000
FXUS66 KLOX 142045
AFDLOX

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

.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...14/1730Z
MARINE LAYER DEPTH FAIRLY UNIFORM THIS MORNING...CURRENTLY AROUND
1800 FEET. MODEL CROSS SECTIONS CONTINUE TO ADVERTISE A WEAKENING OF
THE ONSHORE FLOW LATER TONIGHT AND MONDAY...WITH A CORRESPONDING
SHARP REDUCTION OF THE MARINE LAYER DEPTH. BY MONDAY MORNING...WOULD
EXPECT MARINE LAYER DEPTH TO BE LESS THAN 1000 FEET IN MOST
AREAS...BRINGING THE POTENTIAL FOR IFR/LIFR CONDITIONS TO COASTAL
TAF LOCATIONS...WITH A MORE RAPID CLEARING TREND EXPECTED MONDAY
MORNING.

KLAX...WITH SATELLITE IMAGERY SHOWING A SOLID BLANKET OF OVERCAST
ACROSS THE LA COASTAL PLAIN...WOULD EXPECT CEILING TO LINGER TO
AROUND 21Z AT KLAX. WITH MARINE LAYER DEPTH AROUND 1500 FEET LATER
THIS AFTERNOON AND EVENING...THERE WILL BE THE POTENTIAL FOR SOME
SEA BREEZE STRATUS. PRETTY GOOD CONFIDENCE THAT A CEILING WILL
REDEVELOP OVERNIGHT...WITH TIMING MOST LIKELY BETWEEN 04Z-06Z. AT
THIS TIME...APPEARS THAT CEILING HEIGHTS WILL RANGE BETWEEN 300 AND
600 FEET.

KBUR...CEILING EXPECTED TO BURN OFF WITHIN NEXT HOUR OR SO...WITH
SOME HAZE LINGERING THROUGH EARLY AFTERNOON HOURS. WITH MARINE LAYER
BECOMING MORE SHALLOW OVERNIGHT...IT IS LIKELY THAT VFR CONDITIONS
WILL PREVAIL FOR REMAINDER OF PERIOD.

&&

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

&&

$$

PUBLIC...WOFFORD
AVIATION...GOMBERG

WWW.WEATHER.GOV/LOSANGELES