299 
FXUS66 KLOX 111859
AFDLOX

SOUTHWEST CALIFORNIA AREA FORECAST DISCUSSION 
NATIONAL WEATHER SERVICE LOS ANGELES/OXNARD CA
1155 AM PDT TUE SEP 11 2012

...NEW AVIATION DISCUSSION...

.SYNOPSIS...
SLIGHTLY COOLER WEATHER WILL AFFECT SOUTHWEST CALIFORNIA TODAY AND 
WEDNESDAY AS A WEAK TROUGH PASSES TO THE NORTH. EXPECT AFTERNOON 
CLOUD BUILDUPS OVER THE EASTERN MOUNTAINS BUT OTHERWISE MOSTLY CLEAR 
SKIES. ABOVE NORMAL TEMPERATURES ARE THEN EXPECTED THURSDAY THROUGH 
SUNDAY AS HIGH PRESSURE BUILDS OVERHEAD.

&&

.UPDATE...FORECAST IS ON TRACK TODAY WITH AN UPPER TROUGH OVER 
CENTRAL CALIFORNIA BRINGING A SOUTHWEST FLOW INTO THE AREA. GFS 
SHOWS A DRY AIR MASS AT MID TO UPPER LEVELS RAPIDLY MOVING INTO THE 
AREA...IN AGREEMENT WITH WATER VAPOR IMAGERY...WHICH SHOWS THE DRY 
AIR INTRUSION UNDERWAY. HOWEVER...THERE IS PLENTY OF MOISTURE STILL 
LINGERING AT LOW LEVELS THIS MORNING. MODELS SHOW THAT LOW LEVEL 
MOISTURE AND PRECIPITABLE WATER WILL BE DECREASING SLOWLY THROUGH 
THE DAY...SO WHILE SOME INSTABILITY PARAMETERS SHOW SOME POTENTIAL 
FOR AFTERNOON CONVECTION OVER THE MTNS OF VTU AND LA COUNTIES...AND 
EVEN TO SOME EXTENT OVER THE SBA MTNS...BELIEVE THAT MOISTURE WILL 
BE INSUFFICIENT TO PRODUCE ANYTHING OTHER THAN CUMULUS BUILDUPS. 

THE LOW CIRCULATION OVER BAJA IS WEAKENING AND SHIFTING EAST 
TODAY...WHILE ANOTHER WEAK TROUGH CONTINUES TO WEAKEN AS IT MOVES 
THROUGH CENTRAL CALIFORNIA AND INTO NEVADA. THE SECOND TROUGH HAS 
HELPED TO GENERATE MARINE LAYER CLOUDS N OR POINT CONCEPTION 
OVERNIGHT. THE ONSHORE FLOW OVER THE AREA IS ALSO CAUSING LOW CLOUDS 
TO APPROACH THE COASTLINE S OF POINT CONCEPTION TODAY...AND MAY KEEP 
CLOUDS NEAR/OVER THE BEACHES OF SBA...VTU AND LA FOR MUCH OF THE 
DAY. 

.FROM PREVIOUS DISCUSSION (TONIGHT-THU)...
STRONGER ONSHORE FLOW WILL BRING A BETTER MARINE LAYER TONIGHT AND 
STRATUS SHOULD COVER MOST OF THE COASTS BY WEDNESDAY MORNING. AN 
UPPER LEVEL HIGH WILL BUILD INTO CALIFORNIA DURING THE DAY AND 
RISING HGTS WILL WARM TEMPS...ESP INLAND.

THE HIGH CONTINUES TO BUILD ON THURSDAY. GOOD OFFSHORE TRENDS SET UP 
AS WELL AND THIS SHOULD LIMIT LOW CLOUDS TO JUST THE IMMEDIATE 
CENTRAL COAST. THE WARMING TREND WILL CONTINUE AND MOST AREAS AWAY 
FROM THE BEACHES WILL BE ABOVE NORMAL.

.LONG TERM (FRI-MON)...
MEDIUM RANGE MDLS AGREE THAT AN 590+ DM UPPER LEVEL HIGH WILL SIT 
ATOP OF THE STATE FROM FRIDAY THROUGH SUNDAY. THERE WILL ONLY BE A 
LIMITED MARINE LAYER ACROSS THE CENTRAL COAST. MAX TEMPS WILL BE 
WELL ABOVE NORMAL WITH WEAK OFFSHORE FLOW IN THE MORNING. FRIDAY 
SHOULD BE THE WARMEST DAY OF THE WEEK BUT SAT AND SUN WILL ONLY BE A 
COUPLE DEGREES COOLER AND STILL WELL ABOVE NORMAL.

ON MONDAY MDLS BEGIN TO DISAGREE BUT IT LOOKS LIKE THE RIDGE WILL BE 
PUSHED AWAY TO THE SOUTH AND WEST BY A VERY LARGE CYCLONIC FLOW 
PATTERN THAT WILL COVER MOST OF THE CONUS. THIS SHOULD KICK OFF A 
DECENT COOLING TREND.

&&

.AVIATION...11/1800Z.
A FAIRLY COMPLEX AVIATION FORECAST WITH RATHER POOR CONFIDENCE IN 
THE EVOLUTION OF CLOUD COVER. REMNANT MOISTURE IS INTERACTING WITH A 
WEAK TROUGH PUSHING ACROSS THE FORECAST AREA. LOW CLOUDS AND FOG 
HAVE RUSHED TO THE COAST AND WILL CONTINUE TO HARASS COASTAL TAF 
SITES THROUGH THE AFTERNOON...ESPECIALLY SOUTH OF POINT CONCEPTION. 
THE LOW CLOUDS AND FOG WILL CAUSE MVFR TO IFR CONDITIONS AS THEY 
SURGE INTO COASTAL SECTIONS FOR GOOD THIS EVENING. 

KLAX...SCT V BKN CONDITIONS THIS AFTERNOON THEN BKN TO OVC THIS 
EVENING THROUGH WED MORNING. MARINE CLOUDS WILL BRING MVFR TO IFR 
CONDITIONS. A LOW CONFIDENCE FORECAST FOR TIMING OF SCT VS BKN 
CONDITIONS. 

KBUR...GOOD CONFIDENCE IN VFR CONDITIONS THROUGH WEDNESDAY. THERE IS 
A 20 PERCENT CHANCE OF IFR CONDITIONS NEAR MORNING. 

&&

.LOX WATCHES/WARNINGS/ADVISORIES...
NONE

&&

$$

PUBLIC...RORKE
AVIATION...SWEET
SYNOPSIS...SUKUP

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