000
FXUS66 KLOX 141742
AFDLOX

SOUTHWEST CALIFORNIA AREA FORECAST DISCUSSION...UPDATED
NATIONAL WEATHER SERVICE LOS ANGELES/OXNARD CA
1045 AM PDT SUN SEP 14 2008

UPDATED AVIATION SECTION

.SHORT TERM (TODAY-TUE)...MARINE LYR HAS DECREASED TO ABOUT 1800 FT
THIS MORNING AS HIGH PRESSURE BUILDS OVER THE STATE. ONSHORE IS ALSO
WEAKER THIS MORNING. THE SIMI VALLEY PROFILER IS SHOWING 5-10
DEGREES OF WARMING ABOVE THE MARINE LYR SO EXPECT FOOTHILLS AND
MOUNTAINS ALONG WITH THE SANTA CLARITA VALLEY TO SEE MUCH WARMER
TEMPS TODAY. THE AMOUNT OF WARMING TODAY WILL DECREASE TOWARDS THE
COAST AND EXPECT LITTLE CHANGE IN TEMPS AT THE BEACHES TODAY WITH
SOME CLOUDS AGAIN LINGERING THROUGH THE AFTERNOON.

NOT TOO MUCH CHANGE IN THE 12Z MODELS FOR MON AND TUE. BOTH THE GFS
AND NAM SHOW GRADIENTS TURNING OFFSHORE MONDAY MORNING, WITH THE
OFFSHORE FLOW STRENGTHENING TUESDAY MORNING. WITH 950 TEMPS EXPECTED
TO BE CLOSE TO 30C COMBINED WITH THE OFFSHORE FLOW TEMPS AT ALL
LOWER ELEVATION LOCATIONS SHOULD SEE IMPRESSIVE GAINS MONDAY AND
AGAIN TUESDAY. MOS GUIDANCE VALUES FOR TUESDAY SEEM WAY TOO LOW
GIVEN THE OFFSHORE FLOW AND CURRENT FORECAST NUMBERS ARE SEVERAL
DEGREES HIGHER. LOCAL TEMPERATURE GUIDANCE EVEN INDICATES HIGHS ON
TUE COULD EVEN BE WARMER THAN CURRENTLY INDICATED IF ALL FACTORS
COME TOGETHER AS CURRENTLY PROJECTED.

12Z MODELS SHOWED A NARROW BAND OF MOISTURE AROUND 700 MB FOR TUE
DUE TO THE INFLUENCE OF THE UPPER LOW OFF NRN CALIFORNIA. HOWEVER,
IT`S STILL VERY DRY AT LOWER LEVELS. NAM DID SHOW LI`S DROPPING
BELOW ZERO TUESDAY AFTERNOON OVER ERN LA COUNTY. FOR NOW HAVE
CONFINED AFTERNOON CLOUDS TO THE INTERIOR PORTION OF THE CWA. IF ANY
CONVECTION DOES DEVELOP IT LOOKS LIKE IT WOULD BE OVER ERN LA
COUNTY. BUT CHANCES ARE TOO LOW TO PUT IN THE FORECAST FOR NOW.

*** LONG TERM FROM PREVIOUS DISCUSSION ***

.LONG TERM...
EC AND GFS IN GOOD AGREEMENT THROUGH SATURDAY AND THEN DIVERGE. GFS
ENSEMBLES POINT TO A LOWER CONFIDENCE FORECAST STARTING FRIDAY BUT
MOST OF THE ENERGY IS WELL NORTH OF US AND NOT TOO SURE HOW MUCH THE
DEVIATIONS WILL AFFECT THE WEATHER DOWN HERE. IN SHORT THERE IS
LIKELY GOING TO BE TROFING THROUGH AT LEAST FRIDAY WITH A PM/AM
CLOUD PATTERN AND TEMPS A LITTLE COOLER THAN NORMAL. A SMALL RIDGE
WILL BUILD IN LATER FRIDAY AND SATURDAY PROBABLY TOO LATE TO AFFECT
THE MARINE LAYER OR COASTAL TEMPS SATURDAY MUCH BUT INLAND TEMPS MAY
RISE A FEW DEGREES SATURDAY.

&&

.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...
SMALL CRAFT ADVISORY (SEE LAXMWWLOX).
FIRE WEATHER WATCH (SEE LAXRFWLOX).

&&

$$

PUBLIC...WOFFORD/RORKE
AVIATION...HALL

WWW.WEATHER.GOV/LOSANGELES