076 
FXUS66 KLOX 121623
AFDLOX

SOUTHWEST CALIFORNIA AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LOS ANGELES/OXNARD CA
920 AM PDT MON SEP 12 2011

.SYNOPSIS...

AN LOW PRESSURE SYSTEM WILL BRING ISOLATED SHOWERS AND THUNDERSTORMS 
TO THE AREA TODAY AND TUESDAY. NIGHT AND MORNING LOW CLOUDS WILL 
RETURN TO COASTAL AND VALLEY AREAS TUESDAY NIGHT AS THE LOW MOVES 
FURTHER EAST. ANOTHER LOW WILL MOVE ACROSS THE AREA LATE THURSDAY 
INTO FRIDAY...DEEPENING THE MARINE LAYER AND KEEPING TEMPERATURES 
BELOW SEASONAL NORMALS. 

&&

.SHORT TERM (TODAY-WED)...THE TROF REMAINS OVER SOUTHERN CALIFORNIA 
TODAY. AN EMBEDDED CIRCULATION IS DROPPING SOUTH INTO THE TROF 
OFFSHORE OF CENTRAL CALIFORNIA TODAY. IT MAY BE TOO FAR OFFSHORE TO 
POSE MUCH OF A THREAT TO THE COAST, BUT IT WILL DESTABILIZE THE AIR 
MASS ENOUGH, ESPECIALLY OVER THE INTERIOR, TO BRING A SLIGHTLY 
BETTER RISK FOR AFTERNOON CONVECTION THAN SUNDAY. THE INSTABILITY 
PARAMETERS AND AVAILABLE MOISTURE DEFINITELY FAVOR INTERIOR AREAS 
NORTH OF PT CONCEPTION. IN FACT, WE MAY SEE VERY LITTLE VERTICAL 
DEVELOPMENT OF CU ACROSS LA COUNTY TODAY. UPDATED THE DIGITAL 
FORECAST TO SHIFT EMPHASIS TO THE NORTHERN AREAS TODAY WHILE LEAVING 
IN JUST VERY LOW LVL POPS ACROSS LA COUNTY MTNS AND ANTELOPE VALLEY.

VBG AND NKX SOUNDINGS BOTH SHOW WARMING IN THE LOWER LEVELS AS THE 
MARINE INVERSION SHRUNK OVERNIGHT. THIS WAS EXPECTED. HOWEVER, WHAT 
WASN'T EXPECTED WAS THE COMPLETE EVACUATION OF LOW CLOUDS THAT 
OCCURRED SUNDAY AFTERNOON WITHOUT THE TYPICAL RETURN. EITHER WAY, WE 
EXPECTED TODAY WOULD BE WARMER AND THIS MORNING'S DEVELOPMENTS 
CERTAINLY DON'T CHANGE THAT IDEA. THERE IS A GOOD SOUTHWARD PUSH OF 
LOW CLOUDS OFF THE MONTEREY COUNTY COAST AND WE SHOULD SEE THOSE 
CLOUDS FILLING IN ACROSS THE CENTRAL COAST THIS AFTERNOON AND 
EVENING. FURTHER SOUTH HOWEVER WE SHOULD SEE ONE MORE DAY OF CLEAR 
SKIES OVERNIGHT. MODELS STILL SHOWING GRADIENTS TRENDING OFFSHORE 
TUESDAY SO A FEW MORE DEGREES OF WARMING EXPECTED TOMORROW.

***FROM PREVIOUS DISCUSSION***

THE UPPER LOW WILL BEGIN TO SHIFT EASTWARD ON TUESDAY...WITH SHOWERS 
AND THUNDERSTORMS EXPECTED TO LINGER OVER THE INTERIOR MOUNTAINS AND 
DESERTS TUESDAY AFTERNOON AND EVENING. WHILE THE LOW CENTER MOVES 
EASTWARD TOWARD THE 4 CORNERS REGION ON WEDNESDAY...THE UPPER TROUGH 
WILL CONTINUE TO EXTEND WESTWARD ACROSS SOUTHERN CALIFORNIA. 
MOISTURE AND INSTABILITY WILL BECOME MUCH MORE LIMITED PER NAM12 BUT 
THERE WILL LIKELY BE ENOUGH TO PRODUCE SOME CUMULUS DEVELOPMENT OVER 
THE INTERIOR SECTIONS.   

.LONG TERM (THU-SUN)...HEIGHTS ALOFT ARE FORECAST TO RISE BRIEFLY ON 
THURSDAY AS THE TROUGH SHIFTS FURTHER INLAND...BUT ANOTHER UPPER LOW 
WILL SWING ACROSS THE AREA THURSDAY NIGHT INTO FRIDAY. THIS WILL 
KEEP TEMPERATURES BELOW SEASONAL NORMALS...AND ALLOW FOR GOOD 
DEEPENING OF THE MARINE LAYER. MODEL AGREEMENT BEGINS TO DEGRADE 
FRIDAY INTO SATURDAY AS THE ECMWF BRINGS A STRONGER CUTOFF LOW DOWN 
THE COAST TO POINT CONCEPTION...WHILE THE GFS HAS A WEAKER OPEN WAVE 
SOLUTION. HOWEVER...THE IDEA OF TROUGHING OVER THE AREA WILL 
MAINTAIN A DEEP MARINE LAYER THROUGH SATURDAY MORNING ALONG WITH 
LOWER DAYTIME HIGHS ACROSS INTERIOR SECTIONS. BOTH MODELS SHOW THE 
LOW EDGING EASTWARD ON SUNDAY...ALLOWING FOR WARMING INLAND AND A 
SLIGHT SUPPRESSION OF THE MARINE LAYER. 

&&

.AVIATION...

12/1140Z

VERY GOOD CONFIDENCE IN 12Z TAF PACKAGE THROUGH THIS EVENING. THERE 
IS A 20 PERCENT CHC OF TSTMS OVER THE MTNS AND DESERTS AS WELL AS 
SAN LUIS OBISPO AND SANTA BARBARA COUNTIES.

KLAX...VERY GOOD CONFIDENCE IN TAF THROUGH 08Z. A 30 PERCENT CHANCE 
OF IFR CIGS AFTER 08Z.

KBUR...VERY GOOD CONFIDENCE IN CAVU TAF.

&&

.LOX WATCHES/WARNINGS/ADVISORIES...
NONE.

&&

$$

PUBLIC...WOFFORD/BRUNO/SMITH
AVIATION...ASR
SYNOPSIS...SIRARD

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