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000 FXUS66 KLOX 181113 AFDLOX SOUTHWEST CALIFORNIA AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE LOS ANGELES/OXNARD CA 415 AM PDT THU SEP 18 2008 ...UPDATED AVIATION SECTION... .SHORT TERM... OFFSHORE TRENDS AND MUCH ABOVE NORMAL 850 MB HUMIDITIES HAVE DONE A NUMBER ON THE MARINE LAYER WITH ONLY PATCHY LOW CLOUDS AROUND THE L.A. AND CATALINA COASTS. SMALL WORRY WITH THOSE HIGH 850 DEW POINTS INTERACTING WITH A SMALL DEFORMATION ZONE AND BUBBLING UP SOME CONVECTION EARLY THIS MORNING...BUT SATELLITE SHOWS NO ACTIVITY AND KEPT MENTION OUT OF THE FORECAST BUT WILL HAVE TO MONITOR. THIS AFTERNOON THAT SAME MOISTURE WILL CAUSE PARTLY CLOUDY SKIES AND A SLIGHT CHANCE OF TSTMS OVER THE VTA AND LA MTNS AS WELL AS THE ANTELOPE VALLEY. MDLS CONTINUE TO SHOW NO MARINE LAYER TONIGHT AS THEY HAVE BEEN FOR THE PAST FEW DAYS AND GIVEN THE CLEAR SKIES AT THE MOMENT WILL KEEP SKIES CLEAR. TEMPS WILL BE VERY SIMILAR TO TODAYS VALUES BUT SINCE THERE WILL BE NO MID LEVEL MOISTURE THERE WILL BE NO TSTM THREAT. IN THE WAKE OF A WEAK TROF ONSHORE FLOW SHOULD INCREASE ENOUGH TO BRING MARINE CLOUDS BACK TO THE CENTRAL COAST. THERE IS A CHANCE OF LOW CLOUDS SOUTH OF POINT CONCEPTION BUT FOR NOW WILL LEAVE THEM OUT. LOOK FOR A WEAK SUNDOWNER BOTH TONIGHT AND FRIDAY NIGHT WITH A LITTLE NW UPPER PUSH AND A MINUS 3 SMX-SBA GRADIENT. .LONG TERM... MEDIUM RANGE MDLS HAVE FINALLY COME INTO SOME SORT OF AGREEMENT FOR THE EXTENDED FORECAST. THE WEEKEND LOOKS FAIRLY BLAND WITH A FLAT TROF SITTING OVER THE WEST COAST. THIS SHOULD BRING THE MARINE LAYER BACK TO THE COASTAL SECTIONS AND MAYBE SOME PATCHES INTO THE COASTAL VLYS. A LITTLE LOWER HGTS AND STRONGER ONSHORE FLOW WILL DROP TEMPS A FEW MORE DEGREES. THE TROF SHARPENS AND DIVES SOUTH MONDAY AND EXITS EARLY TUESDAY AND THIS SHOULD LIFT THE MARINE LAYER INTO THE VLYS. A HIGH WILL BUILD INTO NEVADA IN THE WAKE OF THIS TROF AND BY WEDNESDAY THE FIRST OFFSHORE EVENT OF THE SEASON COULD SHAPE UP. BUT THE GFS IS A LITTLE OFFSHORE HAPPY AND THIS FORECAST COULD CHANGE BY THEN. && .AVIATION... 18/1100Z. LATEST ACARS SHOWS LITTLE IF ANY MARINE LAYER...BUT SATELLITE SHOWS SOME PATCHY CLOUDS IN THE SANTA MONICA BASIN AND THESE CLOUDS WILL AFFECT KLGB TO KNTD AT TIMES THROUGH MID MORNING. THERE IS A 10 PERCENT CHC OF A TSTM THIS MORNING OVER L.A. COUNTY. THERE WILL BE BUILD UPS OVER THE L.A. MTNS THIS AFTERNOON WITH A 20 PERCENT CHANCE OF TSTMS MID AFTERNOON THROUGH EARLY EVENING. MARINE LAYER CLOUDS RETURN TONIGHT IS QUESTIONABLE...MORE LIKELY ON THE CENTRAL COAST AND TO THE L.A. COAST AFTER 12Z. KLAX...GOOD CONFIDENCE IN 16Z BURN OFF PLUS OR MINUS ONE HOUR. 30 PERCENT CHANCE OF MVFR CLOUDS FORM 08Z TO 12Z TONIGHT. KBUR...HIGH CONFIDENCE IN CAVU TAF. A 20 PERCENT CHANCE OF 5SM IN HZ IN THE EARLY MORNING. && .LOX WATCHES/WARNINGS/ADVISORIES... SMALL CRAFT ADVISORY (SEE LAXMWWLOX). && $$ PUBLIC...RORKE AVIATION...BRUNO WWW.WEATHER.GOV/LOSANGELES