Area Forecast Discussion
Issued by NWS Los Angeles, CA
Issued by NWS Los Angeles, CA
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567 FXUS66 KLOX 311756 AAA AFDLOX Area Forecast Discussion...UPDATED National Weather Service Los Angeles/Oxnard CA 1056 AM PDT Fri May 31 2024 .SYNOPSIS...31/903 AM. A cooler than normal weather pattern will continue across much of the area through the weekend as a persistent marine layer remains in place with strong onshore flow. A warming trend is expected next week, especially for the interior portions of the area Wednesday and Thursday as onshore flow weakens. && .SHORT TERM (TDY-SUN)...31/908 AM. ***UPDATE*** The marine layer has deepened by around 500 feet compared to yesterday and clouds have responded by pushing farther inland and higher up the coastal mountain slopes. Onshore gradients are stronger as well so all signs are pointing towards a cooler day for coast and coastal valleys with slower (if any) clearing of low clouds. Farther inland across the mountains and interior areas it will sunny and warm with highs in the upper 80s to mid 90s with some breezy late afternoon winds. ***From Previous Discussion*** The latest local 3-km WRF time height sections suggest the marine layer deepening additionally tonight into Saturday morning, and Saturday night into Sunday morning as broader troughing aloft will reinforce strong onshore flow. As the latest model solutions have not handled the modeling of the marine layer depth well, the forecast trends a little more aggressive with the low cloud field over the coming days. Weak omega values in the mixed layer in the latest 3-km local WRF solutions suggest the threat of drizzle could be higher over the next couple of mornings, but high- resolution multi-model ensemble solutions downplay the drizzle threat to some extent. Considering there are a few locales with drizzle this morning, the forecast may need to lean more toward the deterministic solution of the local 3-km WRF. Future shifts may need to add drizzle mentions to the forecast for Saturday morning and again for Sunday morning if this signature continues into the coming model runs. With strong onshore flow in place and strengthening additionally today, a cooling trend will develop through the weekend as clouds will struggle to clear from the land mass each day. The forecast goes with clouds hugging the beaches and immediate coast each day, but with KLAX-KDAG surface pressure gradients progged to approach 8 mb onshore, there is a moderate chance that clouds may linger longer across some interior coast and valleys today. Marginally gusty winds will develop across the interior valleys, such as the Antelope Valley and adjacent foothills each afternoon and evening. The latest forecast guidance suggest winds increasing to near advisory levels, but the forecast holds off on issuing any advisories at this point to wait for more data. The latest NAM-WRF solutions trend closer to advisory level winds developing across the Antelope Valley foothills on Saturday afternoon and evening, but the latest forecast ensemble members still lean toward the winds being more on the marginal side. .LONG TERM (MON-THU)...31/450 AM. A warming trend will establish on Monday as high pressure aloft starts to build in over the region. A developing northerly surface pressure gradient will develop gusty northerly winds, most likely affecting the Interstate 5 Corridor on Monday night into Tuesday. EPS solutions bring wind gust means to near 50 mph at KSDB, likely producing the strongest winds at sites like Whitaker Peak and Poppy Park. Gusty Sundowner winds cannot be ruled out either as pattern recognition in some of the deterministic solutions suggest a wind event could develop across southern Santa Barbara County. EPS ensemble members continue to suggest a warming trend turning more significant for Wednesday and Thursday as a cutoff upper- level trough sits south of the border off the Baja California coast and ridging aloft noses into southeast California. Confidence is high for a hot weather pattern developing away from the coast but lower for the coastal areas due to the persistence of onshore flow. NBM solutions give about an 80 percent chance of KPMD and KWJF hitting 100 degrees for the first time this year. Temperatures break away from NBM solutions, going warmer for the middle portion of next week across the interior portions of the area. && .AVIATION...31/1755Z. At 17Z at KLAX, the marine layer was 2500 ft deep. The top of the inversion was at 3800 feet with a temperature of 19 deg C. Moderate to hi confidence in the 18Z TAFs. Low clouds over the coast and adjacent vlys will clear to near the coast by late this morning, with MVFR conds likely persisting thru the afternoon at KOXR, KCMA, KSMO and KLAX. IFR/MVFR cigs will likely spread back inland tonight and affect all coast and adjacent vly airfields and continue into late Sat morning. The timing of the dissipation and onset of low clouds may be off +/- an hour or two, with the largest uncertainty of the onset of low clouds tonight for KBUR and KVNY. For KPRB, KWJF and KPMD, there is hi confidence VFR conds will continue thru the TAF period. Gusty SW winds will affect the desert airfields for most of the fcst period. KLAX...Moderate to hi confidence in the 18Z TAF. MVFR cigs will likely persist this afternoon with only a 20% chance of the low clouds scattering out. There is a 50% chance of IFR cigs early this evening, otherwise MVFR cigs will continue tonight thru Sat afternoon. No significant east wind expected. KBUR...Moderate to hi confidence in the 18Z TAF. VFR conds are expected for the most part into this evening, then IFR cigs should move in by 07Z. The cigs will improve to MVFR by 11Z and continue into late Sat morning. The timing of the onset of the low clouds and changes in flight cats tonight may be off +/- an hour or two. && .MARINE...31/849 AM. In the northern outer waters zone (PZZ670), winds and seas are expected to reach Small Craft Advisory (SCA) levels (80% chance) this afternoon thru early Sat afternoon. Elsewhere in the outer waters, winds and seas are expected to remain below SCA levels thru early Sat afternoon, with just a 20% chance of SCA level gusts in the central zone (PZZ673) this afternoon and evening. There is a 50% chance of gales in the northern zones (PZZ670/673) Sat afternoon thru Sun night. A Gale Watch has been issued. SCA level winds are likely (70% chance) in the southern zone (PZZ676) Sat afternoon thru Sun night, with just a 20% chance of gales. SCA conds are likely (70% chance) in the outer waters Mon-Tue. In the inner waters N of Pt. Sal, there is a 30% chance of SCA level winds this afternoon/evening. SCA conds are likely (60-70% chance) during the afternoon/eve hours Sat thru Mon. In the inner waters S of Pt. Sal, there is a 40% chance of SCA winds in western portion of the SBA Channel Sat afternoon/eve. SCA level winds are likely there (60-70% chance) Sun afternoon/eve. Otherwise, SCA conds are not expected. && .LOX WATCHES/WARNINGS/ADVISORIES... CA...NONE. PZ...Small Craft Advisory in effect from 3 PM this afternoon to 3 PM PDT Saturday for zone 670. (See LAXMWWLOX). Gale Watch in effect from Saturday afternoon through late Sunday night for zones 670-673. (See LAXMWWLOX). && $$ PUBLIC...MW/Hall AVIATION...Sirard MARINE...DB/Sirard SYNOPSIS...Hall weather.gov/losangeles Experimental Graphical Hazardous Weather Outlook at: https://www.weather.gov/erh/ghwo?wfo=lox