Area Forecast Discussion
Issued by NWS Los Angeles, CA
Issued by NWS Los Angeles, CA
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208 FXUS66 KLOX 060427 AFDLOX Area Forecast Discussion National Weather Service Los Angeles/Oxnard CA 927 PM PDT Fri Jul 5 2024 .SYNOPSIS...05/857 PM. A long-lasting and extreme heatwave will continue across the region, and especially the interior, through much of next week. There is a high risk for dangerous heat illness and fast-growing fires. High temperatures will reach 95 to 105 degrees in many areas away from the coast, and 105 to 115 across interior valleys and mountains. All-time records will be threatened. Dense fog may develop across some beaches during the night and morning hours. && .SHORT TERM (TDY-MON)...05/927 PM. ***UPDATE*** There were some impressive high temperatures today from SLO County to LA County, perhaps the most notable being Saugus at 118. Official temperature records are kept there so it`s unknown if that was an all-time record or not. In fact, the entire Santa Clarita Valley was exceptionally hot today as the entire valley was anywhere from 112-118. The expected northerly flow did develop earlier today and that was certainly a contributing factor there. Farther south in the San Fernando Valley temperatures were hot as well but not close to the what the Santa Clarita Valley experienced, likely because the northerly flow just didn`t reach down that far in elevation, though in the Chatsworth area highs did reach around 109, and 106 at Woodland Hills Pierce College. Still monitoring the northerly flow this evening across the Santa Ynez Range down into the south coast areas. It`s still quite hot in the foothills with temperatures around 100 at 9pm at 1500 feet elevation on San Marcos Pass and throughout all the coastal foothills there. Could still see some of that heat filter down towards the coast over the next few hours but it looks like for the most part it will stay elevated. 00z models continue to indicate significant cooling at lower elevations tomorrow and again Sunday with a strong onshore trend in the afternoon. Most valley areas expected to cool by 3-6 degrees Saturday, which still keeps most of those areas high 90s to around 105. With a reversal of the low level from north to south Saturday, places like the Santa Clarita Valley should see even more cooling, but should still top out in the 100-110 range. So despite the cooling, it should be emphasized that these temperatures are still extremely hazardous to those outdoors. Additional cooling expected Sunday and based on the heat risk calculations most of the coast and coastal valleys may be at a much lower risk level by Sunday. Some consideration may have to given to possibly ending the heat hazards on Saturday based on the current forecast for Sunday. However, a warming trend is expected again early next week as onshore flow weakens so there are still some very hot days in the near future. ***From Previous Discussion*** The long lasting and extreme heat wave continues, peaking through Saturday. This is a dangerous situation with all the ingredients for a high risk of heat-illness and fast growing fires. PLEASE avoid hiking in the mountains and the hills through this weekend, make plans on how you will stay cool in the afternoon and evening hours, and stay away from anything that could spark a fire. A 595-98 decameter upper level high pressure system will dominant the west coast through most of next week. The high is currently centered over northwest California, which is in a position favorable for causing the near neutral onshore pressure gradients that we saw today, and the shift to northerly for the north-to- south gradients. Any of those three ingredients alone would heat things up, but when they all happen together we are in extreme territory. Many valley and mountain areas are already near to or exceeding 100 degrees, with the Santa Clarita Valley hovering around 115 (no official records available for that location). The extreme heat is also causing a deep mixing/boundary layer which has allowed for some fair weather cumulus clouds over the mountains but will not be a convection threat. Near the coast, a shallow but persistent marine layer remains, and does not look to be going anywhere. As a result, the immediate coastal areas will be closer to mild than hot, but the temperatures will ramp up quickly for every mile inland of the beach. With the shallow marine layer, dense fog will remain a concern especially with the lingering smoke particles in the air from all the firework activity. The high will gradually slide into southeast California through Monday. As a result, the northerly shift in the flow from today will transition to more onshore Saturday afternoon through Sunday or Monday. On the COASTAL side of the mountain ranges, this shift will bring a much earlier than usual daytime peak in temperatures (closer to 10am than the afternoon) as a less hot air mass over the ocean pushes in. While it will still be hot Saturday and Sunday, will not be as hot as today and the trends should be going down. The marine layer should also expand a little as well. As a result, decided to pull the end time of the Heat Warnings and Advisories back a day to Saturday or Sunday (depending on your location)...and they back need to all be pulled back to Saturday. Over the INTERIOR mountains and valleys/deserts, this shift will do very little. In fact, with the shift of the core of the high moving closer, Saturday very well could be the hottest day of the event for the furthest interior areas, with Sunday still hot but down a few degrees with the peak of the onshore flow. As such, did not touch the Heat Warnings