613 FXUS66 KLOX 132218 AFDLOX Area Forecast Discussion National Weather Service Los Angeles/Oxnard CA 218 PM PST Wed Nov 13 2019 .SYNOPSIS...13/1143 AM. Clouds will increase today with high temperatures just a few degrees above normal. Cloudy conditions and onshore winds will keep cooler temperatures around for the rest of the week, but skies should become clear for the weekend. Expect overnight to morning clouds and fog near the coast through Friday. && .SHORT TERM (TDY-SAT)...13/218 PM. A cooler day with onshore flow and an abundance of high clouds from a trough to our west. Looking for at least one more day and probably two of a mixture of clouds at various levels and cool onshore flow. Skies won't be mostly cloudy the entire time but as bands of thicker clouds come through they will be enough to block or reflect a good portion of the sun's rays. Some deepening of the marine layer is expected as the trough gets closer and temps cool aloft but the higher clouds often cause a significant disruption in the marine layer so confidence is low on that particular aspect of the forecast, which mostly impacts aviation much more so than the general public. Over the weekend gradients will trend strongly offshore as surface high pressure develops to our northeast following the passage of the trough into the Plains. This will set up another weak to moderate Santa Ana wind event, but mainly for Sunday. For Saturday some locally breezy winds but the main impact will be a big jump in temps into the 80s to lower 90s for most coast/valley locations. .LONG TERM (SUN-WED)...13/216 PM. The 12z ECMWF and a few of its ensemble members are trending a little stronger with the offshore event which is expected to peak on Sunday. And as has been the case virtually the entire Fall the GFS is weaker. Typically the stronger EC has verified best this season but in a couple cases it was overdone. Given the minimal upper support the feeling still is that this will be a sub- advisory level wind event but with very warm (perhaps record- breaking) temps and very low humidities. Gradients are weaker Monday but the the ridge will linger into Monday evening so for some areas (especially inland) Monday will be just as or even warmer than Sunday. But with less wind. The ridge shifts east Tuesday as a cold upper trough drops out of Canada. Tuesday should be quite a bit cooler with a strong onshore trend and a likely return of the marine layer. Then the forecast gets tricky around mid week and beyond as the deterministic models continue to hold onto their respective biases in terms of trough placement. Looking at the ensembles though there is more agreement on a continuation of the inside slider pattern which the deterministic GFS is currently favoring. Inside sliders are typically moisture-starved, however leading up to their arrival they often spin up a big eddy circulation with rapid cooling and moistening up to 850mb or so. This scenario is not uncommon this time of year and typically results in some drizzle/light rain, especially LA County, that can continue into the afternoon hours. So low pops have been introduced for Wednesday in LA County. The EC ensemble solution would likely be a little wetter and possibly linger into Friday, but still mostly a drizzle/light rain event at most. There are outlier solutions with considerably more precip but very low odds on that happening. For now will lean towards the GFS ensembles with high confidence in significant cooling but low confidence on precip chances and amounts. && .AVIATION...13/1851Z. At 1716Z at KLAX, the marine layer was around 900 feet deep. The top of the inversion was at 2000 feet with a temperature of 20 C. Low confidence in coastal TAFs, especially with regards to timing of flight category transitions. All sites that do not have 1/4SM FG have a 20% chance of it after about 10z. VFR conditions will last the afternoon, before a return of the marine clouds early this evening. Moderate confidence in valley TAFs, although there is a non-zero chance of marine clouds making it into the valley sites overnight. KLAX...Low confidence in 18z TAF. Frequent changes in the visibility and ceiling are likely tonight into Thu morning with little confidence in when or if such changes will occur. KBUR...Moderate confidence in TAF. There is a 30% chance that cigs will sneak into the airfield early Thursday. && .MARINE...13/206 PM. For all of the coastal waters, high confidence that winds and seas will remain below Small Craft Advisory (SCA) level through Thursday. Moderate confidence that winds will increase to SCA level over the offshore waters along the Central Coast and southward towards San Nicolas Island on Friday afternoon and last through the night. Lower confidence on whether the SCA level winds will continue into Saturday, as winds are likely to weaken. Patchy dense fog with visibility of one nautical mile or less is expected to impact all of the coastal waters through tonight. A large and long period NW swell is expected to arrive over the coastal waters on Friday afternoon and last through the weekend, with the largest impacts along the Central Coast. && .LOX WATCHES/WARNINGS/ADVISORIES... CA...NONE. PZ...NONE. && .HAZARD POTENTIAL OUTLOOK (SAT-WED). There is the potential for moderate Santa Ana winds Sunday with elevated to critical fire weather conditions possible. && $$ PUBLIC...MW AVIATION...Sweet/Stewart MARINE...Sweet SYNOPSIS...Phillips weather.gov/losangeles