for much of the coast and some adjacent vlys tonight into Fri morning, then should be confined mainly to portions of the Central Coast and L.A. County coast Fri night into Sat morning thanks to some offshore pressure gradient trends both to the N and E. Patchy dense fog will also be possible again for the Central Coast tonight into Fri morning. The low clouds should clear to off the coast by late morning. Otherwise, mostly clear skies will continue over the forecast area thru Sat. Breezy onshore winds will continue each afternoon as well. Temps are expected to have a warming trend over the next couple of days, with triple-digit heat returning for Sat across the warmest vlys of L.A. County and lower mtns, and continue for the interior vlys and deserts. With warm overnight lows, heat stress will increase for much of the region away from the coast. Heat Advisories may become necessary by Sat for some of the mtns and interior vlys, and a possible Excessive Heat Watch or Warning cannot be ruled out for the Antelope Vly. .LONG TERM (SUN-WED)...08/333 AM. The GFS and EC deterministic and mean ensembles are in generally good agreement Sun and Mon with an upper level ridge persisting over srn CA. The GFS weakens the upper level ridging Tue and Wed as an upper level trof moves into the region. The EC, however, maintains the upper level ridge across srn CA thru Wed. The GFS is the cooler of the two models for Tue and Wed, so some uncertainty in the temp forecast for that period. Night and morning low clouds and fog are expected along the Central Coast and L.A. County coast Sat night thru Mon morning, then expand in coverage to many coastal areas and some adjacent vlys for Mon night thru Wed morning. Elsewhere and otherwise, mostly clear skies will prevail Sun thru Wed. Temps will be several degrees above normal away from the coast Sun, then cool to near normal to several degrees below normal across much of the region by Tue. However, as mentioned above, there is some uncertainty on the extent of cooling by Wed due to the model differences. If the EC forecast turns out to be more accurate, then temps will be potentially quite a bit warmer for many areas Tue and Wed than what is currently forecast. && .AVIATION...08/1728Z. At 1647Z at KLAX, the marine layer was 1200 ft deep. The top of the inversion was at 5100 ft with a temperature of 25 C. High confidence in TAFs for KPRB, KBUR, KVNY, KPMD, and KWJF. There is a 20% chance of brief IFR-MVFR conditions between 12Z and 15Z tonight at KBUR and KVNY Moderate confidence in LA Basin TAFs. 20% chance that cigs lower than 010 arrive at KLAX/KSMO between 03 and 06Z. 20% chance of vsbys less than 3SM between 06 and 15Z. 30% chance KLGB becomes IFR from 09-14Z due to cigs below 010. Low confidence in remaining coastal TAFs. Arrival time of cigs may be off +/- 3 hours from current forecast, and minimum flight cat may be off one cat at any point after cigs arrive. 40% chance of dense fog at KSMX, KSBP, KSBA; a 20% chance at KOXR; and a 10% chance at KCMA. KLAX... Moderate confidence in 18Z TAF. VFR conditions expected until 03Z. 20% chance of cigs lower than 010 to arrive between 03 and 06Z, and a 30% chance any cigs don't arrive until 06Z. Between 06 and 15Z, there is a 20% chance of vsbys below 3SM. VFR conditions expected by 18Z tomorrow, but there is a 30% chance of VFR conditions by 15Z tomorrow. No significant east wind component expected throughout the forecast period. KBUR...High confidence in the 18Z TAF. There is a 20% chance of IFR-MVFR conds between 12 and 15Z. && .MARINE...08/842 AM. In the Outer Waters, moderate to high confidence in the forecast. Low end Small Craft Advisory (SCA) level winds are expected in the two northern zones (PZZ670/673) beginning this afternoon thru late tonight, thus a SCA was issued. There is a 30-40% chance that SCA level winds continue tonight thru tomorrow. For the southern outer zone (PZZ676), there is a 40-50% chance of low end SCA level winds occuring this afternoon thru late tonight. Friday through Monday night, there is a 70-80% chance of SCA level winds in all outer zones, with best chances in the afternoon thru evening hours. For the Inner Waters N of Pt. Sal, moderate to high confidence in the forecast. Thru Fri morning, high confidence in winds and seas remaining below SCA levels. For Friday afternoon/eve, there is a 30-40% chance of SCA level winds. From Saturday thru Monday night, there is a 50-60% chance of SCA conds in the afternoon/eve hours. In the Inner Waters S of Pt. Conception, high confidence in the forecast. Winds and seas should remain below SCA levels thru Monday night. The exception is in the western half of the Santa Barbara Channel where there is a 30-40% chance of SCA level winds during the late afternoon/eve hours Friday thru Monday. Tropical Storm Emilia well to our south could produce some long period southerly swell in our waters by tonight or Friday. && .LOX WATCHES/WARNINGS/ADVISORIES... CA...NONE. PZ...Small Craft Advisory in effect from 3 PM this afternoon to 3 AM PDT Friday for zones 670-673. (See LAXMWWLOX). && $$ PUBLIC...MW/Sirard AVIATION...Lewis MARINE...Lewis/DB SYNOPSIS...MW weather.gov/losangeles Experimental Graphical Hazardous Weather Outlook at: https://www.weather.gov/erh/ghwo?wfo=lox