965 
FXUS66 KLOX 181923
AFDLOX

SOUTHWEST CALIFORNIA AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LOS ANGELES/OXNARD CA
1225 PM PDT TUE SEP 18 2012

...NEW AVIATION DISCUSSION...

.SYNOPSIS...
A WEAK HIGH WILL PERSIST OVER THE AREA THROUGH MUCH OF THE WEEK WITH 
DRY WEATHER AND TEMPERATURES RUNNING SEVERAL DEGREES ABOVE NORMAL 
AWAY FROM THE COAST. LOW PRESSURE WILL APPROACH BY THE WEEKEND WITH 
A GRADUAL COOLING TREND INTO EARLY NEXT WEEK. NIGHT AND MORNING LOW 
CLOUDS AND FOG ARE EXPECTED FOR COASTAL AND SOME VALLEY AREAS 
THROUGH THE PERIOD...OTHERWISE MOSTLY CLEAR SKIES WILL PREVAIL.
 
&&

.UPDATE...VISIBLE IMAGES AND SURFACE OBSERVATIONS INDICATE THAT 
PATCHY DENSE FOG AFFECTED THE NEAR-COASTAL PORTIONS OF THE L.A. AND 
VENTURA COUNTIES EARLIER THIS MORNING...WITH VISIBILITY LESS THAN 
1/4 MILE IN SOME LOCATIONS. ACARS SOUNDINGS AT KLAX SHOW A MARINE 
LAYER DEPTH NEAR 800 FEET FORMING AFTER AROUND 13 UTC. AT THE TIME 
OF THIS UPDATE...MOST OF THE LOWER VISIBILITIES HAVE DISSIPATED WITH 
PATCHY LOW CLOUDS LINGERING. NORTH OF PT CONCEPTION...THE MARINE 
LAYER DEPTH WAS 1800 FEET WITH CLOUD BASES AROUND 600 FEET ALONG THE 
COAST AND NEAR 200 FEET OVER THE SALINAS VALLEY. 

WITH A FAIRLY STABLE SYNOPTIC PATTERN IN PLACE...EXPECT LITTLE 
CHANGE IN AREA WEATHER CONDITIONS THROUGH THURSDAY. HEIGHTS ALOFT 
WILL REMAIN NEAR 588 DM...WITH SURFACE GRADIENTS SLOWLY TRENDING 
FROM WEAKLY ONSHORE TO WEAKLY OFFSHORE. THE OVERNIGHT MARINE STRATUS 
PATTERN WILL CHANGE LITTLE THROUGH THE PERIOD...COVERING THE CENTRAL 
COAST AND SANTA YNEZ VALLEY N OF POINT CONCEPTION. LOW CLOUDS/FOG 
WILL MOST LIKELY AFFECT THE SALINAS VALLEY AGAIN TONIGHT BUT SHOULD 
REMAIN CLEAR AFTER THAT. SOUTH OF POINT CONCEPTION...EXPECT A REPEAT 
OF LOW CLOUDS AND PATCHY DENSE FOG OVER THE PALOS VERDES PENINSULA 
AND THE VENTURA BEACHES LATE TONIGHT INTO EARLY WEDNESDAY MORNING. 
AS GRADIENTS SHIFT TO OFFSHORE THE LOW CLOUDS WILL BECOME LESS 
EXTENSIVE WEDNESDAY NIGHT...MOST LIKELY LIMITED TO THE L.A. BEACHES. 

TEMPERATURES WILL REMAIN NEAR-NORMAL FOR COASTAL AREAS...AND 
SLIGHTLY ABOVE NORMAL INLAND. EXPECT A VERY SLOW WARMING TREND 
THROUGH THE SHORT TERM FOR THE VALLEYS...WITH AFTERNOON HIGHS IN THE 
MID TO UPPER 90S BY THURSDAY. 

.SHORT TERM (TODAY-THU)...
THREE VERY SIMILAR DAYS ON TAP IN THE SHORT TERM. A WEAK RIDGE 
EXTENDING UPWARDS FROM AN UPPER HIGH TO THE SSW WILL PERSIST THROUGH 
THE PERIOD. HGTS WILL BE ABOUT 599 DM THRU THE PERIOD. GRADIENTS 
WILL STAY WEAKLY ONSHORE AND FOLLOW A TYPICAL DIURNAL TREND. MAX 
TEMPS WILL REMAIN NEAR NORMAL ACROSS THE COAST AND A FEW DEGREES 
ABOVE NORMAL INLAND. MARINE LAYER STRATUS WILL COVER THE CENTRAL 
COAST AND SANTA YNEZ VLY DURING THE NIGHT THROUGH MORNING HOURS. THE 
STRATUS SITUATION IS FAR MURKIER SOUTH OF POINT CONCEPTION. 
CURRENTLY SOME STRATUS IS FORMING OFF OF THE L.A. COAST AND THAT 
SHOULD BE IT FOR TODAY. TRIMMED BACK THE STRATUS COVERAGE FOR THE 
NEXT TWO NIGHTS AS WELL BUT MAY HAVE NOT REDUCED IT ENOUGH.

.LONG TERM (FRI-MON)...
ACTUAL OFFSHORE FLOW SETS UP FRIDAY AND SHOULD MAKE IT THE WARMEST 
DAY OF THE NEXT SEVEN AS WELL AS THE MOST STRATUS FREE.

ALL MDLS AGREE THAT AN UPPER LOW WILL SWING INTO CALIFORNIA OVER THE 
WEEKEND. ALL MDLS DISAGREE IN LOCATION AND TIMING AND STRENGTH. THE 
GFS BRINGS A GOOD SLUG OF MOISTURE WITH THE TROF ASSOC WITH THE 
UPPER LOW WHEN IT PASSES OVER SOCAL. THE OTHER MDLS ARE DRY AND 
GIVEN THE 582 DM HGTS FAVOR THE DRY SOLN. WENT WITH A DRY FCST WITH 
A DEEP AND ROBUST MARINE LAYER AS WELL AS A GOOD COOLING TREND.

THE UPPER LOW SHOULD BE SOMEWHERE OVER THE STATE NORTHERN TWO THIRDS 
OF THE STATE ON MONDAY. THE DEEP STRATUS PATTERN WILL PERSIST WITH 
FURTHER COOLING LIKELY.

&&

.AVIATION...18/1800Z.
WITH DECREASING ONSHORE FLOW EXPECTED OVER THE NEXT 24 HOURS...THE 
PRESENCE OF FOG AND LOW CLOUDS SOUTH OF POINT CONCEPTION GETS CALLED 
INTO QUESTION. THEREFORE...THE 18Z TAF FORECAST HAS LOW CONFIDENCE 
IN REGARDS TO FOG AND LOW CLOUDS IN THE COASTAL SECTIONS SOUTH OF 
POINT CONCEPTION. ELSEWHERE...GOOD CONFIDENCE IN THE 18Z TAFS.

KLAX...LOW CONFIDENCE IN THE 18Z TAF. THERE IS A 40 PERCENT CHANCE 
OF VFR CONDITIONS THROUGH THE NIGHT. OTHERWISE IFR CONDITIONS ARE 
CURRENTLY EXPECTED TO DEVELOP OVERNIGHT.

KBUR...HIGH CONFIDENCE IN VFR CONDITIONS THROUGH WEDNESDAY.

&&

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

&&

$$

PUBLIC...RORKE/SMITH
AVIATION...SWEET
SYNOPSIS...SIRARD

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