FXUS66 KLOX 290559 AFDLOX Area Forecast Discussion National Weather Service Los Angeles/Oxnard CA 1059 PM PDT Sat Sep 28 2024 .SYNOPSIS...28/210 PM. A persistent marine layer will keep the coastal areas below normal through Sunday with areas of morning dense fog. Warmer than normal conditions will continue away from the coast through Sunday. A warming trend will develop for early next week as onshore flow will weaken beneath a building ridge of high pressure. Temperatures for Tuesday and Wednesday should warm to much above normal then cool slightly for late next week. && .SHORT TERM (SAT-TUE)...28/905 PM. ***UPDATE*** Atypical late September weather continued this evening with moderate onshore supporting low clouds and fog rushing back into coastal areas with a good shot at reaching some coastal valleys and the Salinas Valley. Made minor tweaks to expand low cloud and fog coverage tonight. ***From Previous Discussion*** Low clouds lingered along some of the beaches early this afternoon. Otherwise mostly sunny skies prevailed across the forecast area with little change expected thru the afternoon. Breezy onshore flow will prevail this afternoon, with the highest gusts in the Antelope Vly. Temps this afternoon will range from a few degrees below normal along the coast to 10-15 deg above normal for the interior vlys, mtns and deserts. Highs should reach the 60s to near 70 at the beaches, 70s to near 80 for the inland coast, 80s to mid 90s for the vlys and lower mtns, and 90s to around 100 for the Antelope vly. A weak H5 upper level low (581 dam) was a couple of hundred miles SW of Point Conception this afternoon. This upper level low is forecast to meander NE to the SBA County coast tonight then into northern L.A. County by Sun afternoon before moving little thru Sun night. It should drift S of the area on Mon then dissipate Mon night. Upper level ridging is expected to build into central CA on Tue. The forecast area will be on the southern periphery of this upper level ridging on Tue with H5 heights increasing to around 591 dam. A broad easterly flow aloft can be expected over the region at that time. The marine inversion will shrink to 1000 ft or perhaps slightly lower tonight into Sun morning as pressure gradients trend offshore. Low clouds are still expected to spread along nearly all coastal areas tonight and into many adjacent vlys by late tonight Patchy dense fog will also be possible with any low clouds. For Sun night into Tue morning, low clouds and fog are expected again but there will be much less coverage as pressure gradients and trends turn offshore during the night and morning hours. The immediate Central Coast and L.A. County coast can expect the low clouds Sun night into Mon morning, but then be confined to the L.A. County coast Mon night into Tue morning. Any low clouds will continue to be accompanied by patchy dense fog as the marine inversion shrinks to 600 ft or less. Otherwise, mostly clear skies will cover the forecast area tonight through Tue. Breezy onshore flow is expected afternoon and evening hours, with breezy offshore flow night and morning hours Mon and Tue especially for the foothills including the Santa Lucia Mtns in SLO County. Temps on Sun will continue to be a few degrees below normal for the coast and adjacent vlys and several degrees above normal for the inland vlys, mtns and deserts. Offshore pressure gradients will then help to bring significant warming for Mon and Tue. By Tue afternoon temps will be 10-20 deg above seasonal norms. This combined with overnight lows quite a bit above normal will bring heat concerns to the area. There is a good chance that Heat Advisories or Excessive Heat Watches will eventually need to be issued for Tue mainly for areas away from the coast, altho portions of the Central Coast may also be included. The hottest temps on Tue should be in the 95-105 degree range for much of the vlys, lower mtns and deserts. .LONG TERM (WED-SAT)...28/209 PM. The EC and GFS mean ensembles were is somewhat good agreement for the extended period, with the deterministic showing a few more differences. Overall, the mean ensembles indicate that upper level ridging to some degree will prevail over the forecast area Wed thru Sat, altho the EC is much more pronounced with the ridging. Wednesday should have little change over Tue as weak pressure gradients and upper level ridging will bring another day with much above normal temps and possible heat products. Pressure gradients should turn more onshore for Thu with cooler temps expected altho remaining quite a bit above normal. For Fri and Sat, temps will cool slightly but continue several degrees above normal away from the immediate coast. There is a small chance that some offshore gradients could develop Fri into Sat which could result in even warmer temps than forecast. The marine inversion should remain rather shallow thru the extended period. As far as any night and morning low clouds and fog, they should be minimal Wed, then possibly affect mainly portions of the Central Coast Thu thru Sat. Otherwise, mostly clear skies will continue except for the chance of some high clouds moving in late next week. && .AVIATION...29/0337Z. At 2359Z at KLAX, the marine layer was 800 ft deep. The top of the inversion was at 3000 ft with a temperature of 27C. High confidence in the TAFs for KWJF and KPMD. Low confidence in cigs for KPRB, KBUR and KVNY, and will likely arrive 11Z. Good confidence in cigs for remaining sites, low confidence in timing of flight cat changes. KLAX...Moderate to low confidence in the 00Z TAF, LIFR conditions may fail to develop. No significant east wind component expected. KBUR...High confidence in the 00Z TAF through 07Z, then low confidence. There is a 10% chance for VFR conds thru the period. If cigs arrive, there is a 30% chance for cigs OVC001 and/or vsbys less than 1/2SM between 07Z and 16Z. && .MARINE...28/1059 PM. In the Outer Waters (Central Coast to San Nicolas Island), winds are expected to remain below Small Craft Advisory (SCA) levels, however seas have reached 10 feet at multiple locations for the waters north of the Channel Islands. Therefore, issued SCA for these areas tonight into Sunday night. SCA level winds are likely (60-70% chance) for Sunday afternoon thru late night in all zones. Then, moderate confidence in sub advisory winds Monday thru late Thursday. There is a chance (20-30%) for SCA level winds in the Outer Waters is during the afternoon thru late evening hours Wed and Thurs. For the inner waters north of Pt Sal, moderate to high confidence in winds remaining sub advisory level thru Thurs. However, moderate confidence in SCA level winds tomorrow afternoon thru evening. There is a 10-20% chance of SCA level winds Wed/Thurs afternoon thru evening. For the the Santa Barbara Channel, and inner waters off the LA and OC coasts, moderate to high confidence that winds and seas will remain below SCA levels thru Thurs night. However, SCA level winds are possible in the western and southern portions of the SB Channel Sunday afternoon thru evening, and local gusts to 20 kt may occur from Anacapa Island to Point Dume, and thru the San Pedro Channel. There is a 10-30% chance of SCA level winds in the SB Channel and southern inner waters Wed and Thurs in the afternoon/evening hours, with higher chances Wed. Patchy dense fog with vsbys 1 NM or less will affect the waters thru at least tomorrow morning, most widespread off the Central Coast. && .LOX WATCHES/WARNINGS/ADVISORIES... CA...NONE. PZ...Small Craft Advisory in effect from 3 PM Sunday to midnight PDT Sunday night for zones 645-650. (See LAXMWWLOX). Small Craft Advisory in effect until 3 AM PDT Monday for zones 670-673. (See LAXMWWLOX). Small Craft Advisory in effect from 3 PM Sunday to 3 AM PDT Monday for zone 676. (See LAXMWWLOX). && $$ PUBLIC...Munroe/Sirard AVIATION...Phillips MARINE...Phillips/Lewis SYNOPSIS...Sirard weather.gov/losangeles Experimental Graphical Hazardous Weather Outlook at: https://www.weather.gov/erh/ghwo?wfo=lox