255 
FXUS66 KLOX 230007 AAA
AFDLOX

SOUTHWEST CALIFORNIA AREA FORECAST DISCUSSION...UPDATE
NATIONAL WEATHER SERVICE LOS ANGELES/OXNARD CA
510 PM PDT WED JUN 22 2011

***UPDATE FOR NEW AVIATION DISCUSSION***

.SYNOPSIS...

A WEAK UPPER-LEVEL LOW PRESSURE AREA MOVING OVER THE PACIFIC
NORTHWEST WILL STRENGTHEN ONSHORE FLOW...DEEPEN THE MARINE
LAYER...AND PROVIDE A COOLING TREND THROUGH FRIDAY. SOUTHWEST
FLOW ALOFT OVER THE AREA WILL KEEP AN ONSHORE FLOW IN PLACE
THROUGH MID-WEEK NEXT WEEK.

&&

.SHORT TERM (TONIGHT-SATURDAY)...

SURFACE PRESSURE GRADIENTS ARE TRENDING MORE STRONGLY ONSHORE THIS
AFTERNOON AND TRENDING THE DIRECTION THAT THE FORECAST PACKAGE
TAKES. ONSHORE FLOW WILL STRENGTHEN AHEAD OF AN APPROACHING UPPER-
LEVEL TROUGH OF LOW PRESSURE MOVING INTO BRITISH COLUMBIA AND THE
PACIFIC NORTHWEST. A COOLING TREND WILL BECOME MORE PRONOUNCED AS
ONSHORE FLOW STRENGTHENS AND THE MARINE LAYER DEEPENS. THE MARINE
LAYER NEAR 1200 FEET THIS AFTERNOON SHOULD DEEPEN TO AROUND 1800
FEET TONIGHT...THEN DEEPEN FURTHER TO FRIDAY. WITH MODEL
SOLUTIONS HANDLING THE LOW-LEVEL MOISTURE POORLY AND 1000-500 MB
THICKNESS VALUES SHRINKING...THE MARINE LAYER SHOULD DEEPEN TO
NEAR 2500 FEET BY FRIDAY. SOME LOWER COASTAL SLOPE INTRUSION
CANNOT BE RULED OUT AT THIS TIME...ESPECIALLY ON FRIDAY AND/OR
SATURDAY MORNING.

WITH ONSHORE GRADIENTS LIKELY TIGHTENING...THE COASTAL AND VALLEY
AREAS MAY BE DIFFICULT TO CLEAR ON FRIDAY...AND MAYBE SATURDAY.
THE EXCEPTION TO THIS PREMISE WILL BE THE INTERIOR VALLEYS OF SAN
LUIS OBISPO COUNTY AND THE ANTELOPE VALLEY. OUT IN THE ANTELOPE
VALLEY...SOUTHWEST WINDS WILL INCREASE TO NEAR ADVISORY
LEVEL...BUT AT THIS TIME...NO ADVISORY CONDITIONS ARE FORECAST.

A WEAK COOL FRONTAL BOUNDARY SHOULD EXIT THE REGION BY SATURDAY.
SATURDAY WILL LIKELY FALL INTO A REVERSE CLEARING DAY AS COLD AIR
ADVECTION SCOURS OUT THE MARINE LAYER AT THE COASTS BEFORE THE
VALLEYS. THE PACKAGE GENERALLY WARMS TEMPERATURES AT THE COASTAL
AREAS SATURDAY DUE TO BETTER CLEARING...WHILE COOLING THE VALLEYS
AND INTERIOR PORTIONS A LITTLE FURTHER.

.LONG TERM (SUNDAY-WEDNESDAY)...

SOUTHWEST FLOW ALOFT WILL REMAIN OVER THE AREA FOR EARLY NEXT WEEK
AS THE AREA WILL LIKELY REMAIN SANDWICHED BETWEEN THE UPPER-LEVEL
RIDGE OVER THE CHIHUAHUAN DESERT AND THE TROUGH OVER THE EASTERN
PACIFIC OCEAN. A PERSISTENT MARINE LAYER AND ONSHORE FLOW SHOULD
REMAIN IN PLACE OVER THE AREA THROUGHOUT THE LONG TERM PERIOD.
TEMPERATURES FOR THE PERIOD WERE WARMED SLIGHTLY FOR THE COASTS
AND VALLEYS...AND NUDGED CLOSER TO CLIMATOLOGY FOR THE INTERIOR
VALLEYS...MOUNTAINS...AND DESERT.

GFS AND ECMWF MODELS ARE IN PRETTY GOOD AGREEMENT THROUGH AT LEAST
MONDAY...BUT A COOLING TREND COULD DEVELOP AFTER NEXT TUESDAY.
ONSHORE GRADIENTS SHOULD STRENGTHEN BETWEEN NEXT TUESDAY AND
NEXT WEDNESDAY...AND TEMPERATURES WERE TRENDED COOLER FOR THE END
OF THE PERIOD.

&&

.AVIATION...23/0005Z...GENERALLY HI CONFIDENCE IN THE CURRENT TAF 
PACKAGE. MARINE LAYER CLOUDS WITH IFR/LIFR CONDITIONS WILL LINGER OR 
MOVE INTO THE COASTAL AND ADJACENT VALLEY AIRFIELDS FROM EARLY THIS 
EVENING TO LATER TONIGHT THEN PERSIST UNTIL MID MORNING TO AROUND 
MIDDAY THU...EXCEPT THE LOW CLOUDS SHOULD LINGER INTO LATE THU 
AFTERNOON AT KSBA AND KOXR. ELSEWHERE...VFR CONDITIONS ARE EXPECTED 
TONIGHT THRU THU.
 
KLAX...GENERALLY HI CONFIDENCE IN THE CURRENT TAF. LOW CLOUDS AND 
IFR/MVFR CONDITIONS ARE EXPECTED PREVAIL AT THE AIRFIELD THROUGH 
ABOUT 19Z THU. VFR CONDITIONS ARE EXPECTED THU AFTERNOON...WITH LOW 
CLOUDS AND MVFR CONDITIONS MOVING BACK IN BY 03Z THU EVENING.

KBUR...GENERALLY HI CONFIDENCE IN THE CURRENT TAF. VFR CONDITIONS 
CAN BE EXPECTED MOST OF THE TIME FROM TONIGHT THRU THU...EXCEPT FOR 
A PERIOD OF IFR CONDITIONS FROM AROUND 12Z-17Z...AND MVFR VSBYS 
17Z-21Z.

&&

.LOX WATCHES/WARNINGS/ADVISORIES...
SMALL CRAFT ADVISORY (SEE LAXMWWLOX).

&&

$$

PUBLIC...HALL
AVIATION...SIRARD
SYNOPSIS...HALL

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