Area Forecast Discussion
Issued by NWS Los Angeles, CA
Issued by NWS Los Angeles, CA
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990 FXUS66 KLOX 181724 AFDLOX Area Forecast Discussion...UPDATED National Weather Service Los Angeles/Oxnard CA 1024 AM PDT Tue Jun 18 2024 .SYNOPSIS...18/1022 AM. A brief warm-up with dry weather will occur today outside of the marine influence, but near normal temperatures will continue across the coastal areas. Slightly below normal temperatures Wednesday and Thursday, followed by a warming trend away from the coast through the weekend. && .SHORT TERM (TDY-THU)...18/1016 AM. A fairly complex pattern exists this morning across the area as a battle is being waged across the area between onshore and offshore flow. An eddy circulation remains intact just south of Catalina Island currently. A pretty good extent of low clouds pushed into the Los Angeles County coast and valleys this morning, despite onshore pressure gradients weakening substantially. The marine layer depth remained wedged in across the area, continuing to resist the offshore push. Outside of the marine influence, marginally gusty offshore winds remain at this time across the Los Angeles County mountains. The wind advisory will likely be allowed to expire at 11 am this morning. A drier air mass will push down into the foothills, mountains, and higher valleys today as the offshore push filter down into these area. Consequently, warmer conditions are expected across these locations as the offshore influence weighs more heavily into the forecast today. Thus, warmer, drier, and marginally windy conditions will continue to develop less than ideal fire weather conditions across the foothills, mountains, and higher valleys through at least tonight. Very minor changes are expected over the next 24 to 36 hours. 500 mb heights and 1000-500 mb thickness values do not change much overhead. The latest NAM-BUFR and local 3-km WRF time height sections suggest the marine layer depth thinning slightly down to about 1800 feet deep at KLAX from 2600 feet deep currently. As a result, clouds should be a little less extensive tonight and into Wednesday morning. Northerly winds occurring the last several nights across southern Santa Barbara County and through Interstate 5 Corridor will become confined to southern Santa Barbara County this afternoon and evening, but marginally gusty winds will likely continue through tonight through Interstate 5 Corridor. A wind advisory will remain in effect for this afternoon and tonight across southern Santa Barbara County. ***From Previous Discussion*** The region will continue to be under a deep broad trough, with heights likely to creep upwards very slowly through Thursday. Overall minimal change to the upper level pattern through the short term period. A brief pulse in the broad trough will allow for a short-lived period of enough cold air advection over the interior to develop cooler temperatures inland compared to at the coasts. This temperature difference is quite unseasonable and is reflected in the pressure gradients. While the LAX to DAG pressure gradient is currently slightly onshore at 2.1 mb, by around 5 AM today it is expected to flip to offshore from the northeast by about 1 mb. The offshore gradient will yield advisory level gusts across the western San Gabriel Mountains and adjacent areas, including the I-5 Cooridor and the Post Fire region. Wind gusts of 30-45 mph will be common, with up to around 50 mph for the highest peaks of the western San Gabriel Mountains. NE flow may extend southward to the Santa Monica mountains, and warm the coastal valleys north of the mountains. Winds are likely to fall below advisory level by late morning, and Wnd Advisories are in effect for the I-5 Cooridor, the Western San Gabriel Mountains, the western Antelope Valley Foothills, and the Santa Clarita Valley through 11 AM today. The currently northwesterly winds will shift to the northeast early this morning and will also continue to support critical fire weather conditions through today (see FIRE WEATHER discussion). The Post Fire burn areas is likely to see a downward trend in winds, however the NW winds will shift to to from the NE in alignment with the San Gabriel Mountains. Smoke from the fire will continue to affect Los Angeles and Ventura Counties today. Please reference the Air Quality Alert Message for additional information. Sundowner NW winds across southern Santa Barbara County are expected redevelop this afternoon into late tonight again for the entire Santa Ynez Range and the western portion of