Area Forecast Discussion
Issued by NWS Los Angeles, CA

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901 FXUS66 KLOX 271619 AFDLOX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE LOS ANGELES/OXNARD CA 919 AM PDT FRI MAY 27 2016 .SYNOPSIS... Weak low pressure will linger over the area keeping temperatures a little below normal through Sunday. There is a slight chance of mountain showers or thunderstorms Saturday afternoon and early evening. Next week, high pressure will build in causing a gradual warming trend in inland areas while the coastal temperatures will remain steady. && .SHORT TERM...(TDY-SUN) There was a more well-defined marine inversion this morning at around 1700 ft deep at KVBG and around 2000 ft deep at KLAX. At mid morning, low clouds covered the Central Coast, Santa Ynez Vly, and L.A. County coastal area, with patchy low clouds into the San Gabriel Vly. The eddy over the SoCal bight was pushing low clouds into the VTU County coast as well. The low clouds are forecast to dissipate as the morning progresses, altho may linger into early afternoon at some of the beaches. Otherwise, mostly sunny skies should prevail thru the afternoon, except pop-up cu is likely over the mtns for partly cloudy skies there. Good onshore flow can be expected this afternoon into early evening, with gusty sw to nw winds from the Central Coast to the foothills, mtns and deserts. Temps this afternoon will remain several degrees cooler-than-normal for the coast/vlys, but warm to near to slightly above normal for interior areas and deserts. A broad mainly nw flow aloft will prevail over swrn CA thru today as upper level ridging lingers off the coast. A weak, baggy upper level trof will develop over srn CA tonight and linger over the area Sat while developing into a weak upper level low. The weak upper low will then drift se across the forecast area Sat night and into sern CA for Sun. The marine inversion will remain in place over the next few of days. This will help more extensive night and morning low clouds and fog to affect the coast and adjacent vlys tonight thru Sun morning, with an eddy enhancing the marine layer clouds s of Pt Conception. There will be the possibility of afternoon cu buildups in the mtns Sat and Sun, altho the 12Z NAM was indicating there should be enough moisture and instability for the formation of isolated showers or thunderstorms Sat afternoon in the VTU/interior SBA County mtns. LI`s down to -5, CAPE values over 1100 J/kg, and the presence of the weak upper troffiness would support this possibility as well. Have decided to put back into the fcst a slight chance of thunderstorms for these areas, and also into the L.A. County mtns along the I-5 corridor, for Sat afternoon into the evening. In addition, there is slim, non-zero chance of a shower or thunderstorm over the San Gabriel Mtns Sun afternoon as the upper low slides off to the se, but POPS in this area will be below 15 percent so there is no mention in the zones. Otherwise, mostly clear skies are expected over the forecast area tonight thru Sun. Weaker onshore flow is expected each afternoon and evening, with locally gusty sw to nw winds from the Central Coast to the foothills, mtns and deserts. Temps are forecast to change little for Sat thru Sun. Highs will be generally 3 to 6 deg below normal for the cst and adjacent vlys, while inland vlys, mtns and deserts will be near normal to slightly above seasonal norms. ***FROM PREVIOUS DISCUSSION*** .LONG TERM...(MON-THU) Both the ECMWF and GFS are in pretty good agreement during the extended period. The upper low will will shift east as an upper ridge will build in from the eastern Pacific and persist through at least next Wed before weakening as a broad upper level trof over the e Pac approaches. The models start to diverge on Wednesday as the ECMWF holds onto the upper ridging more so than the GFS by Thu. Overall, it looks like a typical June gloom marine layer pattern will prevail during the extended period with night and morning low clouds and fog for the coast and coastal vlys. The marine layer could be disturbed a bit across the central coast Monday night/Tue Morning, and again the following night and morning due to some weak offshore winds, but expect some patchy low clouds to develop. Sundowner winds should also keep the SBA south coast mostly clear with little chance of low clouds during the same time period mentioned. Temps are forecast to become increasingly warm and several degrees above normal over interior areas, while the coast and adjacent vlys will be near normal to a few degrees below normal thru the week. The warmest day next week is expected to be on Wed with highs from the upper 60s and 70s at the coast to upper 70s and 80s for the vlys and foothills, except warming into the lower to mid 90s in the Antelope vly. && .AVIATION...27/1145Z. At 11Z at KLAX...The marine layer was 2000 feet deep. The top of inversion was 4500 ft with a temperature of 15 degrees Celsius. N of Pt Conception, low clouds were widespread on the Central Coast and in the Santa Ynez Valley, and were spilling into the Salinas Valley. S of Pt Conception, clouds were beginning to push into south coastal sections of L.A. County, and will become widespread across coastal sections by daybreak. Clouds will likely push into the San Gabriel Valley. Conditions were mostly low MVFR S of Pt Conception, and IFR north. Expect skies to clear in most areas by mid to late morning, except maybe early afternoon near the beaches. More widespread low clouds are expected tonight/Sat morning, with clouds expected in all coastal and most valley areas. Conds should be mainly low MVFR or high IFR tonight. KLAX...Moderate confidence in the 12z TAF. There is a 30 percent chance that cigs will scatter out as early as 17z. There is a 30 percent chance that cigs tonight will not arrive until 06z or later. KBUR...Moderate confidence in the 12z TAF. There is a 30 percent chance of MVFR cigs between 13z and 17z this morning. There is a 20 to 30 percent chance that cigs will arrive as early as 07z tonight, and could be at IFR levels. && .MARINE...27/900 AM. Northwest winds from Piedras Blancas to San Nicolas Island will prevail through late tonight and small craft advisory conditions will prevail. Otherwise a Catalina eddy is expected to develop each night over the bight through Tuesday and northwest winds are expected elsewhere and fill in the bight each afternoon. A complex storm system over the Southern Ocean last Monday with a fetch oriented 190-210 degrees from Ventura generated swells that will arrive Monday and build through Tuesday. The swells will remain below small craft advisory for hazardous sea conditions but there will be extra surging and currents along exposed south facing shores. In the meantime a small south swell will continue and a locally generated swell from 310-330 degrees will subside Saturday night. && .LOX WATCHES/WARNINGS/ADVISORIES... CA...NONE. PZ...Small Craft Advisory in effect until 3 AM PDT Saturday For zones 670-673-676. (See LAXMWWLOX). && $$ PUBLIC...Sirard/CK AVIATION...DB MARINE...30 SYNOPSIS...JLD weather.gov/losangeles

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