000
FXUS66 KLOX 190546
AFDLOX

SOUTHWEST CALIFORNIA AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LOS ANGELES/OXNARD CA
946 PM PST TUE NOV 18 2008

.UPDATE...SURFACE GRADIENTS ARE ALL TRENDING ONSHORE THIS
EVENING...EXCEPT KSBA-KSMX SURFACE GRADIENTS...AS SOUTHWEST FLOW
ALOFT ESTABLISHES OVER THE AREA. MARINE LAYER CLOUDS AND FOG HAVE
PUSHED INTO THE CENTRAL COAST THIS EVENING...AND WITH KSMX-KBFL
AND KSMX-KLAS GRADIENTS ALL WEAKLY ONSHORE THIS EVENING...SOME
CONCERN EXISTS FOR DENSE FOG FORMATION LATER THIS EVENING NORTH
OF POINT CONCEPTION. LATER THIS EVENING DENSE FOG ISSUES MAY
OCCUR OVER THE AREA SOUTH OF POINT CONCEPTION WHEN GRADIENTS ARE
EXPECTED TO BE NEAR NEUTRAL. CENTRAL COAST OBSERVATIONS ARE
STARTING TO INDICATE SOME SIGNS OF GOING DENSE...AND UPDATES WILL
LIKELY FOLLOW.

A TROUGH OF LOW PRESSURE OVER THE EASTERN PACIFIC WILL STRENGTHEN
THE ONSHORE FLOW TREND ON WEDNESDAY AND WEDNESDAY NIGHT. BETTER
COOLING AND A BIT MORE MOISTURE WILL PUSH INTO THE INLAND AREAS.
WITH AN ONSHORE FLOW PATTERN IN PLACE...LOW CLOUDS AND FOG WILL
LIKELY PUSH INTO THE VALLEY AREAS WEDNESDAY NIGHT INTO THURSDAY
MORNING. NAM-BUFR DATA INDICATES MARINE LAYER INVERSIONS
INCREASING TO NEAR 1100 FEET AT KLAX AND KLGB BY THURSDAY
MORNING. THIS SHOULD PUSH SOME MARINE LAYER STRATUS CLOUDS INTO
THE SAN GABRIEL VALLEY AND COULD PUSH LOW CLOUDS AND FOG INTO THE
LOWER ELEVATIONS OF THE SAN FERNANDO VALLEY.

A WEAK BOUNDARY DROPS SOUTH OVER THE AREA THURSDAY AFTERNOON AND
THURSDAY NIGHT...AND ARRIVES ALONG THE NORTHERN SLOPES LATE
THURSDAY MORNING. THERMAL PACKING AND SURFACE GRADIENTS BECOME
MODERATE TO STRONG BETWEEN THE SAN JOAQUIN VALLEY...YET BOUNDARY
LAYER AND 850 MB WINDS INDICATE HARDLY ANY FLOW AT ALL. NAM-WRF
850 MB THERMAL GRADIENTS APPROACH 10 DEGREES CELSIUS...AND KLAX-
KBFL AND KSBA-KBFL SURFACE GRADIENTS ARE -6.8 MB AND -6.4 MB
RESPECTIVELY BY 12Z FRIDAY. HOWEVER...850 MB AND BOUNDARY LAYER
WINDS ARE ALL 10 TO 15 KNOTS OVER THE AREA. GFS INDICATES SIMILAR
TRENDS WITH THERMAL GRADIENTS BEING STRONGER RELATIVE TO WINDS
AT 850 MB. WITH LITTLE UPPER-LEVEL SUPPORT...IT IS PROBABLY BEST
AT THIS POINT TO TREND TOWARDS ADVISORY LEVEL WINDS DEVELOPING
FOR THURSDAY NIGHT AND FRIDAY FOR SOUTHERN SANTA BARBARA COUNTY
AND THROUGH I-5 CORRIDOR.

THE FLOW PATTERN TURNS NORTHEAST OVER THE WEEKEND...SETTING UP
ANOTHER SANTA ANA PATTERN. NAM-WRF IS LOOKING SLIGHTLY STRONGER
THAN THE GFS BUT THERE CONTINUES TO BE GREAT UNCERTAINTY WITH THE
PATTERN. THE GFS ENSEMBLE SOLUTIONS ARE STARTING TO TREND TOWARDS
A WEAKER DIRECTION AWAY FROM THE STRONGER NAM-WRF SOLUTION. IT IS
CERTAIN THAT THERE WILL BE OFFSHORE FLOW PATTERN THIS
WEEKEND...BUT ITS TIMING AND STRENGTH IS UNCERTAIN AT THIS POINT.