the south coast. Wind gusts of 35 to 45 mph will be common, peaking over the higher elevation. Wind Advisories will go into effect for the aforementioned locations starting at 3 PM today and last until late tonight. Sundowner winds will likely return Wednesay and Thursday evening as well, however there is only around a 30% chance of Wind Advisories being needed, as the N-S surface pressure gradients are expected to trend downward. The offshore flow across the region will lead to an increase in temperatures today. As the LAX to DAG gradient is expected to return to onshore Wednesday, temperatures will cool to a few degrees below normal through Thursday, mostly in the 70s except upper 60s at the beaches and in the 80s and 90s over interior valleys and foothills. In addition, strong northerly flow over the coastal waters is expected to continue, fueled by upper level support and N-S pressure gradients. The nearshore gradient, however, points from south to north and this will turn the winds towards and up the coast forming a persistent Catalina Eddy that will bring marine influence and morning low clouds and fog along the southern coasts. .LONG TERM (FRI-MON)...18/337 AM. On Friday the trough is likely to break down. The GFS and ECMWF both agree that the upper level heights will increase rapidly though Saturday as a strong ridge builds in. Heights of 590-592 dam are expected Sunday and Monday, and strong onshore pressure gradients are likely into early next week. This upper level pattern supports a very shallow marine layer that is likely to cling to the beaches all day. However once out of the marine layer, inland areas will see very warm to hot conditions around 10 degrees above normal. The Antelope Valley is likely to see highs ranging from 100-105 Friday through the weekend, with interior valleys in the mid 90s. At this time, there is around a 10-30% chance of heat-related headlines for the upcoming weekend into early next week. && .AVIATION...18/1219Z. At 1115Z at KLAX, the marine layer was 2200 feet deep. The top of the inversion was at 4400 ft with a temperature of 21 deg C. Good confidence in TAFs for KSBP, KSBP, KPMD, KWJF and KPRB. At KPMD and KWJF, brief restrictions due to BLDU or FU is possible. Moderate confidence in TAFs for KSMO, KLAX, KLGB, KBUR, KVNY and KOXR. There is a 30 percent chc that clearing will occur an hour later than fcst. Moderate Confidence in TAFs for KCMA and KSBA with a 25 percent chc of IFR cigs 14Z-18Z. KLAX...Moderate confidence in TAF. There is a 30 percent chc of clearing delayed until 19Z. Low cloud returns this evening may be as late as 08Z. There is a 10 percent chance of an east wind component of 8 kts between 10-16Z. KBUR...Moderate confidence in TAF. There is a 30 percent chc of clearing delayed until 18Z && .MARINE...18/820 AM. For the Outer Waters, high confidence in current forecast. Small Craft Advisory (SCA) Winds are expected through at least Wednesday night and perhaps as late as Friday. Conditions are expected to be below SCA levels Friday night through Saturday night. For the Inner Waters north of Point Sal, high confidence in current forecast. SCA level winds will persist through at least Wednesday and probably through Thursday night. The winds will be strongest during the afternoons and evenings. For Friday through Saturday night, winds and seas should remain below SCA levels. For the Santa Barbara Channel, moderate confidence in current forecast. Winds will mostly be below SCA levels, but during the afternoons and evenings through Friday there will be local SCA level gusts across the western third of the channel. There is a 30 percent chance that the gusts will be widespread enough to warrant a SCA. South of the SBA Channel, there is a 30% chance for SCA winds Thursday evening. Otherwise, winds and seas will generally be below SCA levels. && .LOX WATCHES/WARNINGS/ADVISORIES... CA...Wind Advisory now in effect until 11 AM PDT this morning for zones 88-378-379-381. (See LAXNPWLOX). Wind Advisory in effect until 11 AM PDT this morning for zone 88. (See LAXNPWLOX). Wind Advisory in effect from 3 PM this afternoon to 3 AM PDT Wednesday for zones 349-351-352. (See LAXNPWLOX). Red Flag Warning in effect until 6 PM PDT this evening for zones 376>379. (See LAXRFWLOX). PZ...Small Craft Advisory in effect until 3 AM PDT Thursday for zones 645-670-673-676. (See LAXMWWLOX). && $$ PUBLIC...Hall/Schoenfeld/Rorke AVIATION...Rorke MARINE...Sirard/Rorke SYNOPSIS...Hall weather.gov/losangeles Experimental Graphical Hazardous Weather Outlook at: https://www.weather.gov/erh/ghwo?wfo=lox