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663 FXUS66 KLOX 231311 AFDLOX Area Forecast Discussion...UPDATED National Weather Service Los Angeles/Oxnard CA 611 AM PDT Wed Apr 23 2025 .SYNOPSIS...23/333 AM. A persistent marine layer with stronger onshore flow will keep a cooler weather pattern in place through Saturday. Night through morning low clouds and fog with drizzle will be a staple of the forecast with clouds struggling to clear from beaches each day. Gusty onshore winds are possible across the interior portions of the area through the end of the week. A warming trend is expected for next week. && .SHORT TERM (TDY-FRI)...23/440 AM. The latest fog product imagery shows low clouds and fog extending into the coastal slopes of the mountains across the Southland and into the interior valleys of San Luis Obispo County. Earlier AMDAR soundings from KLAX around 07Z indicated a marine layer depth near 2100 feet deep, but that was several hours ago, and the marine layer has deepened substantially since. From looks of the satellite imagery combined with NAM BUFR time height sections, the marine layer depth is close to 3500 feet deep currently. If NAM BUFR time height sections play out as advertised, the marine layer depth should top out around 4000 feet deep later this morning. With the marine layer depth deepening substantially, drizzle is possible as weak dynamics with a shortwave trough move over the region and interact with the deep marine layer cloud deck this morning. Some rain gauges in southern Santa Barbara County are starting to pick up a few tips due to heavy drizzle. A deep marine layer depth is likely to continue to remain in place over the coming days as broad troughing remains anchored along the California coast and strong onshore flow will remain intact. A cooler pattern will linger into late week with temperatures below seasonal normals. Weak dynamics aloft will continue to scrape the area and bring the possibility of night through morning drizzle. Across the interior portions of the area, stronger onshore flow will bring much breezier to windier conditions during the afternoons and evenings. A wind advisory was added for the western Antelope Valley foothills for this afternoon and this evening where gusts up to 45 mph are possible. Isolated gusts to 55 mph cannot be ruled out near Lake Palmdale. With similar onshore pressure gradients developing over the coming days, additional wind advisory headlines may be needed. By Friday, an elongating trough in the Gulf of Alaska will enter the region while splitting off from the flow aloft. This cutoff trough will likely deepen the marine layer depth between Friday and Saturday to turn it into a deep moist layer up to around 7000 to 8000 feet deep on Friday night. This will be plenty deep enough to produce night through morning drizzle or light rain across the region. Mountain showers seems to be a high probability given the pattern and favorable flow pattern. .LONG TERM (SAT-TUE)...23/441 AM. The cutoff trough will approach the California coastline on Saturday morning as the marine layer mixes out into a deep moist layer. The forecast ensemble members introduce a majority of the perturbations with light rain across the area. EPS members are the wettest relative to the GEFS and CMC ensemble members. Almost all of the EPS ensemble members have precipitation across the region with amounts lessening as one heads south. EPS QPF means suggest a quarter inch or less, with a high chance of values between 0.25 and 0.50 inch for San Luis Obispo County. Meanwhile, GEFS and CMC keep the forecast more inline with night through morning drizzle. Given the cutoff trough, the current forecast generally keeps NBM values for PoPs, while skewing PoPs higher along the coastal slopes of the mountains. Temperatures will be much cooler than normal on Saturday with most areas being 5-12 degrees below normal. Temperatures in the mid 50s to mid 60s will be common across the coastal and valley areas. Experimental data analysis on the NBM forecast suggests KLAX and KOXR potentially seeing record low maximum temperatures on Saturday. Local records versus the forecast indicate otherwise, but near record low maximum temperatures will be possible on Saturday. A warming trend for much of next week is expected as cluster analysis still favors an upper-level ridge of high pressure building into the West Coast. Anomalously high heights seem more plausible across the Pacific Northwest, but the pattern will still likely create above normal temperatures with less marine layer low cloud coverage. && .AVIATION...23/1305Z. At 12Z at KLAX, the marine layer was 3400 feet deep. The top of the inversion was at 4700 feet with a temperature of 14 C. Clouds were widespread across the region, and have pushed into all areas except for the Antelope Valley, the mountains above 4000 feet, and the far interior valleys of SLO County. Conds were mostly MVFR to high IFR, except LIFR to VLIFR in the higher valleys, foothills and lower mountain slopes, with local LIFR cigs on the Central Coast and in the Santa Ynez Valley. Expect skies to clear by late morning in the valleys and early afternoon across interior portions of the coastal plain. Cigs will likely linger all day the coast, especially south of Pt. Conception. Expect widespread low clouds tonight, with MVFR cigs in most areas, except for IFR to VLIFR conds once again in the higher valleys, foothills and lower mountain slopes. KLAX...Moderate confidence in TAF. There is a 30% chance that cigs will scatter out between 20Z and 02Z. There is a 30% chance of an east wind component of 7 to 9 kt from 10Z-17Z Thu. KBUR...Moderate confidence in TAF. Cigs may arrive linger until as least as 21Z today. && .MARINE...23/542 AM. In the Outer Waters, moderate confidence in the forecast. Winds will be close to low-end Small Craft Advisory (SCA) levels at times thru Fri night. SCA conds are likely (70% chance) in the northern zone (PZZ670) this afternoon thru late tonight, while there is a 40% chance of SCA level winds elsewhere. There is a 40% chance of low end SCA level winds anywhere across the outer waters Thu afternoon thru Fri night/Sat morning. SCA level conds are likely (70% chance) Sat afternoon thru Sun night. For the Inner Waters north of Pt. Sal, moderate confidence in the forecast. There is a 40% chance of SCA level winds during the afternoon/eve hours today thru Fri. SCA conds are likely (60% chance) during the afternoon/eve hours Sat and Sun. For the Inner Waters south of Pt. Conception, moderate confidence in the forecast. There is a 40% chance of SCA level winds during the afternoon/eve hours today thru Fri in western portions of the Santa Barbara Channel, then SCA conds are likely there (60% chance) during the afternoon/eve hours Sat and Sun. Otherwise, SCA conds are not expected thru Sun night. && .LOX WATCHES/WARNINGS/ADVISORIES... CA...Wind Advisory in effect from noon today to 9 PM PDT this evening for zone 381. (See LAXNPWLOX). PZ...Small Craft Advisory in effect from 3 PM this afternoon to 3 AM PDT Thursday for zone 670. (See LAXMWWLOX). && $$ PUBLIC...Hall AVIATION...DB MARINE...DB SYNOPSIS...Hall weather.gov/losangeles Experimental Graphical Hazardous Weather Outlook at: https://www.weather.gov/erh/ghwo?wfo=lox |
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