310 FXUS66 KLOX 140344 AFDLOX Area Forecast Discussion National Weather Service Los Angeles/Oxnard CA 844 PM PDT Sun Apr 13 2025 .SYNOPSIS...13/843 PM. A gradual cooling trend is expected into early this week, then more significant cooling will take place by late week. Night through morning low clouds and fog can be expected, pushing into the coastal slopes of the mountains by mid week. A cold upper level low pressure systems is forecast to bring showers to the area on Friday, and even a thunderstorm cannot be ruled out especially in the mountains and deserts. Dry and milder conditions can then be expected next weekend. && .SHORT TERM (SUN-WED)...13/842 PM. Weak closed upper level low pressure system spinning off the coast of Southwest California tonight. This in combination with moderate onshore flow resulting in low clouds and patchy fog making a quick return to many coastal areas this evening. With the marine layer depth still around 1500 feet, expecting low clouds and patchy fog to fill in across most coastal/valley areas overnight into Monday morning, and could even see some patchy drizzle. Another weak upper low well west of Baja this evening is expected to track east-northeast and open up as an upper level trough as it comes ashore over northern Baja by late Monday afternoon. This system will tap into some mid level moisture and with the upper flow turning southeasterly, looking for mid level clouds to be on the increase across Southwest California by Monday afternoon/evening. 00Z NAM model showing an embedded vort max in the upper level flow that could bring some additional energy/organization to the mid level moisture field. Models also showing some increased instability Monday afternoon into Monday evening. While sounding profiles showing much of the moisture rather elevated and limited, there is around a 5 percent chance of an elevated thunderstorm on Monday afternoon/evening. *** From previous discussion *** The marine inversion is expected to be around 1500-1700 ft or so for the most part tonight thru Tue, then deepen to 2500-3000 ft Tue night into Wed morning. Overall, it looks like a marine layer pattern will prevail across the forecast area during the period. Night and morning low clouds and fog can be expected along the coast and into many of the vlys, and even extending to the lower coastal slopes Tue night into Wed morning. The low clouds will clear back toward the coast each afternoon thru Tue with many beaches having only partial afternoon clearing. The low clouds may persist for many areas on Wed, even into some of the vlys. There also should be enough of an onshore push for patchy drizzle over the coast and vlys S of point Conception later Mon night into Tue morning. Otherwise, clear to partly cloudy skies with mainly some mid and hi clouds at times can be expected. Winds through Wed should be generally weak during the night and morning hours, with breezy to gusty S to W winds in the afternoon and early evening. However, stronger gusty SW winds should affect portions of the L.A. County mtns and deserts on Wed thanks to a fcst of a +10.3 mb LAX-DAG Wed pressure gradient in the afternoon. Temps should cool down slightly for Mon, with inland areas remaining several degrees above normal while coastal and some adjacent vlys continue to be around or a few degrees below normal. For Tue, further cooling from the coast to the coastal slopes should prevail, while the interior vlys, mtns and deserts remain a few deg above normal. By Wed, more significant cooling is expected, with just about all areas falling to about 4 to 10 deg below seasonal norms. Highs on Mon for the warmest vlys and lower mtns should be in the mid to upper 70s, except lower to mid 80s in the Antelope Vly, then fall to the lower 70s on Tue, except to around 80 in the Antelope Vly, and to the mid to upper 60s on Wed, except lower 70s in the Antelope Vly. .LONG TERM (THU-SUN)...13/206 PM. The models are in mostly good agreement in the extended period. On Thu, a significant and cold upper level low will move into the northern and central Great Basin, then quickly dive S and into southern and southeastern CA on Fri. The upper level low will move E of the region on Sat with a broad NW to N flow aloft. H5 heights will rebound on Sun to near 573 dam with a broad NW flow aloft. The marine layer pattern will persist into Thu with night and morning low clouds for the coast and vlys, possible even up to the coastal slopes. Otherwise partly cloudy skies overall can be expected. For Fri, the proximity of the upper level low will bring the slight chance to chance of showers to much of the region, mostly in the afternoon hours. The cold air aloft (GFS fcst as low as -25 deg C at H5) will also contribute to increased instability with the slight chance of thunderstorms introduced into the fcst for Fri afternoon, especially over the mtns and deserts. There is still some uncertainty on the exact track of the upper level low and where the coldest air aloft moves to, but we should have better confidence in this with additional model runs as we draw closer to the middle of next week. Any leftover showers will end Fri evening, with dry and milder conditions expected on Sat then turning warmer on Sun with some coastal low clouds and fog in the night and morning. Temps are expected to cool to significantly below normal for mid- April on Thu and Fri before turning a bit warmer on Sat and Sun, but remaining a few deg below normal for the most part. The warmest day overall during the extended period should be next Sun with the warmest vlys and lower mtns reaching the low to mid 70s. && .AVIATION...14/0017Z. At 0010Z at KLAX, the marine layer was around 1500 feet deep. The top of the inversion was around 2600 ft with a temp of 19 C. Moderate confidence in all TAFs, except high confidence in desert TAFs. Cigs likely to redevelop tonight across most coastal/valley YAF sites except KPRB. Timing of flight cat changes may be off by +/- 3 hours. Cigs may drop one flight cat lower than forecast overnight. KLAX...Moderate confidence in TAF. There is a 20% chc of LIFR cigs tonight. Good confidence that any E wind component will remain under 6 kt. KBUR...Moderate confidence in TAF. There is a 30% chc that cigs will arrive as early as 06Z Mon. && .MARINE...13/753 PM. Winds have subsided below Small Craft Advisory (SCA) levels, however seas may linger around/just below 10 feet across the outer waters into this evening. Otherwise, SCA conds are not expected across all the coastal waters through Thursday night. && .LOX WATCHES/WARNINGS/ADVISORIES... CA...NONE. PZ...NONE. && $$ PUBLIC...Gomberg/Sirard AVIATION...Gomberg MARINE...Lund SYNOPSIS...Sirard weather.gov/losangeles Experimental Graphical Hazardous Weather Outlook at: https://www.weather.gov/erh/ghwo?wfo=lox