Area Forecast Discussion
Issued by NWS Los Angeles, CA
Issued by NWS Los Angeles, CA
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123 FXUS66 KLOX 261813 AFDLOX Area Forecast Discussion National Weather Service Los Angeles/Oxnard CA 1113 AM PDT Wed Jun 26 2024 Updated Aviation and Marine Sections .SYNOPSIS...26/922 AM. Expect cooling temperatures through Friday as high pressure weakens over the area and onshore flow strengthens. Night through morning low clouds and fog will become more widespread through the end of the week. Warmer weather is expected over the weekend and into early next week as high pressure returns. && .SHORT TERM (TDY-FRI)...26/928 AM. ***UPDATE*** The marine layer clouds never really made an appearance in LA County this morning, and an eddy is keeping the Santa Barbara area covered. Temperatures are 3-5 degrees cooler this morning than yesterday as the cooling trend kicks off. The exception is in the LA County mountains which had more cloud cover yesterday. No other impactful changes from the previous forecast. ***From Previous Discussion*** Low clouds have become widespread in coastal areas N of Pt. Conception, and were beginning to push into the Santa Ynez Valley. S of Pt. Conception, the stratus field was less organized, but some clouds have pushed into coastal areas from southeastern SBA County to western L.A. County. Clouds should become more widespread in these coastal areas by daybreak, and could even push into the lower valleys of VTU County and the San Gabriel Valley for a few hours. Pressure gradients between KLAX and KDAG were moderately onshore, slightly more so that at this time yesterday morning. Expect skies to clear by mid morning in the valleys and late morning across most of the coastal plain. Clouds could linger at some beaches into the afternoon hours, but even there, skies should eventually become mostly sunny today. The forecast area was sandwiched between the western periphery of a large and strong upper high over New Mexico, and an upper low well of the coast of the Pacific Northwest, with a broad west southwesterly flow pattern aloft overhead. Heights today will change little from those on Tue, but onshore gradients between KLAX and KDAG will be slightly stronger this afternoon. In addition, temps at 950 mb will drop a degree or two. With the addition of some extra marine influence to start the day, expect a couple of degrees of cooling in most areas west of the mtns today, with the best cooling across the coastal plain. Max temps should change little in the mtns and the Antelope Valley. N-S gradients will increase across SBA County and thru the I-5 Corridor later today and tonight, so expect some gusty NW to N winds across the western portions of the south coast of SBA County, the western Santa Ynez mtns and thru the I-5 Corridor. Winds are expected to remain below advisory levels in most areas. The upper low in the Pacific will move into the Pac NW late tonight/Thu, with a trough extending southward into the forecast area. Expect the marine layer to deepen a bit tonight, and clouds should be widespread in coastal areas (with the possible exception of the south coast of SBA County due to the northerly flow. Clouds will have a better chance at pushing more forcefully into the valleys tonight. There could even be some local drizzle, mainly south of Pt Conception. Expect somewhat slower clearing of the low clouds Thu, with a better chance that clouds will linger at some beaches. With lowering heights and cooling at 850 mb and 950 mb, expect a few degrees of cooling just about everywhere Thu. The exception may be on the south coast of SBA County, where temps may edge upward due to downslope northerly flow. A broad trough will linger across the region Thu night and Fri. N-S gradients will peak across SBA County and in the VTU/northwestern L.A. County mtns Thu evening, and winds could reach advisory levels in some areas. Elsewhere, expect little change from tonight/Thu morning, except that low clouds may be a bit more widespread in the valleys. Once again, due to northerly flow, clouds may be limited across southern SBA County or arrive very late Thu night. Expect the clearing pattern Fri to be similar to that on Thu. Additional slight height falls and slightly cooling at 850 mb/950 mb may allow for a bit more cooling in most areas Fri. .LONG TERM (SAT-TUE)...26/508 AM. Heights