FXUS66 KLOX 041232 AFDLOX Area Forecast Discussion National Weather Service Los Angeles/Oxnard CA 532 AM PDT Fri Oct 4 2024 .SYNOPSIS...04/352 AM. Slightly cooler temperatures expected today, followed by a heatwave this weekend. Dangerously warm to hot conditions will occur this weekend through Monday across the mountains, valleys, and inland coastal plains. Skies will be clear through the forecast period except for night through morning low clouds and possible dense fog along the coast. && .SHORT TERM (TDY-SUN)...04/531 AM. The marine layer has deepened a bit in response to some height falls across the region, and was now running around 1500 ft deep or so. Onshore gradients have increased slightly. Low clouds were widespread in all coastal areas, and have pushed into a fair portion of the valleys. Some mid and high clouds were drifting into western portions of the forecast area, and believe it or not, a sprinkle or two is not out of the question, mainly from Ventura County northward early this morning. Expect skies to clear by mid morning in the valleys and noon across most of the coastal plain, though some low clouds could linger into the afternoon at the beaches. Heights will begin to rebound this afternoon as a large upper high over the Four Corners are begins to strengthen and expand into the region. However, 950 mb temps will be slightly lower than they were on Thu, and onshore gradients will be slightly stronger. Overall, expect a couple of degrees of cooling in most area today, but the warmest locations in the San Fernando Valley and the Antelope Valley will still have high near 100 degrees today, about 15 degrees above normal for early October. The upper high will drift westward tonight and Sat, becoming centered over southern California. It will then move little Sat night and early Sun before an upper trough in the eastern Pacific starts to force the high eastward late Sun. Heights will rise across the region later today and tonight, which will cause the marine layer to become more shallow. Pressure gradients will become neutral or slightly offshore by Sat morning, then only turn very weakly onshore in the afternoon, and this pattern will be repeated on Sun. With rising heights and a few degrees of warming at 950 mb, expect several degrees of warming in most areas Sat, with little change or even possibly slight additional warming Sun. As a result, it will become dangerously hot away from the coastal plain. Max temps will rise well into the 90s to around or possibly slightly above 105 degrees in the valleys, foothills and lower mountain locations both days. Have upgraded Excessive Heat Watches to Warnings for these locations. It will be very hot including in very popular places for hiking and biking such as the Santa Monica Mountain. People planning even moderately strenuous outdoor activities this weekend should be aware that temperatures will rise quickly as one moves inland from the coast and up in elevation. Strenuous activities should be postponed if possible, or shifted to the early morning or evening hours. Heat Advisories may be needed for the weekend for interior portions of the coastal plain including Downtown Los Angeles, and in the Santa Ynez Valley. .LONG TERM (MON-THU)...04/527 AM. An upper trough in the eastern Pacific will slowly move toward the West Coast Sun night/Mon. Heights will begin to fall, and though gradients will start off neutral, they will turn more strongly onshore in the afternoon. Night thru morning low clouds and fog will likely remain confined to the coastal plain Sun night/Mon morning, but they will probably spread farther inland. Max temps should be down a few degrees in most areas, though they should still be significantly above normal. In fact, there is a chance that Heat Advisories may be needed for many of the same areas under Excessive Heat Warnings this weekend. The trough will sharpen as it move into the West Coast Mon night and Tue, pinching off into a closed upper lower just off the coast of SoCal by late Tue. The marine layer should deepen, with night thru morning low clouds likely pushing into the valleys. Expect several degrees of cooling in most areas on Tue. The upper low will meander across the region Tue night and Wed, likely bringing some additional cooling, along with extensive night thru morning low clouds/fog. There could even be some local morning drizzle. The upper low will drift well to the southeast of the region by Thu but a large trough will move into the eastern Pacific. Even though heights across the forecast area will rise a bit, onshore gradients will increase. In general, expect the cooling trend to continue Thu, though max temps may still be slightly above normal. && .AVIATION...04/1218Z. Due to a data outage, current marine layer and inversion height data is not available for KLAX. High confidence in TAFs for KPRB, KWJF, and KPMD. Moderate confidence in KBUR and KVNY. There is a 20% chance of LIFR to IFR cigs developing until 16Z, and then again tomorrow night. Low confidence in remainder of TAFs. VSBYs may vary between categories from VLIFR to low IFR through 17Z this morning. Cloud clearing times may be off by +/- 90 minutes. KLAX...Low confidence in TAF. VSBY is likely to vary between 2SM to 5SM throughout 18Z. The timing clearing of low clouds could differ by +/- 90 minutes. There is a 20% chance of an east wind component reaching 8 kts until 16Z. KBUR...Moderate confidence in TAF. There is a 20% chance of LIFR to IFR cigs developing until 16Z, and then again tomorrow night. && .MARINE...04/405 AM. For the Outer Waters (along the Central Coast south to San Nicolas Island), moderate to high confidence in the current forecast through Saturday as below SCA (Small Craft Advisory) levels are expected. For Monday through Tuesday, there is a 50-60% chance of SCA level winds, especially in the late afternoon through evening hours. Seas are expected to trend downward today and stay below SCA levels until Monday night, then they are likely to build again to SCA levels through at least mid next week. For the Inner Waters north of Point Sal, moderate confidence in current forecast. Through Sunday, high confidence in winds and seas remaining below SCA levels. For the afternoon and evening hours on Monday and Tuesday, there is a 40-50% chance of SCA level winds. For the Inner Waters south of Point Conception, moderate to high confidence in current forecast. Generally high confidence in winds and seas remaining below SCA levels through Monday. Local NW gusts to 20 kt are possible during the afternoon and evening hours on Sunday around Point Mugu and in the San Pedro Channel. Then, Monday night there is a 20-30% SCA winds for the Santa Barbara Channel. A shallow marine layer will continue to generate some dense fog across portions of the coastal waters the next couple of nights and mornings. Visibilities of one nautical mile or less can be expected. && .LOX WATCHES/WARNINGS/ADVISORIES... CA...Excessive Heat Warning in effect from 10 AM Saturday to 8 PM PDT Monday for zones 38-88-342>345-351>353-356>358-369>376-378>380-548. (See LAXNPWLOX). PZ...NONE. && $$ PUBLIC...DB AVIATION...Schoenfeld MARINE...Schoenfeld/Black SYNOPSIS...RS weather.gov/losangeles Experimental Graphical Hazardous Weather Outlook at: https://www.weather.gov/erh/ghwo?wfo=lox