000
FXUS66 KLOX 142350 AAA
AFDLOX

SOUTHWEST CALIFORNIA AREA FORECAST DISCUSSION...UPDATE
NATIONAL WEATHER SERVICE LOS ANGELES/OXNARD CA
450 PM PDT SUN SEP 14 2008

UPDATE FOR NEW AVIATION DISCUSSION

.SHORT TERM (TODAY-WED)...INVERSION IS LOWERING AS HIGH PRESSURE
BUILDS OVER THE STATE. MARINE LYR DEPTH THIS MORNING WAS AROUND 1800
FT AND THIS IS EXPECTED TO DROP ABOUT IN HALF TONIGHT. IN ADDITION,
ONSHORE FLOW IS WEAKER TODAY AS SURFACE HIGH PRESSURE INCREASES
INLAND. THE RESULT WILL BE MUCH LESS OF AN INLAND PUSH OF THE LOW
CLOUDS TONIGHT AND AN EARLIER BURN OFF ON MONDAY. DAYTIME TEMPS WILL
ALSO INCREASE BY SEVERAL DEGREES IN MOST AREAS, ESPECIALLY THE
VALLEYS WHERE TEMPS HAVE BEEN KEPT IN CHECK BECAUSE OF THE MARINE
INFLUENCE.

BOTH THE NAM AND GFS SHOW THE OFFSHORE FLOW INCREASING TUESDAY WHILE
THE AIRMASS REMAINS VERY WARM. IF THIS COMES TO FRUITION, HIGHS ON
TUESDAY AT LOWER ELEVATIONS SHOULD BE 5-8 DEGREES WARMER THAN
MONDAY, PUSHING WARMER VALLEY HIGHS WELL ABOVE 100 AND DOWNTOWN LA
IN THE MID 90S. HOWEVER, THE MODELS HAVE BEEN CONSISTENT SHOWING AN
UPPER LOW OFF THE COAST OF NRN CA WITH A TROF EXTENDING SOUTH
TOWARDS SRN CA. IT`S UNUSUAL TO HAVE OFFSHORE GRADIENTS OF -2 MB
LAX-DAG AND 950 TEMPS NEAR 32C ACROSS THE LA BASIN WITH A TROF ALONG
THE COAST. MOS GUIDANCE HIGHS HAVE BEEN RUNNING ON THE COOL SIDE FOR
TUE POSSIBLY DUE TO THE TROF. BUT GENERALLY SPEAKING THE COMBINATION
OF THE OFFSHORE FLOW AND VERY WARM LOW LVL TEMPS WOULD RESULT IN
HIGHS TOPPING 100 IN THE VALLEYS AND IN THE 90S ACROSS THE INLAND
COASTAL PLAIN. WILL KEEP HIGHS WELL ABOVE MOS FOR NOW.

MODELS ALSO SHOW A VERY THIN LAYER OF MID LEVEL MOISTURE BEING
PULLED UP FROM THE SOUTH ON TUESDAY. THERE ISN`T ENOUGH MOISTURE TO
WARRANT ADDING CONVECTION TO THE FORECAST, BUT WITH LI`S DROPPING
BELOW ZERO IN THE LA COUNTY MOUNTAINS AND SURFACE TEMPS RISING WELL
INTO THE 90S WE COULD SEE SOME AFTERNOON CLOUDS ACROSS THE INTERIOR.
WILL GO WITH PARTLY CLOUDY INLAND TUESDAY AFTERNOON WITH POPS AT OR
BELOW 10 AND CLEAR ELSEWHERE.

OFFSHORE FLOW TURNS ONSHORE WEDNESDAY, BUT WEAK ENOUGH SO THAT
CLOUDS SHOULD REMAIN OUT OF THE VALLEYS. HOWEVER, COOLER MARINE AIR
WILL BRING DAYTIME HIGHS DOWN SEVERAL DEGREES AT LOWER ELEVATIONS
WITH TEMPS IN THE MOUNTAINS AND DESERTS ALSO COOLING DUE TO LOWER
THICKNESSES.

.LONG TERM (THU-SUN)...COOLING TREND TO CONTINUE THROUGH THURSDAY
BRINGING DAYTIME HIGHS DOWN TO NEAR NORMAL LEVELS. THEN LITTLE
CHANGE EXPECTED FRIDAY. OVER THE WEEKEND THE TROF FINALLY MOVES
INLAND THROUGH THE PAC NW AND HEIGHTS/THICKNESSES RISE SLIGHTLY
ACROSS SRN CA. ONSHORE FLOW ALSO WEAKENS, ESPECIALLY BY SUNDAY SO WE
COULD SEE A FEW DEGREES OF WARMING NEXT WEEKEND. FOR NOW THOUGH
CONFIDENCE ISN`T HIGH ENOUGH TO GO AGAINST PERSISTENCE SO WILL STICK
WITH SIMILAR CONDITIONS THROUGH THE WEEKEND.

&&

.AVIATION...14/2340Z...MARINE LAYER HAS FALLEN TO NEAR 1200 FT DEEP
AT KLAX. WITH THE MARINE LAYER EXPECTED TO CONTINUE LOWERING SOME
OVERNIGHT IT LOOKS LIKE LOW CLOUDS SHOULD NOT MOVE INTO THE VALLEY
TAF SITES TONIGHT AND MON. IT LOOKS LIKE MODERATE CONFIDENCE THAT
LOW CLOUDS AND IFR TO LIFR CONDITIONS WILL EVENTUALLY MOVE BACK INTO
MOST COASTAL TAF SITES TONIGHT. THE TIMING IS PROBLEMATIC
CONSIDERING THE CLEARING PATTERN OF THE LOW CLOUDS THIS AFTERNOON
OFF THE CENTRAL COAST AND THE CLEARING TREND ALONG THE COAST S OF
POINT CONCEPTION. OVERALL...MOST COASTAL TAF SITES SHOULD HAVE THE
LOW CLOUDS AND FOG MOVE IN FROM ABOUT 05Z TO 07Z. THE LOW CLOUDS AND
FOG WITH IFR AND SOME LIFR CONDITIONS WILL PREVAIL UNTIL ABOUT 16Z
TO 17Z MON...THEN VFR CONDITIONS SHOULD DEVELOP FROM LATER MON
MORNING THRU THE AFTERNOON. MODERATE TO HI CONFIDENCE THE TAF SITES
AWAY FROM THE COAST WILL HAVE VFR CONDITIONS THRU MON.

FOR KLAX...MODERATE CONFIDENCE IFR CIGS WILL MOVE INTO THE AIRFIELD
AROUND 06Z...BUT COULD BE DELAYED UNTIL 07Z OR 08Z. THE LOW CLOUDS
WILL CLEAR OFF THE COAST TO VFR CONDITIONS BY ABOUT 16Z MON...THEN
CLEAR CONDITIONS WILL PREVAIL THRU MON AFTERNOON. NO WIND ISSUES
EXPECTED THRU MON.

FOR KBUR...MODERATE CONFIDENCE VFR CONDITIONS WILL PREVAIL THROUGH
MON. NO WIND ISSUES ARE EXPECTED THRU THE PERIOD.

&&

.LOX WATCHES/WARNINGS/ADVISORIES...
RED FLAG WARNING (SEE LAXRFWLOX).
FIRE WEATHER WATCH (SEE LAXRFWLOX).
SMALL CRAFT ADVISORY (SEE LAXMWWLOX).

&&

$$

PUBLIC...WOFFORD
AVIATION...SIRARD

WWW.WEATHER.GOV/LOSANGELES