000
FXUS66 KLOX 080319
AFDLOX
SOUTHWEST CALIFORNIA AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LOS ANGELES/OXNARD CA
819 PM PDT SUN SEP 7 2008
.UPDATE...MARINE LAYER MAKING FAIRLY AGGRESSIVE RETURN TONIGHT.
MAJORITY OF COASTAL WATERS ARE ALREADY COVERED WITH STRATUS
CLOUDS. LATEST ACARS SOUNDINGS PLACE MARINE LAYER INVERSION NEAR
1100 FEET THIS EVENING AND THE MARINE LAYER SHOULD DEEPEN SLIGHTLY
THROUGHOUT TONIGHT AS A DEVELOPING WEAK TROUGH CONTINUES TO DIG
SOUTH...AND INTERACTS WITH THE WEAK EDDY CIRCULATION IN PLACE
SOUTH OF POINT CONCEPTION. NAM-WRF TIME HEIGHT SECTIONS INDICATE
SLIGHT LIFTING OF THE MARINE LAYER FOR AREAS SOUTH OF POINT
CONCEPTION THROUGHOUT TONIGHT. THE MARINE LAYER SHOULD PUSH INTO
THE LOS ANGELES AND VENTURA COUNTY VALLEY AREAS LATER TONIGHT.
ALONG THE CENTRAL COAST...LOWER CONFIDENCE EXISTS IN THE LIFTING
ALTHOUGH GRADIENTS ARE STARTING TO INDICATE THE POSSIBILITY FOR
DENSE FOG NOT FORMING OVER THE AREA. CURRENT PACKAGE LEAVES OUT
THE MENTION OF DENSE FOG...ALTHOUGH GFS AND ETA MOS GUIDANCE FOR
KSMX AND KSBP CONTINUES TO SUGGEST IT. FOR NOW...ANY UPDATES WILL
DELAYED FOR FURTHER CLARITY WITH ARRIVING MARINE LAYER.
SOME CONCERN IS DEVELOPING FOR AN ISOLATED SHOWER OR THUNDERSTORM
OVER THE SAN GABRIEL RANGE AND THE ANTELOPE VALLEY ALONG THE LOS
ANGELES-SAN BERNARDINO BORDER ON MONDAY. THOUGH MOISTURE PATTERN
IS NOT IMPRESSIVE...850-700 MB MIXING RATIO AROUND 6 G/KG DEVELOP
OVER THE SAN GABRIEL RANGE AND THE EASTERN PORTION OF THE ANTELOPE
VALLEY WHICH COULD BE ENOUGH FOR POSSIBLE PRECIPITATION. 700-500
MB RELATIVE HUMIDITIES INCREASE AND NAM-WRF SOLUTIONS DEVELOP SOME
MID-LEVEL CAPE OVER THE AREA FOR MONDAY AFTERNOON AND EVENING. IN
ADDITION...A FAIR AMOUNT OF 500 MB DIVERGENCE IS PRESENT IN A WEAK
SOUTHEAST FLOW PATTERN. GFS HAS SIMILAR SIGNATURES IN THE 18Z
SOLUTIONS BUT PUSHES THE AREA OF INSTABILITY OVER THE AREA ABOUT 3
TO 6 HOURS EARLIER IN THE DAY ON MONDAY. WITH GOOD INSTABILITY BUT
A LACK OF MOISTURE...FOR NOW...AN UPDATE WILL BE PERFORMED TO
INCREASE CLOUD COVER OVER THE MOUNTAINS AND DESERT FOR MONDAY
AFTERNOON AND EVENING AND THE NEXT SHIFT WILL BE BRIEFED ABOUT
PRECIPITATION POSSIBILITIES.
THE TROUGH DIGGING SOUTH INTO NORTHERN CALIFORNIA WILL STALL OUT
OVER NORTHERN CALIFORNIA ON MONDAY. THEN...A SECONDARY WAVE DROPS
IN BEHIND AND KICKS THE TROUGH SOUTH FOR MIDWEEK. BETTER MODEL
AGREEMENT IS DEVELOPING FOR MIDWEEK WITH BETTER COOLING POSSIBLE
FOR TUESDAY AND WEDNESDAY. COOLING TREND EXISTS IN THE CURRENT
PACKAGE...BUT TEMPERATURES COULD BE SLIGHTLY COOLER OVER THE
INTERIOR THAN WHAT THE CURRENT PACKAGE SUGGESTS...ESPECIALLY THE
MOUNTAINS. NAM-WRF AND GFS 850 MB TEMPERATURES COOL THROUGH
WEDNESDAY AFTERNOON...WHILE THE PACKAGE PROVIDE SIMILAR
TEMPERATURES FOR TUESDAY AND WEDNESDAY...SO ADDITIONAL COOLING
MAY BE NEEDED IN THE PACKAGE.
