FXUS66 KLOX 172054 
  AFDLOX 
   
  SOUTHWEST CALIFORNIA AREA FORECAST DISCUSSION 
  NATIONAL WEATHER SERVICE LOS ANGELES/OXNARD CA 
  155 PM PDT WED MAR 17 2010 
   
  .SYNOPSIS... 
   
  MOSTLY SUNNY AND WARM TODAY WITH A COOLING TREND INTO FRIDAY AS LOW 
  PRESSURE WILL BRING NIGHT AND MORNING LOW CLOUDS AND FOG ALONG THE 
  COAST. HIGH PRESSURE WILL BRING ANOTHER WARMING TREND FOR THE WEEKEND 
  WITH WEAK OFFSHORE FLOW.      
   
  && 
   
  .SHORT TERM (TODAY-SAT)...GRADIENTS FINALLY TRENDING ONSHORE THIS  
  AFTERNOON BUT NOT BEFORE TEMPS SHOT UP TO PRETTY MUCH THE SAME AS  
  TUESDAY`S LEVELS, IF NOT WARMER IN A FEW PLACES. CONSIDERABLE  
  COOLING EXPECTED THU AS A SHALLOW MARINE INVERSION DEVELOPS TONIGHT  
  AND WEAK ONSHORE FLOW PUSHES THIS COOLER AIR INLAND. VISIBLE SAT  
  IMAGERY SHOWING SOME LOW CLOUDS DEVELOPING WELL OFFSHORE THIS  
  AFTERNOON AND WE SHOULD SEE THIS EXPANDING EASTWARD OVERNIGHT. AREAS  
  OF DENSE FOG POSSIBLE ALONG THE COAST OF LA COUNTY LATER TONIGHT AND  
  WOULD NOT BE TOTALLY SURPRISED TO SEE CLOUDS AS FAR NORTH AS VENTURA  
  COUNTY.  
   
  A WEAK SYSTEM MOVING INTO THE PAC NW TONIGHT WILL DROP SOUTH ALONG  
  THE WEST COAST THURSDAY AND THURSDAY NIGHT, PASSING THROUGH SO CAL  
  AS A DRY INSIDE SLIDER FRIDAY MORNING. ALTHOUGH THE TIMING OF THIS  
  TROF PASSAGE IS SIMILAR TO YESTERDAY`S MODELS, THE MODELS HAVE SPED  
  UP THE ARRIVAL OF NORTHEAST WINDS BY 12-18 HOURS, WHICH MAKES FRIDAY  
  A VERY TRICKY FORECAST. THERE WILL BE A BATTLE BETWEEN THE  
  INCREASING LOW LVL MOISTURE UNDER A PRETTY STRONG MARINE INVERSION  
  AND THE DEVELOPING OFFSHORE GRADIENT BEHIND THE TROF. MORE OFTEN  
  THAN NOT THE MARINE LYR WINS THE BATTLE, AT LEAST INITIALLY, AND LOW  
  CLOUDS HANG IN THERE LONGER THAN EXPECTED. FOR THIS REASON, THE  
  SPREAD OF POSSIBLE HIGH TEMPERATURES FRIDAY IS QUITE A BIT LARGER  
  THAN USUAL. FOR NOW DECIDED NOT TO MAKE TOO MANY CHANGES TO THE  
  FRIDAY FORECAST GIVEN THE UNCERTAINTY, BUT MOS GUIDANCE CERTAINLY IS  
  FAVORING A RAPID AND EARLY MARINE LYR CLEARING WITH NORTHEAST WINDS  
  ARRIVING AT THE COAST BEFORE SUNRISE FRIDAY. AS USUAL THE NAM IS  
  STRONGER WITH THE OFFSHORE WINDS AND IS CALLING FOR ADVISORY LEVEL  
  WINDS IN THE VENTURA AND LA COUNTY MOUNTAINS AND VALLEYS LATE  
  THURSDAY NIGHT THROUGH EARLY AFTERNOON FRIDAY. WILL SEE IF THIS  
  REMAINS THE CASE WITH THE NEXT FEW MODEL RUNS. 
   
  A SIMILARLY TRICKY FORECAST SATURDAY. SURFACE GRADIENTS REMAIN ABOUT  
  THE SAME AS FRIDAY, THOUGH UPPER SUPPORT FOR GUSTY WINDS IS  
  SIGNIFICANTLY LESS. THE AIRMASS AS A WHOLE IS WARMER WITH THE RIDGE  
  AXIS ALMOST DIRECTLY OVERHEAD, HOWEVER THE NAM IS STILL SHOWING A  
  SHALLOW, BUT FAIRLY WIDESPREAD LOW LVL MOISTURE FIELD ACROSS THE  
  COASTAL AREAS WITH WEAK SOUTHEAST FLOW SOUTH OF PT CONCEPTION. IF  
  THE MARINE LYR IS NOT COMPLETELY WIPED OUT FROM FRIDAY`S OFFSHORE  
  FLOW THEN CLOUDS COULD EASILY LINGER INTO SATURDAY MORNING,  
  RESULTING IN A DIFFICULT FORECAST FOR HIGHS SATURDAY. MOS GUIDANCE  
  NUMBERS TREND MOST AREAS 3-6 DEGREES WARMER, BUT THIS MAY BE  
  OVERDONE, ESPECIALLY FOR THE COAST. THE CURRENT FORECAST TRENDS ARE  
  A LITTLE MORE CONSERVATIVE GIVEN THIS UNCERTAINTY. 
   
