870 FXUS66 KLOX 251701 AFDLOX Area Forecast Discussion National Weather Service Los Angeles/Oxnard CA 1001 AM PDT Wed Sep 25 2019 .SYNOPSIS...25/855 AM. Temperatures will cool several degrees on the Central Coast and most valleys today. There will be widespread cooling on Thursday and remain cool into early next week. There is a slight chance of light rain or drizzle Thursday through Saturday from Point Conception and southward. && .SHORT TERM (TDY-FRI)...25/1001 AM. Impressive coastal inversion on the KVBG sounding this morning, going from 56 degrees at the surface to almost 90 at 1000'. This is actually stronger and warmer than yesterday, however the big difference today is the much weaker northeast flow in the boundary layer. So while it will still be warm in the hills and inland areas we'll see much cooler temps at the coast which got a big boost yesterday from the downsloping winds. Similar trends farther south though to a lesser degree as we've lost the upper wind support but gradients are still weakly offshore. A shallow marine layer returned as expected and we're already starting to see the beginnings of a southerly surge around Pt Conception as the stratus is creeping around the corner there and should start to fill in the northern waters through the day and into the evening. ***From previous discussion*** A big onshore push (esp to the north) set up tonight and Thursday. It will produce a southerly surge and low clouds will rapidly advance up the coast...around Pt Conception and into the Central Coast. Clouds will cover the all of the coasts and vlys by dawn. the wrap around from the upper low will bring mid level clouds to all of LA county and the slight chc of rain will continue over the eastern portion. The clouds and the onshore flow will bring widespread cooling to the area with max temps dropping 10-15 degrees inland Thu and 5-10 near the coast. Vly temps will be below normal while inland and coastal temps will be pretty close to normals. Dry NW 585 DM flow sets up over Srn Ca on Friday. But the low level flow will really determine the days weather. Quickly increasing onshore flow will lift the marine layer to over 3000 feet. Low clouds will cover the coasts and vlys and will reach the coastal slopes. There will be slow to no clearing across the coast and probably partly cloudy skies over the vlys. The rapid lifting of the marine layer will create local drizzle across the coasts and vlys esp near the foothills. Anther day of significant cooling with most coast and vly locations falling 5 to 10 degrees. Max temps across all the coast and vlys will be in the upper 60s and 70s. Max temps will below normal everywhere but esp the vlys where they will be about 10 degrees blo normal. .LONG TERM (SAT-TUE)...25/314 AM. Just when you thought the cooling trend couldn't go on any longer along comes an early season trof. The trof assoc with a 545 DM upper low in Washington State will move through CA on Saturday. The marine layer will be so deep that clouds (hard to call them low when some bases may be near 5000 feet) will not only cover the coasts and vlys but will extend deep into the mtn passes and some interior vlys. There will be patchy drizzle in the morning and the trof will produce enough lift over LA county to bring a chc of rain. Aside from some downsloping warming across the SBA south coast there will be more cooling esp inland where max temps will fall about 10 degrees. Broad cyclonic flow will continue over the area Sunday. There will be another round of extensive morning clouds. Almost all of the lift will be gone so the chc of showers or drizzle will be insignificant. Max temps will not change much from Saturday and will remain on the cool side. Low confidence cloud forecast for Monday - there should be enough cool air and mixing to eliminate the marine layer and any low clouds. But there will still be onshore flow and cyclonic turning aloft so it would not be surprising to see low clouds. There will be a little warming as the airmass modifies but still on the cool side. Ridging begins to move in on Tuesday and sfc grads will trend offshore this should kick off a decent two day warming trend. && .AVIATION...25/1255Z. At 1224Z at KLAX, the marine layer was 1100 feet deep. The top of the inversion was near 2700 feet with a temperature of 26C. Moderate confidence in KSMO, KLAX, KLGB, and KOXR TAFs through 18Z, as VFR transition could occur +/- an hour from forecast. For KSBA and KCMA, there is a 40% chance of IFR/LIFR conditions 14Z- 18Z. For remaining TAFs, high confidence through the morning. Good confidence in all TAFs 18Z-02Z, then lower confidence as arrival of IFR/MVFR conditions could occur an hour earlier than forecast. KLAX...Moderate confidence in TAF. IFR cigs could arrive as early as 13Z. VFR transition could occur as early as 16Z. Arrival of low clouds tonight may occur as early as 02Z. There is a 30 percent chc of an 8 kt east wind component through 16Z this morning. There is a 20 percent chc of a 15 kt east wind component after 26/08Z. KBUR...High confidence in TAF through 06Z, then moderate confidence. There is a 60% chance of MVFR conditions that could occur as early as 06Z. There is a 30 percent chc of 15015KT winds after 26/02Z. && .MARINE...25/904 AM. Winds across the coastal waters are expected to shift southeasterly today and should largely remain under Small Craft Advisory (SCA) level through the afternoon. SCA level SE winds are likely over the outer waters along the Central Coast and south towards the Channel Islands as well as the Santa Barbara Channel tonight through Thursday afternoon. There is a 40% chance that SCA level winds may extend southward. Otherwise winds and seas are expected to remain below SCA level through the work week for all of the coastal waters. There is a 60% chance of SCA level NW winds across the waters from the Central Coast towards San Nicolas Island during the afternoon and evening hours of Saturday and Sunday, and a 40% chance for the western portion of the Santa Barbara Channel for the same time period. Long period south swell is likely to impact the waters on Friday through the weekend. && .LOX WATCHES/WARNINGS/ADVISORIES... CA...NONE. PZ...Small Craft Advisory in effect from 9 PM this evening to 3 PM PDT Thursday for zones 650-670-673. (See LAXMWWLOX). && .HAZARD POTENTIAL OUTLOOK (FRI-TUE). No significant hazards expected. && $$ PUBLIC...MW/Rorke AVIATION...Stewart MARINE...Sweet/Stewart SYNOPSIS...B weather.gov/losangeles