High Surf Advisory 19, NWS Los Angeles, CA

SOUTHWEST CALIFORNIA AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LOS ANGELES/OXNARD CA
1003 AM PST WED NOV 23 2011

...UPDATED AVIATION DISCUSSION...

.SYNOPSIS...

WEAKENING HIGH PRESSURE ALOFT WILL ALLOW A TROUGH TO MOVE OVER
THE REGION ON THANKSGIVING DAY. COOLER TEMPERATURES ARE EXPECTED
WITH POSSIBLE PRECIPITATION. A HIGH PRESSURE RIDGE WILL BUILD
OVER THE AREA BEHIND THE TROUGH ON FRIDAY WITH OFFSHORE WINDS AND
A SIGNIFICANT WARMING TREND THROUGH THE WEEKEND. TEMPERATURES
ABOVE SEASONAL NORMALS ARE POSSIBLE THROUGH EARLY NEXT WEEK.

&&

.UPDATE...

HIGH LEVEL MOISTURE WILL CONTINUE TO THICKEN TODAY AHEAD OF TROUGH
OVER THE EASTERN PACIFIC. THE LATEST INFRARED IMAGERY SUGGESTS A
DENSE DECK OF HIGH LEVEL CLOUDINESS WILL MOVE OVER THE AREA
TONIGHT. CLOUD COVER WILL BE REEVALUATED AND LIKELY INCREASED FOR
TONIGHT.

MAIN PROBLEM OF THE DAY SEEMS TO BE THE MOVEMENT OF THE TROUGH
THROUGH FRIDAY. MODEL COMPARISONS OF GOES WINDS AT 850 MB...500
MB...AND 250 MB SUGGEST THAT THE UKMET AND ECMWF SOLUTIONS SEEMS
TO BE HANDLING THE FINER DETAILS OF THE TROUGH BETTER THAN THE
NAM-WRF AND GFS SOLUTIONS. BOTH SOLUTIONS SUGGEST A DRIER
SOLUTION FOR THE THANKSGIVING HOLIDAY...WHILE GFS SOLUTIONS ARE
THE OUTLIER IN OFFERING UP A WETTER SOLUTION...ESPECIALLY NORTH OF
POINT CONCEPTION. THE BEST CHANCE OF ANY PRECIPITATION SHOULD BE
FOR AREAS NORTH OF POINT CONCEPTION. UNFORTUNATELY...BETTER
CLARIFICATION ON THE SYSTEM MAY NOT OCCUR UNTIL THE SYSTEM CUTS
OFF FROM THE FLOW ON THANKSGIVING MORNING AND MODEL SOLUTIONS
GET THE CHANCE TO CATCH UP. AT THE VEARY LEAST...A CLOUDY AND
COOL DAY SHOULD BE EXPECTED FOR THANKSGIVING. FOR THE CURRENT
TIME...SATELLITE DATA WILL MONITORED CLOSELY FOR CLARITY ON THE
SCENARIO.

&&

.PREV DISCUSSION...

SHORT TERM...THE FOCUS THEN TURNS TO A PESKY SYSTEM MOVING
THROUGH THE ERN PACIFIC WHICH HAS NOT BEEN HANDLED PARTICULARLY
WELL BY THE MODELS. A TROUGH AND ITS ASSOCIATED SURFACE FRONT WILL
APPROACH THE WEST COAST TONIGHT. LOTS OF ENERGY WILL DROP STRAIGHT
SWD...ALLOWING A CLOSED UPPER LOW TO FORM WELL TO WEST OF POINT
CONCEPTION LATE TONIGHT OR EARLY THU...WHILE THE NORTHERN STREAM
TROUGH WEAKENS. THE UPPER LOW WILL TRACK INTO NORTHERN BAJA BY THU
EVENING. TWO SUBTLE BUT POTENTIALLY IMPORTANT CHANGES ARE WORTH
NOTING ON THE LATEST MODELS. FIRST...THE ECMWF AND ESPECIALLY 06Z
GFS HOLD THE NORTHERN STREAM FRONTAL SYSTEM TOGETHER SOMEWHAT
BETTER THAN ON PREVIOUS RUNS. THE GFS BRINGS BETWEEN ONE QUARTER
AND ONE HALF INCH OF RAIN TO WESTERN SLO AND SBA COUNTIES VERY
LATE TONIGHT AND THU MORNING...WITH MUCH LESS RAIN OVER EASTERN
PORTIONS OF THOSE COUNTIES. HATE TO WAFFLE ON THIS...BUT HAVE
BUMPED UP POPS A BIT ON THE CENTRAL COAST. SECOND...WHILE THE GFS
STILL KEEPS MOST OF THE RAIN WEST OF VTU AND L.A. COUNTIES...IT
JUST BARELY MISSES...AND THE TREND IS NOW A BIT CLOSER TO THE
COAST. WILL LEAVE IN THE SLIGHT CHANCE POPS FOR THU FOR L.A. AND
VTU COUNTIES. EVEN IF THE MAIN BAND OF RAIN STAYS W OF L.A. AND
VTU COUNTIES...THERE COULD BE SOME WARM FRONTAL UPSLOPE LIGHT RAIN
ON THU.

