FXUS66 KLOX 031856 AFDLOX Area Forecast Discussion...UPDATED National Weather Service Los Angeles/Oxnard CA 1156 AM PDT Tue Sep 3 2024 .SYNOPSIS...03/908 AM. Warm weather today will be followed by a dangerous heatwave for Tuesday through at least Friday. Patchy low clouds and fog will be possible at the coast overnight and into the mornings, otherwise sunny skies will continue. Temperatures will start to trend downwards for the weekend, however even Sunday will be several degrees above normal. && .SHORT TERM (TDY-THU)...03/916 AM. ***UPDATE*** No significant updates at this time. However, a few changes may be forthcoming with the afternoon update just to refine some of the temperatures and also there may be a need to add a couple areas to the existing heat warnings, most notably the Palos Verdes Hills and possibly some of the Central Coast where temperatures could get into the mid to upper 90s. ***From Previous Discussion*** A 1000 ft marine layer and weak onshore flow has brought low clouds to many beaches this morning. But the clouds will not make much of an inland push due to the weak onshore push. The low clouds will not last long and skies will be sunny by mid morning. At the upper levels an upper high will build in over Srn Ca and hgts will climb to 591 dam. These hgts are 4 dam greater than normal and will combine with the weak onshore flow to produce 3 to 6 degrees of warming. Most areas away from the coasts will see max temps between 95 and 105 degrees. The western San Fernando Vly area will be even hotter with max temps between 105 and 109 degrees. An excessive heat warning starts today for this area. Wednesday will see a similar marine layer pattern. The real story, however, will be the heat. With even weaker (almost neutral) onshore flow and hgts climbing to 594 dam under a strengthening upper high, max temps will climb another 2 to 4 degrees. This warming will along with warmer than normal overnight lows will produce excessive heat conditions across the entire area minus the coasts (which will still be 3 to 6 degrees abv normal) The Excessive Heat Warnings go into effect for this entire area late Wednesday morning. Please see the product LAXNPWLOX for all of the details. If the marine layer depth shrinks to under 600 ft the Palos Verdes area would also likely need a heat advisory. On Thursday the gradients go slightly offshore. There will be very little in the way of morning low clouds. Hgts may tick up a dam. This will be the warmest day with temperatures away from the coasts ranging from 100 to 110 degrees with the warmer exception of the western San Fernando Vly which will see kiln-like temperatures near 113 degrees. The offshore flow will bring 3 to 6 locally 8 degrees of warming to the coasts and there is a 40 to 50 percent chc that heat advisories will be needed for the coastal sections. Overnight lows across the vlys and the interior will be very warm and will offer little relief from the heat. Many interior areas will only see low in the 70s and isolated hot spots will not fall below 80. Sundowner winds across the SW Santa Barbara County coast are expected to occur each night, and will likely be strongest Thursday night when N-S gradients are the greatest. Excessively hot conditions and low humidities will make for fire weather concerns. Please see fire discussion for more details. .LONG TERM (FRI-MON)...03/329 AM. On Friday the upper high will weaken slightly and the gradients will trend onshore. Minimal marine layer clouds will continue. There will be some cooling but only 2 to 3 degrees which is no where enough to eliminate the dangerous heat conditions and the excessive heat warnings will continue through the day. The upper high will slowly be pushed to the east by a large Gulf of Alaska upper low that is moving to the PAC NW. By next Monday hgts will fall to near 585 dam. Onshore flow will increase slightly each day. Max temps will fall 3 to 6 degrees on Saturday which should be enough to end the heat warnings (although a few advisories may be need for a few mtn and interior sections). There will be 2 to 4 degrees of additional cooling Sun and Mon. By Monday max temps will come in 2 degrees either side of normal. Near advisory level Sundowner winds will continue Friday evening across the SW Santa Barbara County coast. A 10 percent chance of afternoon thunderstorms remains for the northeastern portion of Los Angeles County Friday through Sunday as some monsoon moisture advection is possible at the mid levels. This low chc is too low to mention in the official forecast. && .AVIATION...03/1853Z. At 1817Z at KLAX, the marine layer was 800 feet deep. The top of the inversion was at 2300 feet with a temperature of 30 C. High confidence in TAFs for KPRB, KBUR, KVNY, KPMD, and KWJF. Low cloud and fog will be similar to last night and generally confined to the near coastal areas. Expect categories with IFR to LIFR when cigs form, with a chance of VLIFR at times. There is a 20% chance of no cigs at KSBA, KOXR, and KCMA tonight. KLAX...Moderate confidence in TAF. There is a 20% chance that cigs tonight will arrive as early as 03-04Z this evening. Any east wind component should remain under 5 kts. KBUR...High confidence in TAF. && .MARINE...03/1155 AM. In the Outer Waters, moderate confidence in the forecast. Small Craft Advisory (SCA) level winds dropped off early this morning. There is a 20-30% chance of SCA level winds this afternoon/evening. For southern two zones (PZZ673/676), SCA conds are likely at times (60% chance), from Wed afternoon thru Sun night, though winds may drop below SCA levels each morning. In the northern zone (PZZ670), there is a 30% chance of SCA conds during the late afternoon/eve hours Thu thru Sat. For the nearshore waters off the Central Coast, high confidence in forecast. Winds are likely to remain below SCA level thru Thu morning. Then there is a 20-30% chance of SCA level winds during the afternoon/eve hours Thu thru Sat. In the Santa Barbara Channel, and the inner waters off the L.A. and Orange County coasts, low to moderate confidence in the forecast. In western portions of the Santa Barbara Channel, and from near Anacapa Island to near Malibu, there is a 30% chance of SCA level winds during the late afternoon/eve hours today and Wed, then a 50-60% chance in those areas during the late afternoon/eve hours Thu thru Sat. Patchy dense fog will continue to affect the coastal waters over the next few days, mainly in the night and morning hours. Visibilities of one nautical mile or less are likely at times. && .LOX WATCHES/WARNINGS/ADVISORIES... CA...Excessive Heat Warning in effect from 11 AM Wednesday to 8 PM PDT Friday for zones 38-88-342>345-348-351>353-356>358-368>371-373>383-548. (See LAXNPWLOX). Excessive Heat Warning in effect until 8 PM PDT Friday for zone 372. (See LAXNPWLOX). PZ...NONE. && $$ PUBLIC...MW/Rorke AVIATION...Schoenfeld MARINE...DB/Schoenfeld SYNOPSIS...MW/Schoenfeld weather.gov/losangeles Experimental Graphical Hazardous Weather Outlook at: https://www.weather.gov/erh/ghwo?wfo=lox