for those locations. Many calendar day records are expected to be broken today. All-time records (for any calendar day) could break on Saturday at Palmdale, Lancaster and Paso Robles. .LONG TERM (TUE-FRI)...05/213 PM. The upper level high, centered over southeast California on Monday, is poised to meander northwest into Nevada Tuesday through at least Thursday. This will cause the strength of high pressure over southwest California to drop a bit, resulting in a few degrees drop in the temperatures over the mountains and interior (still very hot). This will also cause the onshore flow to weaken once again (similar to today but likely not to this magnitude). As a result, coastal and valley areas will likely trend hotter again. While there is a range in the ensemble projections, most push temperatures inland of the beaches back up to about 5 degree below today and tomorrows temperatures. On top of that, northwest winds will increase, especially over southwest Santa Barbara County, which will further warm it up. So the morale of the story is that this heat wave may not be done with us just quite yet. && .AVIATION...06/0023Z. At 00Z at KLAX, the marine layer was 900 feet deep. The top of the inversion was at 3200 feet with a temperature of 37 deg C. High confidence in 00Z CAVU TAFs for KPRB, KBUR, KVNY, KPMD, and KWJF. Moderate confidence in the rest of the coastal 00Z TAFs. There is a 30% chance that KSBP reaches IFR conditions due to uncertainty of cig/vsby arrival. There is a 20% KSMX remains MVFR throughout the forecast period. All other coastal sites should reach IFR/LIFR conditions tonight, clearing around midday. Arrival and dissipation of cigs/vsbys may be off +/- 2 hours. KLAX...Moderate confidence in the 00Z TAF. There is a 30% chance that cigs may arrive as early as 04Z. There is a 20% that VLIFR conditions may occur in the period after 10Z through 14Z. Cigs/vsbys are expected to improve to at least MVFR conditions around 15Z. No significant easterly component of the wind expected in the forecast period. Arrival and disspation of cigs/vsbys may be off +/- 2 hours. KBUR...High confidence in the 00Z TAF. VFR conditions should prevail for most of the forecast period. However, there is a 10-20% chance of MVFR conditions due to decreased vsbys in the morning. && .MARINE...05/803 PM. In the Outer Waters, Small Craft Advisory (SCA) level winds will continue in the southern zones (PZZ673/PZZ676) thru Sat morning. In the northern zone (PZZ670), SCA conds are likely (70% chance) this afternoon thru Sat morning. For the most part, expect winds to remain below SCA levels Sat afternoon thru Wed night except for a 50% chance of SCA level wind gusts at times Sunday night. There is also a 30% chance of SCA level NW winds in the far outer waters and from near Pt. Conception to NW of San Nicolas Island, especially during the late afternoon thru late evening hours. For the Inner Waters N of Pt. Sal, conditions have subsided below SCA levels. There is a 30% chance of SCA level winds Sat afternoon/eve, otherwise SCA conds are not expected Sat night thru Wed night. For the inner waters south of Pt Conception, SCA conditions are not expected through Monday. SCA winds will be possible Tuesday evening in western portions of the Santa Barbara Channel, mainly from Santa Cruz Island to the SBA County south coast from Pt. Conception to Gaviota to Refugio State Beach. Otherwise, conds will be below SCA levels for the southern inner waters thru Wed night. Areas of dense fog will affect portions of the coastal waters tonight into Sat morning. Please reference the Marine Weather Statement for additional information. && .BEACHES...05/115 PM. A moderate southerly swell will affect the Southern California coastal waters through Sunday, with a 15-17-second period this weekend. While surf is not expected to be particularly high, surf heights of up to 4 to 6 feet are anticipated at beaches exposed to southerly swell, especially the LA and Ventura County beaches. The significant wave energy with the long-period swell will combine with the elevated surf to create dangerous conditions at area beaches, with powerful and dangerous rip currents expected. This is especially the case for the south-facing beaches of LA and Ventura Counties. A Beach Hazards Statement is in effect through the weekend to address these concerns. && .LOX WATCHES/WARNINGS/ADVISORIES... CA...Excessive Heat Warning now in effect until 9 PM PDT Wednesday for zones 38-343>345-353-376>379-381>383. (See LAXNPWLOX). Excessive Heat Warning now in effect until 9 PM PDT Sunday for zones 88-342-348-351-352-356>358-369>375-380. (See LAXNPWLOX). Heat Advisory now in effect until 9 PM PDT Saturday for zones 341-347-355-367-368. (See LAXNPWLOX). Excessive Heat Warning now in effect until 9 PM PDT Saturday for zones 349-350. (See LAXNPWLOX). Wind Advisory remains in effect until 3 AM PDT Saturday for zones 349-351. (See LAXNPWLOX). Beach Hazards Statement in effect through Sunday evening for zones 354-362-366. (See LAXCFWLOX). Heat Advisory now in effect until 9 PM PDT Sunday for zone 548. (See LAXNPWLOX). Red Flag Warning in effect until 6 AM PDT Saturday for zones 342>345-349-351>353-376-377. (See LAXRFWLOX). Red Flag Warning in effect until 6 AM PDT Monday for zones 378-381. (See LAXRFWLOX). PZ...Small Craft Advisory in effect until 3 AM PDT Saturday for zones 645-670. (See LAXMWWLOX). Small Craft Advisory in effect until 9 AM PDT Saturday for zones 673-676. (See LAXMWWLOX). && $$ PUBLIC...MW/Kittell AVIATION...Lewis MARINE...Sirard/Lewis/Smith BEACHES...Sirard SYNOPSIS...MW weather.gov/losangeles Experimental Graphical Hazardous Weather Outlook at: https://www.weather.gov/erh/ghwo?wfo=lox