  .LONG TERM (SUN-WED)...WHILE YESTERDAY`S MODELS STRONGLY FAVORED  
  SUNDAY AS BEING THE WARMEST DAY, IT NOW APPEARS THAT MOST AREAS  
  SHOULD START TRENDING COOLER SUNDAY AS THE RIDGE WEAKENS AND A TROF  
  APPROACHES FROM THE WEST. THERE STILL IS WEAK OFFSHORE FLOW AT THE  
  SURFACE, AND HIGHS SHOULD STILL BE WELL ABOVE NORMAL, ESPECIALLY  
  INLAND, BUT FOR NOW I`VE EITHER GONE WITH LITTLE CHANGE OR SLIGHTLY  
  COOLER SUNDAY. THE APPROACHING TROF WILL DEFINITELY BRING IN MUCH  
  COOLER DAYS EARLY NEXT WEEK, BUT STILL NO PRECIP. THE COOLEST DAY  
  WILL BE TUESDAY AS A TROF DIVES SOUTH THROUGH THE GREAT BASIN. THEN  
  WARMER WEDNESDAY WITH WEAK OFFSHORE FLOW DEVELOPING BEHIND THE TROF  
  AND BUILDING HIGH PRESSURE ALOFT. LONG RANGE MODELS STILL NOT  
  SHOWING ANY PRECIP THROUGH THE END OF THE MONTH. 
   
  && 
   
  .AVIATION...17/1800Z 
   
  A WEAK AND RELATIVELY DRY MID/UPPER LEVEL TROUGH OF LOW PRESSURE  
  UPSTREAM WILL MOVE OVER THE AREA. MODERATE SOUTHWEST UPPER LEVEL  
  WINDS WILL BECOME MODERATE NORTHWEST WHILE LIGHT SOUTH AND SOUTHEAST  
  MID LEVEL WINDS BECOME LIGHT NORTH BY 18/18Z. A CATALINA EDDY IS  
  EXPECTED TO DEVELOP OVERNIGHT AND LIGHT SHALLOW SOUTH LOW LEVEL MAY  
  BECOME MOIST OVER THE BIGHT. A WEAK TO MODERATE ONSHORE PRESSURE  
  GRADIENT WILL DEVELOP IN THE AFTERNOON...OTHERWISE A WEAK PRESSURE  
  GRADIENT WILL EXIST.       
   
  KLAX...THERE IS A CHANCE 1/2SM FG WILL DEVELOP BY 18/11Z AND LINGER  
  THROUGH 18/18Z...OTHERWISE CURRENT SKY/VSBY CONDITIONS WILL  
  CONTINUE.  
   
  KBUR...VERY LIKELY CURRENT SKY/VSBY CONDITIONS WILL PERSIST.  
   
  VIRTUALLY CERTAIN - 95-100% 
  VERY LIKELY       - 80-95% 
  LIKELY            - 60-80% 
  CHANCE            - 30-60% 
  VERY UNLIKELY     - 20% OR LESS 
   
   
  ***NOTE*** 
  THE ASOS EQUIPMENT AT KBUR...KVNY...KHHR...KCMA...AND KOXR HAS A  
  SOFTWARE ERROR THAT MAY LEAD TO INCORRECT CLOUD HEIGHTS WHEN THERE  
  ARE TWO OR MORE CLOUD LAYERS PRESENT. OBSERVATIONS AT KBUR WILL BE  
  QUALITY CONTROLLED 24 HOURS A DAY...OBSERVATIONS AT KVNY WILL BE  
  QUALITY CONTROLLED FROM 13Z-07Z...OBSERVATIONS AT KOXR WILL BE  
  QUALITY CONTROLLED FROM 15Z-05Z. TAFS FOR KVNY AND KOXR WILL NOT BE  
  AMENDED FOR CIGS DURING THE TIME THE OBSERVATIONS ARE NOT MONITORED  
  AND THERE ARE TWO OR MORE CLOUD LAYERS PRESENT. 
   
  && 
   
  .LOX WATCHES/WARNINGS/ADVISORIES... 
  SMALL CRAFT ADVISORY (SEE LAXMWWLOX). 
  HIGH SURF ADVISORY (SEE LAXCFWLOX). 
  HIGH RIP CURRENT RISK (SEE LAXSRFLOX). 
   
  && 
   
  
 
   
  PUBLIC...WOFFORD 
  AVIATION...30 
  SYNOPSIS...HOFFER 
   
  WWW.WEATHER.GOV/LOSANGELES