ANY THREAT OF RAIN SHOULD BE GONE THU EVENING AS THE UPPER LOW CONTS
TO MOVE S. NWLY FLOW PATTERN WILL SET UP ACROSS THE REGION ON FRI AS
AN UPPER RIDGE AMPLIFIES OFF THE COAST. THERE WILL BE PLENTY OF
SUNSHINE ON FRI AND TEMPS WILL BE UP SEVERAL DEGREES IN MOST
AREAS...THOUGH STILL SLIGHTLY BELOW NORMAL.

LONG TERM...THE UPPER HIGH WILL CONT TO AMPLIFY AND SHIFT EWD FRI
NIGHT AND SAT. AT THE SAME TIME...STRONG SFC HIGH PRESSURE WILL
DROP SWD INTO THE ROCKY MTNS. THIS WILL SET UP A DECENT OFFSHORE
FLOW PATTERN...WHICH WILL RESULT IN GUSTY NE WINDS ACROSS THE MTNS
AND VLYS OF L.A. AND VTU COUNTIES...THE VTU COUNTY COASTAL
PLAIN...AND POSSIBLY THE MTNS OF SLO COUNTY. TEMPS WILL JUMP UP
SIGNIFICANTLY W OF THE MTNS ON SAT...WITH THE WARMEST LOCATIONS
ACROSS INTERIOR SECTIONS OF THE COASTAL PLAIN AND POSSIBLY THE
VLYS PROBABLY HAVING MAX TEMPS NEAR OR JUST ABOVE 80 DEGREES.
GUSTY WINDS WILL LIKELY CONTINUE INTO SUNDAY...THEN OFFSHORE GRADS
WILL GRADUALLY RELAX. THE UPPER RIDGE WILL HOLD STRONGLY THRU AT
LEAST MON...AND POSSIBLY TUE...ALTHOUGH THE 06Z RUN OF THE GFS
SHOWS AN INSIDE SLIDER CAUSING THE RIDGE TO BREAK DOWN. THE 00Z
RUN SHOWED NOTHING LIKE THIS AND NEITHER DOES THE ECMWF.
THEREFORE...EXPECT WELL ABOVE NORMAL TEMPS TO CONT MON AND TUE.

&&

.AVIATION...23/1800Z

NORTH OF POINT CONCEPTION...THERE IS A 30 PERCENT CHANCE THAT LIFR
CIGS WILL PERSIST THROUGH 20Z TODAY...OTHERWISE HI CONFIDENCE IN
TAFS THROUGH AROUND 08Z THU. AFTER THAT TIME THERE IS A 40 PERCENT
CHANCE OF LIGHT RAIN AFFECTING THE TAF SITES.

SOUTH OF POINT CONCEPTION...HI CONFIDENCE IN CURRENT TAFS. THERE IS
A 30 PERCENT CHANCE OF LIGHT RAIN AFTER 12Z THU.

KLAX...HI CONFIDENCE IN THE CURRENT TAF WITH VFR CONDITIONS EXPECTED
THROUGH 12Z THU. THERE IS A 30 PERCENT CHANCE OF MVFR CIGS AFTER 12Z
AND A 20 PERCENT CHANCE OF LIGHT RAIN THROUGH 24Z THU.

KBUR...HI CONFIDENCE IN THE CURRENT TAF WITH VFR CONDITIONS EXPECTED
THROUGH 18Z THURSDAY.

&&

.LOX WATCHES/WARNINGS/ADVISORIES...
NONE.

&&

PUBLIC...HALL/BRUNO
AVIATION...ASR/SMITH
SYNOPSIS...SETO/HALL

WWW.WEATHER.GOV/LOSANGELES

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