000
FXUS66 KLOX 200539
AFDLOX
SOUTHWEST CALIFORNIA AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LOS ANGELES/OXNARD CA
939 PM PST WED NOV 19 2008
.UPDATE...HIGH LEVEL MOISTURE MOVING OVER THE AREA WILL MAKE FOR A
DIFFICULT MARINE LAYER FORECAST TONIGHT. DENSE FOG ISSUES COULD
LIKELY BE KEPT TO A MINIMUM TONIGHT...BUT WITH MARINE INVERSION SO
THIN AND SURFACE GRADIENTS SO WEAK...PATCHY DENSE FOG SEEMS TO
MAKE SENSE WITH THE CURRENT PACKAGE. FOR THE CURRENT TIME...IT IS
LIKELY THAT DENSE FOG ADVISORIES MAY NOT BE NEEDED TONIGHT.
HOWEVER...MARINE LAYER IS STILL EXPECTED TO BE AN ISSUE
TONIGHT...BUT IT WILL REMAIN DIFFICULT TO FORECAST AS HIGH LEVEL
MOISTURE WILL LIKELY OBSCURE THE PATCHES OF STRATUS. IT IS
POSSIBLE THAT SOME VALLEY AREAS COULD SEE THE MARINE LAYER CREEP
IN LATE...ESPECIALLY THE SANTA YNEZ AND SAN GABRIEL VALLEYS.
KSBA-KSMX GRADIENTS HAVE SURGED TO 4.1 MB OUT OF THE NORTH...AND
SOME SITES ARE GUSTING INTO THE 30S WITH LAS FLORES CANYON
SUSTAINED WINDS AROUND 30 MPH. AN ADVISORY HAS BEEN ISSUED FOR
SOUTHERN SANTA BARBARA COUNTY. THE END TIMING OF THE ADVISORY WAS
A CONCERN AS NAM-WRF SURFACE GRADIENTS ARE UNDERDONE TONIGHT...AND
ARE NOT VERY RELIABLE. CLIMATOLOGY WOULD SUGGEST AN ENDING TIME
AROUND MIDNIGHT...HOWEVER...WITH NAM-WRF INDICATING THE STRONGEST
THERMAL GRADIENTS AT 09Z...AND ANOTHER MAXIMA AT 15Z. THE ADVISORY
WAS EXTENDED UNTIL 8 AM...OR 16Z. BOUNDARY LAYER WINDS ALSO PEAK
AT 09Z AS WELL.
A DRY BOUNDARY PUSHING SOUTH DOWN THE STATE CURRENTLY WILL ARRIVE
OVER THE AREA ON THURSDAY AFTERNOON. WITH 10 DEGREE THERMAL
GRADIENTS DEVELOPING BETWEEN THE SAN JOAQUIN VALLEY AND THE SANTA
BARBARA CHANNEL...AND THE COLDEST AIR PUSHING INTO THE NORTHEAST
SLOPES OF THE SANTA BARBARA COUNTY MOUNTAINS...IT IS LIKELY THE
FOCUS OF THE ADVISORY LEVEL EVENT WILL BE PLACED ON SANTA BARBARA
COUNTY THURSDAY NIGHT AND FRIDAY. SOME BREEZY CONDITIONS WILL
LIKELY OCCUR IN THE I-5 CORRIDOR...BUT ADVISORY LEVEL WINDS WILL
PROBABLY NOT DEVELOP THROUGH I-5 CORRIDOR. IT IS LIKELY THAT SOME
ADVISORY LEVEL GUSTS WILL OCCUR ON WHITAKER PEAK THOUGH. SOME
CONCERN BASED ON THERMAL PATTERN THAT THE SANTA YNEZ VALLEY MAY BE
AFFECTED...AND WINDS WILL LIKELY HAVE TO BE BUMPED UP FOR THIS
AREA.
&&
.PREV DISCUSSION... /ISSUED 200 PM PST WED NOV 19 2008/
SHORT TERM (TODAY-SATURDAY)...
TEMPS DOWN ACROSS THE BOARD TODAY...AS RIDGE CONTINUES TO MOVE TO
THE EAST AND GRADS SLOWLY TREND ONSHORE. THE BIGGEST COOLING HAS
BEEN REALIZED ALONG THE COAST THANKS TO A GREATER MARINE LAYER
PRESENCE. TEMPS ALONG THE COAST ARE TRENDING 6-15 DEGREES COOLER
THAN YESTERDAY. ELSEWHERE...TEMPS ARE DOWN ON THE ORDER OF 2-6
DEGREES. ALTHOUGH IT DID BREAK UP NICELY TODAY...EXPECTING AN EVEN
GREATER STRATUS COVERAGE TONIGHT INTO TOMORROW AS ONSHORE GRADS
INCREASE. DENSE FOG WILL BE A CONCERN AGAIN AND ADVISORIES MAY BE
REQUIRED AGAIN. INLAND AREAS SHOULD SEE THE MOST SIGNIFICANT DROP IN
TEMPS ON THU THANKS TO THE LESSENING INFLUENCE OF THE RIDGE TO THE
EAST AND GREATER ONSHORE/MARINE FLOW.
A WEAK AND DRY FRONT STILL LOOKS TO PASS OVER THE AREA THU/THU
NIGHT...WHICH WHEN COUPLED WITH A BUILDING SURFACE HIGH BEHIND
IT...WILL BRING SIGNIFICANT NORTHERLY WINDS. LAX-BFL GRAD LOOKS TO
PEAK AT A HEALTHY -7.0 MB LATE THU NIGHT. AN ADVISORY LEVEL
SUNDOWNER OVER SBA COUNTY REMAINS IN THE CARDS AS A RESULT...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
CONTINUE TO ADDRESS THAT. THIS TIGHT GRADIENT WILL ALSO PRODUCE
GUSTY NORTHERLY FLOW OVER THE MTNS OF LA/VTU COUNTY...ESPECIALLY THE
I-5 CORRIDOR...WHICH MAY REQUIRE AN ADVISORY.