will rise across the region over the weekend as a large upper high in the south central U.S. begins to expand westward. Expect the marine layer to become increasingly shallow, with less in the way of inland and valley low clouds each night. In fact, low clouds may be squeezed out of most valley areas by Sat night/Sun morning. Rising heights/thicknesses, weakening onshore flow, and less low cloud coverage should lead to a few degrees of warming both Saturday and Sunday. On Sun, max temps will probably exceed 100 degrees in the Antelope Valley and the interior valleys of SLO County, with highs near 100 degrees in some of the warmer locations in the valleys of VTU and L.A. Counties. Heights will remain quite high across the region Mon and Tue, although they will lower a bit as the upper high weakens and shifts eastward. In addition, onshore flow will increase each day. Expect a few degrees of cooling Mon and Tue, especially west of the mtns, with a possible increase in the coverage and inland extend of night through morning low clouds and fog. N-S gradients will increase Sun night and Mon night, which could bring some gusty winds to southern SBA County and the I-5 Corridor, along with a reduction in coastal stratus in southern SBA County. && .AVIATION...26/1811Z. At 17Z over LAX, the marine layer was 1000 feet deep. The top of the inversion was 4000 feet and 23 degrees Celsius. While all sites are VFR now, there is a chance of BKN010 reforming today as early as 20Z at KOXR (30%) and KLAX (10%). High confidence in VFR conditions through Thursday at KPRB KWJF KPMD, moderate confidence at KBUR KVNY. All other sites have a chance ceilings tonight into Thursday: KSBP (60%) KSMX (90%) KSBA (50%) KOXR (80%) KCMA (70%) KSMO (50%) KLAX (50%) KLGB (50%). High confidence that ceilings and visibilities will be similar for the next 24 hours as they have been for the previous 24 hours. Winds will be stronger today than yesterday at KSMX KSBP, and KWJF KPMD where the wind directions will likely have a more northerly component. KLAX...Moderate confidence in VFR conditions through at least 04Z, with a 10% chance of a couple of hours of BKN010 20-02Z. Low confidence on ceilings tonight. 50% chance of BKN008-012 starting as early 03Z and as late 10Z. Southeast winds will likely form after 09Z, but high confidence that they will stay under 8 knots. KBUR...There is a 10% chance of IFR ceilings Thursday 10-15Z, otherwise high confidence VFR conditions through at least Thursday. High confidence in seasonal winds. && .MARINE...26/1111 AM. Dense fog will impact the waters off the Central Coast this morning, with reduced visibilities possibly lasting through the afternoon and evening. There is a moderate threat for dense fog again on Thursday for the same area. High confidence in at least Small Craft Advisory (SCA) winds and seas through Friday Night for the Outer Waters (offshore waters of the Central Coast to San Nicolas Island). There is a 60 percent chance of reaching Gales tonight, especially the northern most areas. For Thursday, the chance for Gales increases to 90 percent for that area. High confidence in Gales ending by Friday morning. Moderate confidence in much less wind on Saturday, but winds will pick up again on Sunday. Elsewhere there the SCA level northwest winds will push into the Santa Barbara Channel but high confidence that they will stay confined to the western half. There is a chance that enough of the channel will be covered with these winds to warrant an SCA...20 percent chance tonight and 40 percent chance on Thursday Night. && .LOX WATCHES/WARNINGS/ADVISORIES... CA...NONE. PZ...Small Craft Advisory in effect until 3 AM PDT Friday for zones 645-676. (See LAXMWWLOX). Small Craft Advisory in effect until 5 PM PDT this afternoon for zone 670. (See LAXMWWLOX). Gale Warning in effect from 5 PM this afternoon to 8 AM PDT Thursday for zone 670. (See LAXMWWLOX). Gale Watch in effect from Thursday morning through late Thursday night for zone 670. (See LAXMWWLOX). Small Craft Advisory in effect until 3 PM PDT Thursday for zone 673. (See LAXMWWLOX). Gale Watch in effect from Thursday afternoon through late Thursday night for zone 673. (See LAXMWWLOX). && $$ PUBLIC...DB AVIATION...Kittell/Lewis MARINE...RK SYNOPSIS...jld weather.gov/losangeles Experimental Graphical Hazardous Weather Outlook at: https://www.weather.gov/erh/ghwo?wfo=lox