000
FXUS66 KLOX 171657
AFDLOX

SOUTHWEST CALIFORNIA AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LOS ANGELES/OXNARD CA
955 AM PDT WED SEP 17 2008

.SHORT TERM (TODAY-FRI)...MARINE LAYER RANGED THIS MORNING FROM 1400
FT DEEP AT LAX TO NEAR 2200 FT AT VBG. LOW CLOUDS OVER MANY VALLEY
AND COASTAL AREAS WERE CLEARING RATHER QUICKLY BACK TO THE COAST
THROUGH MID MORNING. SOME LOW CLOUDS MAY LINGER AT THE BEACHES S OF
POINT CONCEPTION THIS AFTERNOON...OTHERWISE MOST OF THE LOW CLOUDS
SHOULD CLEAR OFF THE COAST. MOISTURE COMING IN FROM THE S AT LOWER
TO MID LEVELS WILL BRING PARTLY CLOUDY SKIES TO PORTIONS OF VTU/L.A.
COUNTIES THIS AFTERNOON. THERE IS ALSO A SLIGHT CHANCE OF
THUNDERSTORMS THIS AFTERNOON AND EARLY EVENING IN THE MOUNTAINS OF
VTU/L.A. COUNTIES AND THE ANTELOPE VALLEY...ALTHO AN INVERSION AT
AROUND 15000 FT AS SHOWN ON MORNING SOUNDINGS MAY INHIBIT CONVECTION
TO SOME DEGREE. TEMPS TODAY ACROSS THE REGION WILL BE GENERALLY NEAR
NORMAL FOR MOST AREAS.

A BROAD SOUTHWESTERLY FLOW ALOFT WILL PREVAIL OVER THE FORECAST AREA
THROUGH FRI AS AN UPPER LEVEL TROF APPROACHES THE COAST. AT LOWER TO
MID LEVELS...THE FLOW WILL BE MORE SOUTHERLY WHICH WILL HELP TO
BRING IN SIGNIFICANT LOWER TO MID LEVEL MOISTURE FROM OFF THE BAJA
COAST MAINLY TO VTU/L.A. COUNTIES TONIGHT INTO EARLY THU. THE WRF IS
FORECASTING 850 MB DEWPOINTS TO INCREASE TO 12 TO 16 DEG C OVER THE
REGION...WITH PWAT VALUES INCREASING TO AS HIGH AS 1.6 INCHES ALONG
THE COAST. THE INCREASING MOISTURE AT 850 MB SHOULD HELP TO
DESTABILIZE THE LOWER ATMOSPHERE ABOVE THE MARINE LAYER TO THE MID
LEVELS...AS SHOWN IN WRF SHOWALTER INDEX CHARTS (AS LOW AT -3 ALONG
THE VTU/L.A. COASTAL AREAS TONIGHT). THE WRF IS FORECASTING K-INDEX
VALUES INCREASING TO 35 TO NEAR 40 TONIGHT FOR MUCH OF THE AREA. IN
ADDITION...THE GFS IS SUPPORTING THE IDEA OF INCREASING LOWER LEVEL
MOISTURE OVER THE REGION DURING THE PERIOD. IT LOOKS MORE AND MORE
LIKE THERE WILL BE THE POSSIBILITY OF A FEW SHOWERS AND EVEN AN
ISOLATED THUNDERSTORM OVER VTU/L.A. COUNTIES TONIGHT. THIS WILL
LIKELY BE REFLECTED IN THE AFTERNOON ZONE PACKAGE. FOR NOW HAVE
OPTED TO INTRODUCE PARTLY CLOUDY SKIES TO THE REGION FOR THIS
AFTERNOON AND TONIGHT. ALTHO SOME MID LEVEL MOISTURE SHOULD LINGER
THU...IT LOOKS LIKE THE THREAT OF AFTERNOON THUNDERSTORMS FOR THE
MTNS OF VTU/L.A. COUNTIES WILL BE MINIMAL AT BEST WITH JUST SOME CU
BUILDUPS POSSIBLE. MARINE LAYER CLOUDS MAY BE HARD PRESSED TO BECOME
ORGANIZED TONIGHT S OF POINT CONCEPTION...OTHERWISE PLENTY OF LOW
CLOUDS AND FOG NIGHT AND MORNING HOURS CAN BE EXPECTED THRU FRI FOR
THE COAST AND VALLEYS. HI TEMPS ARE FORECAST TO BE NEAR NORMAL FOR
THE MOST PART ON THU THEN COOL TO SLIGHTLY BELOW NORMAL FOR FRI.

...FROM PREVIOUS DISCUSSION...

.LONG TERM (FRI NIGHT-WED)...THE IMPULSE ON FRIDAY CONTINUES TO
FLUMMOX THE MEDIUM RANGE MODELS. SATURDAYS FORECAST LOOKS ON TRACK
WITH THE LOW MOVING OUT AND HGTS RISING THE MARINE LAYER SHOULD
SHRINK A LITTLE AND TEMPS SHOULD WARM A FEW DEGREES.

AFTER SATURDAY THE MDLS GO THEIR OWN WAYS AND THE GFS ENSEMBLES
BOMB-BURST INTO A SQUIGGLY MESS. WITH LITTLE OR NO CONFIDENCE IN THE
LONG RANGE FORECAST MADE A FEW ADJUSTMENT TOWARD CLIMATOLOGY BUT IN
GENERAL LEFT THINGS UNCHANGED FROM SUNDAY ON. HOPEFULLY THE MODELS
WILL GET A HANDLE ON FRIDAYS IMPULSE AND THE MEDIUM RANGE MDLS WILL
GET A HANDLE ON THINGS.

&&

.AVIATION...

17/1100Z

MARINE LAYER IS NEAR 1300 FEET AND PUSHED IN NICELY BY A 3 MB
GRADIENT. CIGS ARE HIGH ENOUGH TO MAKE IT INTO THE VLYS BUT WILL
ALSO BE HIGH ENOUGH TO NOT PRESENT MUCH OF VISIBILITY PROBLEM. THE
CENTRAL COAST WILL BE SLOW TO CLEAR. THE MARINE CLOUD PATTERN THIS
EVENING AND OVERNIGHT SHOULD BE VERY SIMILAR TO YDY NIGHT.

KLAX...VERY GOOD CONFIDENCE IN 12Z TAF. CIG CLEARING WILL VERY
LIKELY BE WITHIN AN HOUR OF FORECAST.

KBUR...GOOD CONFIDENCE IN TH 12Z TAF. CIG BURN OFF COULD BE ONE OR
TWO HOURS LATER THAN FORECAST. CIG ARRIVAL TONIGHT WILL BE AFTER
MIDNIGHT AND MORE LIKELY TOWARD DAWN.

&&

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

&&

$$

PUBLIC...SIRARD/RORKE
AVIATION...BRUNO

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