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Area Forecast Discussion
Issued by NWS Los Angeles, CA
Issued by NWS Los Angeles, CA
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717 FXUS66 KLOX 130336 AAA AFDLOX Area Forecast Discussion...UPDATED National Weather Service Los Angeles/Oxnard CA 836 PM PDT Fri Jul 12 2024 .SYNOPSIS...12/109 PM. The long-lasting heatwave will continue across the mountains and interior areas through Saturday as high pressure remains anchored over the region. The high will weaken over the weekend into early next week, causing a gradual cooling trend through the middle of next week. In the meantime, temperatures inland will remain above normal. Another warming trend will develop later next week and continue into next weekend. && .SHORT TERM (FRI-MON)...12/835 PM. ***UPDATE*** There was a strong and low marine inversion early this evening at around 900 ft deep. Low clouds were extensive along the coast and will push inland overnight and into some of the adjacent vlys. Patchy dense fog was noted along the Central Coast already, with patchy dense fog not out of the question developing for some coastal areas S of Point Conception overnight especially along the SBA County S coast. Otherwise and elsewhere, partly to mostly cloudy skies overall can be expected as more mid-level moisture moves into the area from the SE. There will also be a small chance (less than 15%) of widely scattered showers and a 5-10% chance of a thunderstorm. The chances of these are low enough to not be reflected in the forecast. However, the NAM continued to show the possibility of showers with a slight chance of thunderstorms all day Sat into Sat evening especially for interior areas. Have updated the zones to reflect this change. Any thunderstorms that develop would be capable of producing brief heavy rain, isolated to widely scattered dry lightning and strong, gusty and erratic winds. Gusty SW-NW winds 15 to 25 mph with some gusts up to 30 mph will persist this evening for the foothills, mtns and across the Antelope Vly, but will diminish overnight. It will be warm again tonight for the foothills, lower mtns and deserts, with lows in the 70s to lower 80s expected. These warm overnight lows will give little relief to the ongoing heat wave for interior areas. ***From Previous Discussion*** Strengthening onshore flow along with a deeper marine layer are helping to bring cooler temperatures to inland areas today. The marine layer jumped up to 2000 feet across LA County sloping to around 1500 feet along the Central Coast. Probably won`t see too much change in the marine layer depth tonight an Saturday but the inland cooling will continue as the upper high weakens and the lower levels cool. Ironically, we may see a slight bump in coast/valley temperatures over the weekend as onshore flow weakens by 2-3mb. The temperature rises won`t be excessive and should not jump into the advisory/warning level. The one caveat there is the models are indicating increasing moisture aloft with the southeast flow, likely increasing cloud coverage. So that could at least partially offset the impacts of the offshore trends. Of greater impact is the increase in thunderstorm chances across the interior through Saturday. Already seeing significant mid and high level cloud coverage across LA/Ventura Counties today and models indicate higher PW`s tomorrow and ample instability, albeit at or above 700mb. The high based aspect to it means the chances for dry lightning are greater which posed a significant impact to firefighters tackling the ongoing fires in the area. Any precip reaching the ground would likely be pretty minimal in most cases, but with particularly strong storms with strong updrafts it`s possible that isolated pockets of heavy rain could develop across the mountains and interior areas. Also, can`t rule out possible overnight showers tonight, though chances are too low to include in the official forecast and most of the hi res models hold off until at least mid morning Saturday. Given the current flow pattern PW`s drop off towards the west and north so our western counties would have a higher chance of dry lightning than the eastern counties. Models showing the moisture shifting north and east of the area Sunday and Monday but not totally sold on that. .LONG TERM (TUE-FRI)...12/155 PM. The upper high that has been causing the extreme heat for so long is starting to weaken and shift slightly east. And early next week there will be an onshore trend that will continue the cooling trend until around Wednesday. As the high shifts east and a weak upper low develops off the coast of northern California the flow aloft will take on more of a westerly component which basically will put an end to any thunderstorm chances. For the latter half of the week, high pressure is expected to return from the east bringing warming temperatures to mainly inland areas. Based on the current ensemble solutions, high temperatures should stay below advisory/warning levels through at least Friday with highs 4-8 degrees above normal. However, the warming trend will continue through next weekend and there`s at least a 30-40% chance of 110 or higher across the Antelope Valley and interior SLO County so chances for advisory or warning level heat are increasing during that time. Not seeing any significant offshore trends during that time, so while the warmest coastal valleys will likely be in the 100-105 range, coastal areas should remain mostly in the 70s. && .AVIATION...13/0012Z. At 23Z at KLAX, the marine layer was 1200 feet deep. The top of the inversion was at 5100 feet with a temperature of 30 deg C. Moderate confidence in TAFs for KPRB, KPMD, and KWJF. For these sites, there is a 10% chance for thunderstorms thru tonight and a 20% chance for thunderstorms Saturday afternoon. Thunderstorms will be capable of producing gusty, erratic winds. Moderate confidence in TAFs for KBUR and KVNY. There is a 30% chance that flight categories remain MVFR-VFR thru the period. Moderate to Low confidence in remaining TAFs. For these locations, MVFR to LIFR conditions will return tonight thru Saturday morning. 10-30% chance of VLIFR conditions possible, with the highest chances being at KSBP, KSMX, KSBA, and KOXR. Smoke will further contribute to vsby restrictions, especially at KSBA and sites north of there. The timing of flight category changes may vary +/- 2-3 hours from current forecasts. There is up to a 30% chance for minimum vsbys/cigs to be off by a category. KLAX...Moderate confidence in TAF. Flight categories should remain IFR-LIFR for most of the night, with a 20% chance of VLIFR conditions between 05Z and 15Z. Cigs/vsbys should improve to at least MVFR conditions by 20Z. Flight category change may vary +/- 2 hours from current forecast. No significant east wind component is expected. KBUR...Moderate confidence in TAF. There is a 30% chance that flight categories remain MVFR-VFR thru the period. && .MARINE...12/204 PM. Small Craft Advisory (SCA) conditions are generally not expected through the middle of next week. However, there is a 20% chance of SCA winds in the Outer Waters and far western portions of the Santa Barbara Channel during the late afternoon through overnight hours Monday and Tuesday Dense fog will continue across the coastal waters tonight and Saturday morning. Please reference the Marine Weather Statement for additional information. && .LOX WATCHES/WARNINGS/ADVISORIES... CA...Excessive Heat Warning remains in effect until 9 PM PDT Saturday for zones 38-343>345-353-376>379-381>383. (See LAXNPWLOX). Fire Weather Watch in effect from Saturday morning through Saturday evening for zones 342>345-348-351>353-376>383. (See LAXRFWLOX). PZ...NONE. && $$ PUBLIC...MW/Sirard AVIATION...Lewis/Sirard/Cohen MARINE...Cohen SYNOPSIS...MW weather.gov/losangeles Experimental Graphical Hazardous Weather Outlook at: https://www.weather.gov/erh/ghwo?wfo=lox