&&

.PREV DISCUSSION... /ISSUED 200 PM PST TUE NOV 18 2008/

SHORT TERM (TODAY-FRIDAY)...
THE UPPER LEVEL RIDGE CONTINUES TO SLOWLY MOVE EASTWARD...AS IT
CURRENTLY SITS OVER ARIZONA. OFFSHORE GRADS REMAIN IN PLACE BUT ARE
WEAKENING AS WELL. TODAY ENDED UP WARM AS A RESULT...BUT SLIGHTLY
COOLER THAN YESTERDAY. THE GREATEST COOLING WAS ALONG THE COASTAL
SECTION AS THE MARINE LAYER BEGINS TO RE-ASSERT ITSELF. THE CENTRAL
COAST REALLY TOOK A HIT...DOWN AS MUCH AS 15 DEGREES FROM YESTERDAY
AS A PERSISTENT STRATUS LAYER SITS ALONG THE COAST. WINDS ARE ON THE
LIGHT SIDE AND HUMIDITIES HAVE COME UP SOME...WHICH HAVE CERTAINLY
HELPED THE FIREFIGHTING EFFORTS.

TODAY WAS THE START OF A TREND THAT WILL BE AMPLIFIED TONIGHT INTO
WED. EXPECTING GRADS TO CONTINUE TO TURN ONSHORE...AND THE MARINE
LAYER TO SPREAD OVER A LARGER AREA. LOW CLOUDS AND DENSE FOG NOW
SEEMS LIKELY ALONG ALL COASTAL SITES BY DAYBREAK. AS THE RIDGE
FLATTENS AND THE COOL MARINE INFLUENCE SPREADS OUT...THE BIGGEST
DROP IN TEMPS SHOULD OCCUR TOMORROW. MINS SHOULD COOL A NUMBER OF
DEGREES WHILE MOST COASTAL AND VALLEY SITES WILL SEE MAX TEMPS DOWN
ABOUT 6-12 DEGREES. WINDS WILL REMAIN LIGHT...BUT WITH MORE
AFTERNOON SEABREEZE COVERAGE. THU WILL BE EVEN COOLER THAN WED AS
THESE ONSHORE TRENDS CONTINUE AND SOME POSSIBLY THICK CIRRUS CLOUDS
MOVE OVERHEAD.

A WEAK AND DRY FRONT WILL PASS OVER THE AREA ON THU/THU
NIGHT...WHICH WHEN COUPLED WITH A BUILDING SURFACE HIGH BEHIND
IT...WILL BRING SIGNIFICANT NORTHERLY WINDS. EXPECTING AN ADVISORY
LEVEL SUNDOWNER TO SBA COUNTY...WHICH WILL BE MORE OF A
NORTH-NORTHEASTERLY VARIETY AND SHOULD UNFORTUNATELY IMPACT THE
MONTECITO AREA. THESE WINDS WILL NOT BE NEARLY AS STRONG AS WHAT
OCCURRED THIS LAST WEEKEND...BUT WILL CREATE HEIGHTENED FIRE WEATHER
CONCERNS...AND A FIRE WX WATCH WILL BE ISSUED TODAY TO ADDRESS THAT.
IN ADDITION...THIS NORTHERLY FLOW WILL LIKELY AFFECT THE MTNS OF
LA/VTU COUNTY...ESPECIALLY THE I-5 CORRIDOR.

ALTHOUGH THERE IS A CHANCE THAT SOME STRATUS MAY LINGER NEAR LA
CO...THIS NORTHERLY FLOW SHOULD SCOUR OUT ANY STRATUS BY FRI. IN
FACT...IT LOOKS LIKE THERE WILL BE SOME DECENT NORTHEAST FLOW ALONG
THE CENTRAL COAST...WHICH WILL NOT ONLY CLEAR THINGS OUT...BUT
SHOULD ALSO WARM THINGS UP QUITE A BIT. THE REST OF THE AREA SHOULD
SEE A SMALL BUMP UP IN TEMPS AS WELL.

