Area Forecast Discussion
Issued by NWS Los Angeles, CA
Issued by NWS Los Angeles, CA
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401 FXUS66 KLOX 171229 AFDLOX Area Forecast Discussion National Weather Service Los Angeles/Oxnard CA 529 AM PDT Fri May 17 2024 .SYNOPSIS...17/340 AM. A persistent marine layer will remain in place through the weekend as strong onshore flow continues across the area. Night through morning low clouds and fog will continue to be a staple of the forecast, struggling to clear from the coast each afternoon. Breezy to gusty onshore winds will occur across the interior valleys and adjacent foothill areas each afternoon and evening. Better clearing with slight warming is possible next week as onshore flow could weaken. && .SHORT TERM (TDY-SUN)...17/340 AM. The latest fog product imagery continues to show a deep marine layer depth in place over the area. Low clouds and fog have pushed well into the coastal slopes of the mountains and into interior San Luis Obispo County this morning. Clouds are even making their way into the Cuyama Valley. Another day of May Gray is shaping up for today as ridging aloft remains in place with strong onshore flow across the area. Earlier AMDAR soundings from KLAX several hours ago indicated an marine layer depth up to around 2800 feet deep, but with the cloud extent, one would expect the marine layer depth to be closer to 3500 feet deep, and likely shallower along the Central Coast. A cooler weather pattern will persist with clouds struggling to clear from the coast due to strong onshore flow remaining in place. An upper-level trough near 30N and 135W will start to drift toward southern California through the weekend. EPS cloud cover means keep night through morning low clouds and fog well entrenched through at least Monday, and hint at a spillover into the Antelope Valley on Saturday morning. Weak dynamics with the upper-level trough will start to scrape the area tonight and into Saturday morning. The dynamics with the trough will likely lift the marine layer induced cloud deck and squeeze out some drizzle. PoPs were nudged higher tonight through Saturday morning to account for the drizzle possibility. While it is less confident, there is an outside chance that mountains showers could develop on Saturday afternoon and evening, but most model solutions suggest the middle-levels of the atmosphere to be too dry at this time. Strong onshore pressure gradients will likely bring breezy to gusty onshore winds each day across the high valleys and interior portions of the area and into the adjacent foothill areas. Winds appear to remain below advisory levels again today, but winds are expected to increase on Saturday and Sunday. At this time, advisory levels could occur across the Antelope Valley and adjacent foothill areas. A wind advisory may be issued later to account for gusty southwest winds in places, such as Lake Palmdale and Sierra Pelona. At the very least, elevated fire weather conditions will continue across the interior portions of the area, such as the Antelope Valley this afternoon and evening where winds could combine with drier conditions to bring elevated fire weather conditions. .LONG TERM (MON-THU)...17/337 AM. EPS cloud cover means suggest better clearing after Monday as an upper-level trough digs south down the state. Cold air advection moving south with a decaying frontal boundary could transport enough colder air to weaken the marine inversion. Thus, confidence continues to grow for temporary break of May Gray for the early half of next week. GEFS ensemble pressure gradients suggest onshore pressure gradients weakening for Tuesday and Wednesday. The weakening onshore gradients should promote an earlier clearing of the marine layer stratus for the coastal and valley areas. Gusty northerly winds will be possible across southern Santa Barbara County and through the Interstate 5 Corridor during evening and morning hours between Monday night and Wednesday morning. The forecast still takes a conservative approach for next week as there is a spread of the possible outcomes in the forecast ensembles for Tuesday and Wednesday, but if the ensembles continue to trend this direction, the changes to the forecast should occur and a warming trend with less clouds should be expected. && .AVIATION...17/1228Z. At 12Z at KLAX, the marine layer was 3400 ft deep. The top of the inversion was 4300 feet with a temperature of 21 C. Once again, widespread clouds across the entire area early this morning with the exception of the Antelope Valley, most mountain locations and the far interior valleys of SLO/SBA Counties. Conds were mostly MVFR, except locally IFR north of Pt. Conception, and widespread LIFR to VLIFR in the foothills and mtn slopes. There may be slightly faster and more complete clearing today, with skies clearing by noon in the valleys and early afternoon across interior sections of the coastal plain. It will likely stay cloudy at many immediate coastal locations, but cigs should rise into the VFR category. Expect similar conds tonight, with clouds in all coasts, valley and mtn slope areas. Conds will be mostly MVFR, except LIFR to VLIFR in the foothills and mtns. KLAX...Moderate confidence in TAF. There is a 20-30% chance that cigs will linger all day, though they should rise into the VFR category. There is a 20% chance that cigs will arrive as early as 01Z. No significant easterly wind component is expected. KBUR...Moderate to high confidence in TAF. There is a 20-30% chance that cigs tonight will arrive as early as 04Z. && .MARINE...17/335 AM. In the Outer Waters, rather high confidence in the forecast. Small Craft Advisory (SCA) conditions are not expected thru Sun. There is a 30-40% chance of SCA winds/seas in the outer waters Sun night/Mon, and SCA conds are likely Tue. For the Inner Waters N of Pt. Sal, high forecast confidence. Winds and seas are expected to remain below SCA levels thru Mon night, with a 20-30% chance of SCA winds Tue. In the Inner Waters S of Pt. Conception, moderate to high forecast confidence. There is a 20-30% chance of SCA level winds in western portions of the SBA Channel in late afternoon/eve hours Mon and Tue. Otherwise, SCA conds are not expected. && .LOX WATCHES/WARNINGS/ADVISORIES... CA...NONE. PZ...NONE. && $$ 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