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000 FXUS66 KLOX 181830 AFDLOX SOUTHWEST CALIFORNIA AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE LOS ANGELES/OXNARD CA 1130 AM PDT THU SEP 18 2008 NEW AVIATION DISCUSSION .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...18/1830Z. MOSTLY CLEAR SKIES WILL CONTINUE THROUGH THIS EVENING BEFORE LOW CLOUDS AND FOG RETURN TO ALL THE COASTAL TAFS SOMETIME AROUND MIDNIGHT...GIVE OR TAKE A COUPLE OF HOURS. MVFR TO IFR CONDITIONS ARE THEN EXPECTED THROUGH MID MORNING ON FRIDAY. VALLEY TAFS WILL LIKELY REMAIN CLEAR THROUGH FRIDAY. KLAX...CLEAR SKIES THROUGH ABOUT MIDNIGHT...THEN A 70 PERCENT CHANCE OF LOW CLOUDS AND FOG WITH MVFR TO IFR CONDITIONS FROM MIDNIGHT THROUGH MID MORNING FRIDAY. KBUR...A 70 PERCENT CHANCE OF CLEAR SKIES THROUGH FRIDAY. && .LOX WATCHES/WARNINGS/ADVISORIES... SMALL CRAFT ADVISORY (SEE LAXMWWLOX). && $$ PUBLIC...RORKE AVIATION...SWEET WWW.WEATHER.GOV/LOSANGELES