&&
.PREV DISCUSSION... /ISSUED 115 PM PDT SUN SEP 7 2008/
SHORT TERM (TODAY-WED)...A FEW AFTERNOON CLOUDS DEVELOPING OVER THE
VTU/LA COUNTY MOUNTAINS TODAY BUT SO FAR THEY ARE SHOWING VERY
LITTLE VERTICAL DEVELOPMENT AND I DON`T EXPECT ANY PRECIP FROM THEM.
LITTLE CHANGE TO THE FORECAST THROUGH MIDWEEK. TEMPS FELL A FEW
DEGREES TODAY IN THE LA/VTU COUNTY VALLEYS AND THIS TREND SHOULD
CONTINUE AND BECOME MORE WIDESPREAD AT LEAST THROUGH TUESDAY. 12Z
GFS SHOWS THE TROF DIGGING A LITTLE MORE THAN PREVIOUS RUNS AND WE
COULD ACTUALLY SEE THE COOLING TREND LASTING ANOTHER DAY OR TWO. THE
MARINE LYR, WHICH HAS BEEN CONFINED MOSTLY TO THE COASTAL AND LOWER
COASTAL VALLEY ZONES THE LAST FEW DAYS WILL PUSH FARTHER INLAND EACH
OF THE NEXT FEW DAYS. ALTHOUGH THE FORECAST CURRENTLY DOES NOT HAVE
CLOUDS REACHING THE SOUTHERN SALINAS VALLEY OR THE SANTA CLARITA
VALLEY WOULD NOT BE SURPRISED TO SEE THIS HAPPEN BY TUESDAY MORNING.
LONG TERM (THU-SUN)...WITH THE GFS DIGGING THE TROF FARTHER SOUTH
IT MAY TAKE AN EXTRA DAY OR TWO BEFORE TEMPS START TO REBOUND.
HOWEVER, THE ECMWF HAS A DEEPER LOW BUT ALSO IS FASTER MOVING THE
TROF EAST. THIS SOLUTION WOULD RESULT IN AN EARLIER WARMING TREND.
FOR NOW HAVE TRENDED THE FORECAST CLOSER TO THE COOLER GFS AS THIS
SOLUTION SEEMS A LITTLE MORE PLAUSIBLE.
&&
.AVIATION...08/0003Z.
IFR CONDITIONS WILL LIKELY RETURN TO MOST COASTAL TERMINALS AROUND
02Z...EXCEPT FOR KLGB AND KSBP. KLGB AND KSBP WILL LIKELY SEE IFR
CONDITIONS DEVELOP BETWEEN 04Z AND 08Z TONIGHT...WITH CONFIDENCE
LOWER IN THIS TIMING. THE CENTRAL COASTAL TERMINALS HAVE A 80
PERCENT CHANCE OF LIFR CONDITIONS DEVELOPING BETWEEN 06Z AND 08Z AND
PERSIST INTO AROUND 15Z. SOUTH OF POINT CONCEPTION...THERE IS A 40
PERCENT CHANCE THAT IFR CONDITIONS COULD IMPROVE TO MVFR AFTER 06Z.
IFR CONDITIONS WILL LIKELY DEVELOP AT KBUR AND KVNY AFTER 11Z
TONIGHT.
KLAX...IFR CONDITIONS WILL REDEVELOP OVER THE KLAX AREA BY 02Z...OR
03Z AT THE LATEST. IFR CONDITIONS WILL LIKELY PERSIST WITH A 40
PERCENT CHANCE OF IFR CONDITIONS IMPROVING TO MVFR AFTER 06Z. IF
THERE IS A MOST LIKELY TIME FRAME FOR CEILINGS TO LIFT INTO THE MVFR
CATEGORY...THE CEILING SHOULD LIFT BETWEEN 11Z AND 15Z. VFR
CONDITIONS SHOULD DEVELOP BETWEEN 17Z AND 19Z ON MONDAY.
KBUR...VFR CONDITIONS WILL PERSIST THROUGH AT LEAST 06Z...WITH IFR
CONDITIONS SPREADING INTO THE AREA AFTER 06Z. LOW CONFIDENCE EXISTS
IN THE TIMING OF THE CEILINGS. A MORE LIKELY TIME PERIOD OF 11Z TO
16Z WAS GIVEN...BUT THERE IS A 40 PERCENT CHANCE THAT IFR CEILINGS
COULD DEVELOP BETWEEN 06Z AND 11Z. VFR CONDITIONS WILL REDEVELOP
BETWEEN 15Z AND 17Z ON MONDAY.
&&
.LOX WATCHES/WARNINGS/ADVISORIES...
SMALL CRAFT ADVISORY (SEE LAXMWWLOX).
&&
$$
PUBLIC...HALL/WOFFORD
AVIATION...HALL
WWW.WEATHER.GOV/LOSANGELES