THIS FLOW WILL SHIFT NORTHEASTERLY LATE FRI MORNING. THIS WIND
SHOULD CLEAR OUT ANY STRATUS AND ALLOW TEMPS TO WARM UP A BIT...BUT
NOT TOO MUCH AS GENERAL TROUGHINESS IS EXPECTED AT THE UPPER LEVELS.
THE CENTRAL COAST WILL LIKELY SEE THE BIGGEST TEMP BOOST AND SOME
LOCAL BREEZIES. THE ONE LAST WRINKLE IS THAT THERE IS SOME MOISTURE
EMBEDDED IN THIS FLOW...WHICH MAY CAUSE SOME CLOUDS/FOG TO FORM ON
THE NORTH FACING SLOPES AND THE FAR INTERIOR PORTIONS OF SBA/SLO
COUNTIES. ALTHOUGH SOME LOCALLY BREEZY NORTHEAST CONDITIONS WILL
CONTINUE INTO SAT OVER LA/VTU COUNTY...IT WILL GENERALLY NOT BE MORE
THAN THE 15 TO 25 MPH VARIETY. THIS WILL HELP TO KEEP THINGS ABOVE
NORMAL TEMP-WISE...AND KEEP THINGS MOSTLY CLEAR...OTHER THAN SOME
LINGERING CIRRUS.
LONG TERM (SUNDAY-WEDNESDAY)...
GENERALLY LIGHT OFFSHORE FLOW IS EXPECTED THROUGH MON...AS A SERIES
OF WEAK-MODERATE SURFACE HIGHS FORM OVER IDAHO AND UTAH. THE MODELS
CONTINUE TO STRUGGLE WITH THE TIMING OF THE STRENGTH OF THE SURFACE
HIGH...BUT THEY ARE ALL NOW SAYING THAT THIS WILL NOT BE MUCH OF A
WIND EVENT. WITH THE TROUGH ALOFT AS WELL...NOT ONLY WILL UPPER
LEVEL SUPPORT BE IN THE WRONG DIRECTION...BUT TEMPS WILL NOT NEARLY
BE AS WARM AS WHAT OCCURRED THIS LAST WEEKEND. GENERALLY 70S TEMPS
WILL BE THE COMMON PLACE.
TUE AND WED STILL CONTINUES TO BE TOUGH TO NAIL DOWN...BUT BOTH THE
ECMWF AND THE GFS SHOW AN AMPLIFIED TROUGH MOVING OVER THE PACIFIC
WHICH COULD PRODUCE SOME PRECIP OVER CA. WE WILL CONTINUE TO WATCH
THIS WITH EAGER ANTICIPATION...BUT WITH THE LARGE SPREAD IN THE
ENSEMBLES AND THE MODELS BOUNCING ALL OVER THE PLACE RUN-TO-RUN...AT
THIS POINT CANNOT IN GOOD CONSCIENCE GO WITH MORE THAN 10 POPS AND
PARTLY CLOUDIES FOR THE MIDDLE OF NEXT WEEK.
&&
.AVIATION...20/0009Z.
VFR CONDITIONS ARE EXPECTED TO PERSIST AT ALL INLAND TERMINALS
EXCEPT KPRB. THERE IS A SLIGHT CHANCE OF MVFR CONDITIONS DEVELOPING
BETWEEN 11Z AND 16Z AT KBUR AND KVNY. AT COASTAL TERMINALS AND
KPRB...SOME CONCERN EXISTS THAT INCREASING HIGH LEVEL MOISTURE MAY
LIMIT LIFR TO IFR CONDITIONS TONIGHT. IT IS POSSIBLE THAT ONLY MVFR
CONDITIONS MAY DEVELOP. TIMING OF LIFR TO IFR CONDITIONS SHOULD
OCCUR AFTER 09Z...BUT WITH LOWER CONFIDENCE OF IFR CONDITIONS
DEVELOPING. PACKAGE MAY BE UPDATED LATER TO IMPROVE CONDITIONS.
KLAX...VFR CONDITIONS SHOULD OCCUR THROUGH AT LEAST 04Z...WITH IFR
TO MVFR CONDITIONS DEVELOPING AFTER 04Z...OR AS LATE AS 09Z. LOW
CONFIDENCE EXISTS WITH LIFR CONDITIONS DEVELOPING AROUND 11Z AS HIGH
LEVEL MOISTURE COULD KEEP CONDITIONS IN THE MVFR RANGE THROUGHOUT
TONIGHT AND INTO THURSDAY AFTERNOON.
KBUR...VFR CONDITIONS ARE EXPECTED THROUGHOUT THE PERIOD EXCEPT FOR
A 20 PERCENT CHANCE OF MVFR CONDITIONS DEVELOPING BETWEEN 11Z AND
16Z.
&&
.LOX WATCHES/WARNINGS/ADVISORIES...
WIND ADVISORY (SEE LAXNPWLOX).
FIRE WEATHER WATCH (SEE LAXRFWLOX).
SMALL CRAFT ADVISORY (SEE LAXMWWLOX).
GALE WARNING (SEE LAXMWWLOX).
&&
$$
HALL/KITTELL
WWW.WEATHER.GOV/LOSANGELES
