Area Forecast Discussion
Issued by NWS Los Angeles, CA

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000 FXUS66 KLOX 290305 AFDLOX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE LOS ANGELES/OXNARD CA 805 PM PDT THU APR 28 2016 .SYNOPSIS... Mostly clear except a coastal low may bring an overnight marine layer into early Saturday with patchy drizzle. A low will approach from the East on Saturday with a slight chance of showers and thunderstorms...with showers to linger in the deserts on Sunday. A high will arrive by Monday with a warming trend...but by midweek a low should approach with possible precipitation on Thursday. && .SHORT TERM...(TONIGHT-SUN) Upper level low pressure system currently centered over northern Arizona will shift northeastward into Colorado by tomorrow afternoon. Behind this system, there is still fairly strong northwest flow aloft across Southwest California that will continue to generate cool and breezy conditions for many areas through Friday. For tonight, the strongest winds will be focused across the Santa Ynez mountains and Santa Barbara south coast, as well as the I-5 corridor of the LA County mountains, where gusts between 40 and 50 mph can be expected. The gale force northwest winds near Point Concpetion will help to generate a Catalina eddy circulation across the inner waters tonight into Friday morning. Already seeing pronounced south winds at Long Beach this evening which seems to confirm that an eddy circulation will be underway soon. Local WRF model shows a fairly strong eddy circulation spinning up tonight with southeast-east winds of 10 to 15 knots developing in the San Pedro Channel and Santa Monica Bay. This eddy circulation should help to spin up considerable low clouds across the LA coast/valleys tonight, potentially reaching the Ventura coast on Friday morning. The marine layer is expected to deepen to around 2000 feet by Friday morning across the LA Basin. Should also see fairly extensive low clouds forming tonight north of Point Conception along the Central Coast and Santa Ynez Valley. Low clouds are expected to burn off inland on Friday afternoon, but could see some low clouds linger near some of the coastal areas. *** From previous discussion *** Another eddy will form Fri night with low clouds again expected for the cst and some vlys of L.A./VTU County Fri night into Sat morning. The marine layer should turn a bit deeper thanks to the approaching upper level low, and patchy drizzle will not be out of the question by Sat morning. Low clouds and fog should also develop over the central Coast and santa Ynez Vly and Salinas Vly Fri night into Sat morning. Otherwise, mostly clear skies can be expected across the region Fri night into Sat, except for some mid level cloudiness by Sat afternoon from the nearby upper low. There will also be enough moisture and instability Sat afternoon for a slight chance of thunderstorms for the L.A. County mtns and Antelope Vly, with the potential of a thunderstorm drifting into the Santa Clarita Valley and San Gabriel Vly, especially near the foothills. Gusty w to n winds are expected again late Fri and Fri night for the mtns, Antelope vly, and SBA County s cst, where advisory level wind gusts will be possible in some areas. Gusty sub-advisory level nw winds can also be expected along the Central Coast Fri afternoon and early evening. It looks like another eddy will form over the SoCal bight Sat night into Sun morning, with marine layer clouds and fog expected to spread into the L.A./VTU County coast and some vlys Sat night and to the SBA County S coast early Sun Morning. Offshore flow will develop over SLO/SBA Counties Sat night into Sun morning to keep low clouds away from the Central Coast. Otherwise, clear to partly cloudy skies can be expected over the forecast area for the second half of the weekend. Some moisture, cyclonic flow aloft, and increased instability with strong May sunshine on Sun will result in a slight chance of thunderstorms Sun afternoon and early evening over the mtns of L.A./VTU/SBA Counties and across the Antelope Vly. Temps over the area will continue to be a few degrees below normal for many areas Fri thru Sun, altho should warm some to closer to normal to slightly above normal for portions of SLO County, and in the mtns and Antelope Vly, especially Fri and Sun. .LONG TERM...(MON-THU) The EC/GFS are in good agreement overall in the large scale features Mon thru Thu. The upper trof will move e for Mon with a weak upper ridge moving into srn CA for Mon and Mon night. A large upper level trof is forecast to develop over the e Pac by Tue and slowly edge its way toward SoCal thru Thu. Dry weather can be expected over the region Mon thru Wed. Marine layer clouds should affect the coast and some vlys Sun night into Mon morning, otherwise mostly clear skies can be expected Mon thru Wed across the region. A low pressure system associated with the deep upper trof will approach the forecast area Wed night and thu, spreading some moisture into the region by Thu. There should be increasing clouds Wed night followed by a slight chance of showers developing on Thu. Since we are seven days away from this event, there is only moderate confidence at best that pcpn will develop on Thu. Further model runs should boost our confidence in this late season weather event if models continue to be consistent. There is even the potential for more significant pcpn in showers and possible thunderstorms beyond the fcst period late next week as the upper trof moves inland. && .AVIATION...28/2335Z... At 2300Z, Marine layer at LAX is 1400 feet with inversion top temperature of 11.8 degrees celsius at 3700 feet. Residual moisture and instability may generate isolated rain showers through the early evening hours. Otherwise onshore flow and low level moisture near the surface will likely bring mvfr cigs into many coastal/valley areas tonight into Friday morning. Eddy circulation expected to develop overnight which should deepen the marine layer to around 2000 feet by Friday morning across the LA Basin, resulting in low clouds reaching the valleys. Gusty onshore winds each afternoon and evening, with mdt uddfs and llws vcnty ksba during evening hours. KLAX...Mvfr cigs likely overnight but timing could differ +/- 2 hours from TAF timing. Eddy circulation likely to bring east-southeast surface winds late tonight into Friday morning, but only a 20 percent chance that it could reach 10 kt. A 20 percent chance of mvfr cigs lingering into the afternoon hours on Friday. KBUR...Mvfr cigs likely by around sunrise on Friday morning, with a 20 percent chance of brief ifr conditions. && .MARINE...28/800 pM... Northwest winds are beginning to subside over the outer waters...but gale force gusts are likely to continue between San Nicolas Island and Santa Rosa Island until the early morning hours. Small Craft Advisory winds and seas are expected near-shore in the Santa Barbara Channel and north of Point Sal. Northwest winds will increase again Friday night and small craft advisory conditions with gale gusts are likely again from Piedras Blancas to Point Sal 10-60nm and from Point Sal to San Clemente Island through Saturday morning. Seas over 10 feet and small craft advisory for hazardous sea conditions from Piedras Blancas to San Clemente Island through Saturday night as gales north of the area persist. A south swell is expected to arrive Saturday and extra currents and surging as well as hazardous surf are likely along exposed south facing shores. && .LOX WATCHES/WARNINGS/ADVISORIES... CA...Wind Advisory in effect until 9 PM PDT this evening For zones 34-35-59-87. (See LAXNPWLOX). Beach Hazards Statement in effect until 9 PM PDT this evening For zones 34-35-40-41-87. (See LAXCFWLOX). Wind Advisory in effect until 3 AM PDT Friday For zones 39-52>54. (See LAXNPWLOX). PZ...Gale Warning in effect until 9 PM PDT this evening For zones 645-670-673. (See LAXMWWLOX). Small Craft Advisory in effect until 9 PM PDT this evening For zones 650-655. (See LAXMWWLOX). Gale Warning in effect until 3 AM PDT Friday For zone 676. (See LAXMWWLOX). && $$ PUBLIC...Gomberg/Sirard AVIATION...Gomberg MARINE...Smith SYNOPSIS...Seto is the U.S. government's official web portal to all federal, state and local government web resources and services.