000 FXUS66 KLOX 292030 AFDLOX SOUTHWEST CALIFORNIA AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE LOS ANGELES/OXNARD CA 130 PM PDT FRI MAY 29 2009 NEW AVIATION DISCUSSION .SHORT TERM...OVERALL...TODAY IS SHAPING UP TO BE VERY SIMILAR TO THURSDAY. MID-LEVEL FLOW ON SOUNDINGS AND MODELS CONTINUES TO BE SOUTHEASTERLY THIS MORNING AND AFTERNOON. SO...MID-LEVEL MOISTURE WILL LIKELY CONTINUE ACROSS THE AREA THROUGH THE EVENING...RESULTING IN ANOTHER ROUND OF AFTERNOON CONVECTION. AT THIS TIME...THE NORTHERN SECTIONS OF VTU/SBA COUNTIES AND SOUTHERN SLO COUNTY LOOK VULNERABLE TODAY. IN ADDITION...IT APPEARS THE MOISTURE AND INSTABILITY WILL BE BETTER OVER LAX COUNTY THIS AFTERNOON...SO WILL EXPECT BIT MORE CONVECTIVE DEVELOPMENT OVER THE MOUNTAINS AND POTENTIALLY THE ANTELOPE VALLEY. RADAR WILL BE WATCHED VERY CLOSELY TODAY AS THE POTENTIAL FOR WARNING-LEVEL STORMS IS PRESENT. OTHERWISE...EXPECT A TYPICAL MARINE LAYER DAY FOR THE COASTS AND COASTAL VALLEYS. CURRENT AMDAR SOUNDINGS INDICATE MARINE INVERSION AROUND 2500 FEET WITH STRATUS IN THE SANTA CLARITA VALLEY. EXPECT A VERY SIMILAR BURNOFF AS THURSDAY...WITH SOME CLOUDS LIKELY TO LINGER ALONG THE COAST THROUGH THE AFTERNOON. OVERALL...CURRENT ZONES LOOK GOOD AND NO UPDATES ARE PLANNED. NOW JUST WAIT AND SEE WHAT HAPPENS THIS AFTERNOON WITH THE CONVECTION. *** LONG TERM FROM PREVIOUS DISCUSSION *** .LONG TERM (MONDAY-THURSDAY)...MODELS ARE STARTING TO DIVERGE ON THE DEVELOPMENT OF A TROUGH OVER THE EASTERN PACIFIC. AS INDICATED IN EARLIER DISCUSSIONS...THE MOVEMENT REMAINS UNPREDICTABLE FROM RUN-TO-RUN DUE TO THE TROUGH BEING CUTOFF FROM THE FLOW PATTERN. THE LATEST ECMWF SOLUTION HAS SWITCHED POSITIONS WITH THE GFS FROM THIS TIME LAST NIGHT...BECOMING LESS PROGRESSIVE IN NATURE WITH THE STORM SYSTEM. FOR THE CURRENT TIME...AN ONSHORE FLOW REGIME WILL PERSIST THROUGH THE LONG TERM PERIOD. THE TROUGH WILL LIKELY BRING FURTHER COOLING AND THE PACKAGE TRENDS THAT WAY WITH PARTLY CLOUDY SKIES. LOW CONFIDENCE SHOULD STILL BE PLACED IN THE TIMING AND EXACT MOVEMENT OF THE SYSTEM AT THIS TIME. THE PACKAGE HAS INTRODUCED POPS AND MENTION OF WEATHER FOR AREAS NORTH OF POINT CONCEPTION DUE THE AGREEMENT IN TIME OF THE SOME INGREDIENTS AMONG THE GFS AND ECMWF SOLUTIONS. HOWEVER...A SLOWING OF THE SYSTEM WOULD NOT BE SURPRISING. && .AVIATION...29/2030Z. A TALE OF TWO ATMOSPHERES...THE BOUNDARY LAYER IS MIRED IN STRATUS AS A RESULT OF THE MARINE LAYER...AND ABOVE THE MARINE LAYER THE MID LEVELS OF THE ATMOSPHERE ARE QUITE UNSTABLE WITH THUNDERSTORMS DEVELOPING OVER THE ANTELOPE VALLEY. IN ALL...IT IS A COMPLEX FORECAST WITH DECREASING CONFIDENCE IN THE EVOLUTION. ANY THUNDERSTORMS HAVE THE POTENTIAL TO RELEASE AN OUTFLOW BOUNDARY WHICH COULD EASILY DISPERSE THE MARINE LAYER AT A MOMENTS NOTICE. SINCE THE VALLEY TAFS ARE CLOSEST TO THUNDERSTORM ACTIVITY...KBUR AND KVNY COULD BECOME FREE OF THE LOW STRATUS IN THE NEXT COUPLE OF HOURS DUE TO NEARBY CONVECTION. THE COASTAL TAFS...ON THE OTHER HAND...HAVE THE POTENTIAL TO STAY MIRED IN LOW CLOUDS AND FOG ALL DAY UNLESS THERE IS WIDESPREAD THUNDERSTORM ACTIVITY THAT SPREADS INTO THE COASTAL SECTIONS. FOR NOW...WILL EXPECT THE COASTAL SECTIONS TO REMAIN UNAFFECTED BY THUNDERSTORM ACTIVITY. KLAX...MVFR CONDITIONS WITH CEILINGS LASTING THROUGH THE DAY. THERE IS A 20 PERCENT CHANCE OF CLEARING THIS AFTERNOON. THEN...LOW CLOUDS SHOULD BECOME REESTABLISHED OVER THE AIRFIELD EARLY THIS EVENING AND CONTINUE INTO SATURDAY MORNING. KBUR...MVFR CONDITIONS WITH CEILINGS LASTING THROUGH THE DAY. THERE IS A 50 PERCENT CHANCE OF CLEARING THIS AFTERNOON...AND A 20 PERCENT CHANCE OF A GLANCING BLOW FROM A NEARBY THUNDERSTORM THIS AFTERNOON. THEN...LOW CLOUDS SHOULD BECOME REESTABLISHED OVER THE AIRFIELD LATER THIS EVENING AND CONTINUE INTO SATURDAY MORNING WITH MVFR TO LOCAL IFR CONDITIONS. && .LOX WATCHES/WARNINGS/ADVISORIES... NONE && $$ PUBLIC...THOMPSON AVIATION...SWEET WWW.WEATHER.GOV/LOSANGELES