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000 FXUS66 KLOX 171657 AFDLOX SOUTHWEST CALIFORNIA AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE LOS ANGELES/OXNARD CA 955 AM PDT WED SEP 17 2008 .SHORT TERM (TODAY-FRI)...MARINE LAYER RANGED THIS MORNING FROM 1400 FT DEEP AT LAX TO NEAR 2200 FT AT VBG. LOW CLOUDS OVER MANY VALLEY AND COASTAL AREAS WERE CLEARING RATHER QUICKLY BACK TO THE COAST THROUGH MID MORNING. SOME LOW CLOUDS MAY LINGER AT THE BEACHES S OF POINT CONCEPTION THIS AFTERNOON...OTHERWISE MOST OF THE LOW CLOUDS SHOULD CLEAR OFF THE COAST. MOISTURE COMING IN FROM THE S AT LOWER TO MID LEVELS WILL BRING PARTLY CLOUDY SKIES TO PORTIONS OF VTU/L.A. COUNTIES THIS AFTERNOON. THERE IS ALSO A SLIGHT CHANCE OF THUNDERSTORMS THIS AFTERNOON AND EARLY EVENING IN THE MOUNTAINS OF VTU/L.A. COUNTIES AND THE ANTELOPE VALLEY...ALTHO AN INVERSION AT AROUND 15000 FT AS SHOWN ON MORNING SOUNDINGS MAY INHIBIT CONVECTION TO SOME DEGREE. TEMPS TODAY ACROSS THE REGION WILL BE GENERALLY NEAR NORMAL FOR MOST AREAS. A BROAD SOUTHWESTERLY FLOW ALOFT WILL PREVAIL OVER THE FORECAST AREA THROUGH FRI AS AN UPPER LEVEL TROF APPROACHES THE COAST. AT LOWER TO MID LEVELS...THE FLOW WILL BE MORE SOUTHERLY WHICH WILL HELP TO BRING IN SIGNIFICANT LOWER TO MID LEVEL MOISTURE FROM OFF THE BAJA COAST MAINLY TO VTU/L.A. COUNTIES TONIGHT INTO EARLY THU. THE WRF IS FORECASTING 850 MB DEWPOINTS TO INCREASE TO 12 TO 16 DEG C OVER THE REGION...WITH PWAT VALUES INCREASING TO AS HIGH AS 1.6 INCHES ALONG THE COAST. THE INCREASING MOISTURE AT 850 MB SHOULD HELP TO DESTABILIZE THE LOWER ATMOSPHERE ABOVE THE MARINE LAYER TO THE MID LEVELS...AS SHOWN IN WRF SHOWALTER INDEX CHARTS (AS LOW AT -3 ALONG THE VTU/L.A. COASTAL AREAS TONIGHT). THE WRF IS FORECASTING K-INDEX VALUES INCREASING TO 35 TO NEAR 40 TONIGHT FOR MUCH OF THE AREA. IN ADDITION...THE GFS IS SUPPORTING THE IDEA OF INCREASING LOWER LEVEL MOISTURE OVER THE REGION DURING THE PERIOD. IT LOOKS MORE AND MORE LIKE THERE WILL BE THE POSSIBILITY OF A FEW SHOWERS AND EVEN AN ISOLATED THUNDERSTORM OVER VTU/L.A. COUNTIES TONIGHT. THIS WILL LIKELY BE REFLECTED IN THE AFTERNOON ZONE PACKAGE. FOR NOW HAVE OPTED TO INTRODUCE PARTLY CLOUDY SKIES TO THE REGION FOR THIS AFTERNOON AND TONIGHT. ALTHO SOME MID LEVEL MOISTURE SHOULD LINGER THU...IT LOOKS LIKE THE THREAT OF AFTERNOON THUNDERSTORMS FOR THE MTNS OF VTU/L.A. COUNTIES WILL BE MINIMAL AT BEST WITH JUST SOME CU BUILDUPS POSSIBLE. MARINE LAYER CLOUDS MAY BE HARD PRESSED TO BECOME ORGANIZED TONIGHT S OF POINT CONCEPTION...OTHERWISE PLENTY OF LOW CLOUDS AND FOG NIGHT AND MORNING HOURS CAN BE EXPECTED THRU FRI FOR THE COAST AND VALLEYS. HI TEMPS ARE FORECAST TO BE NEAR NORMAL FOR THE MOST PART ON THU THEN COOL TO SLIGHTLY BELOW NORMAL FOR FRI. ...FROM PREVIOUS DISCUSSION... .LONG TERM (FRI NIGHT-WED)...THE IMPULSE ON FRIDAY CONTINUES TO FLUMMOX THE MEDIUM RANGE MODELS. SATURDAYS FORECAST LOOKS ON TRACK WITH THE LOW MOVING OUT AND HGTS RISING THE MARINE LAYER SHOULD SHRINK A LITTLE AND TEMPS SHOULD WARM A FEW DEGREES. AFTER SATURDAY THE MDLS GO THEIR OWN WAYS AND THE GFS ENSEMBLES BOMB-BURST INTO A SQUIGGLY MESS. WITH LITTLE OR NO CONFIDENCE IN THE LONG RANGE FORECAST MADE A FEW ADJUSTMENT TOWARD CLIMATOLOGY BUT IN GENERAL LEFT THINGS UNCHANGED FROM SUNDAY ON. HOPEFULLY THE MODELS WILL GET A HANDLE ON FRIDAYS IMPULSE AND THE MEDIUM RANGE MDLS WILL GET A HANDLE ON THINGS. && .AVIATION... 17/1100Z MARINE LAYER IS NEAR 1300 FEET AND PUSHED IN NICELY BY A 3 MB GRADIENT. CIGS ARE HIGH ENOUGH TO MAKE IT INTO THE VLYS BUT WILL ALSO BE HIGH ENOUGH TO NOT PRESENT MUCH OF VISIBILITY PROBLEM. THE CENTRAL COAST WILL BE SLOW TO CLEAR. THE MARINE CLOUD PATTERN THIS EVENING AND OVERNIGHT SHOULD BE VERY SIMILAR TO YDY NIGHT. KLAX...VERY GOOD CONFIDENCE IN 12Z TAF. CIG CLEARING WILL VERY LIKELY BE WITHIN AN HOUR OF FORECAST. KBUR...GOOD CONFIDENCE IN TH 12Z TAF. CIG BURN OFF COULD BE ONE OR TWO HOURS LATER THAN FORECAST. CIG ARRIVAL TONIGHT WILL BE AFTER MIDNIGHT AND MORE LIKELY TOWARD DAWN. && .LOX WATCHES/WARNINGS/ADVISORIES... SMALL CRAFT ADVISORY (SEE LAXMWWLOX). && $$ PUBLIC...SIRARD/RORKE AVIATION...BRUNO WWW.WEATHER.GOV/LOSANGELES