LONG TERM (SATURDAY-TUESDAY)...
THE NORTHERLY FLOW PREVIOUSLY MENTIONED WILL SHIFT TO NORTHEASTERLY
FRI NIGHT. THERE IS BETTER AGREEMENT TODAY AS FAR AS THE OVERALL
PICTURE FOR THIS WEEKEND...NAMELY OFFSHORE FLOW SAT AND SUN. BOTH
MODELS AGREE IN INTENSITY...AS BOTH BUILD A 1036MB SURFACE HIGH INTO
THE GREAT BASIN...BUT THE MAIN DIFFERENCE REMAINS IN THE PEAK
TIMING. THE GFS SHOWS A PEAK FRI NIGHT INTO SAT...WHILE THE ECMWF
CONTINUED TO SHOW SAT NIGHT/SUN AS THE PEAK. EITHER WAY...WE ARE IN
STORE FOR SOME MORE OFFSHORE FLOW AND ASSOCIATED DRYING/WARMING.
LIKE THE THU NIGHT NORTHERLY EVENT...THIS OFFSHORE EVENT WILL NOT BE
AS STRONG AS THIS PAST WEEKEND. THE KEY DIFFERENCE IS THAT BOTH
MODELS ACTUALLY SHOW TROUGHING ALOFT. THIS WILL NOT ONLY INHIBIT
UPPER LEVEL SUPPORT AND ANY DUCTING EFFECTS...BUT IT WILL ALSO KEEP
THINGS COOLER THAN THESE PAST FEW DAYS.

MON AND TUE STILL REMAINS UNCERTAIN...BUT THE GFS AND ECMWF ARE
COMING A BIT MORE IN LINE THAN THEY WERE YESTERDAY. AS OF NOW...IT
LOOKS LIKE A FAIRLY COLD LOW WILL DROP DOWN OVER THE ERN PAC FROM
ALASKA ON MON...WHICH WOULD QUICKLY WEAKEN ANY OFFSHORE FLOW. THIS
LOW LOOKS TO BRING A CHANCE OF PRECIPITATION TO THE REGION SOMETIME
EARLY TO MIDDLE NEXT WEEK. CANNOT NAIL DOWN ANY MORE THAN THAT AT
THIS POINT DUE TO THE ALWAYS PRESENT TIMING AND MOISTURE SOURCE
CONCERNS...BUT IT WILL CERTAINLY BE SOMETHING WE WILL ANXIOUSLY BE
KEEPING AN EYE ON.

&&

.AVIATION...19/0002Z.
VFR CONDITIONS ARE EXPECTED TO PERSIST AT ALL INLAND TERMINALS
EXCEPT FOR A SLIGHT CHANCE OF IFR TO MVFR CONDITIONS AT KPRB BETWEEN
12Z AND 16Z. AT COASTAL TERMINALS NORTH OF POINT CONCEPTION...LIFR
TO IFR CONDITIONS WILL SPREAD OVER KSMX AND KSBP AFTER 0230Z...OR AS
LATE AS 05Z. AT COASTAL TERMINALS SOUTH OF POINT CONCEPTION...LOW
CONFIDENCE EXISTS IN CURRENT PACKAGE...ESPECIALLY WITH KLAX AND
KLGB. FORECAST NUDGES DIRECTION OF MVFR CONDITIONS DEVELOPING OVER
THE AREA AFTER 09Z. AT KOXR AND KSBA...AN EARLIER RETURN WITH BETTER
COVERAGE IS EXPECTED AFTER 04Z TONIGHT...BUT IT COULD BE AS EARLY AS
02Z...OR AS LATE 08Z.

KLAX...VFR CONDITIONS ARE EXPECTED THROUGH AT LEAST 06Z...OR AS LATE
AS 09Z. LOW CONFIDENCE EXISTS IN THE CURRENT PACKAGE AFTER 06Z.
AFTER 06Z...MVFR VISIBILITIES WILL LIKELY DEVELOP WITH A 60 PERCENT
CHANCE OF LIFR CONDITIONS DEVELOPING BETWEEN 09Z AND 14Z. VFR
CONDITIONS COULD DEVELOP AS SOON AS 15Z...OR AS LATE AS 19Z.

KBUR...VFR CONDITIONS ARE EXPECTED THROUGHOUT THE PERIOD WITH NO
WIND ISSUES.

&&

.LOX WATCHES/WARNINGS/ADVISORIES...
FIRE WEATHER WATCH (SEE LAXRFWLOX).
MARINE WEATHER STATEMENT (SEE LAXMWSLOX).

&&

$$

HALL/KITTELL

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