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FXUS66 KLOX 190424
AFDLOX

SOUTHWEST CALIFORNIA AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LOS ANGELES/OXNARD CA
925 PM PDT THU SEP 18 2008

...UPDATED AVIATION DISCUSSION...

.SHORT TERM (TODAY-SUN)...
THE MENTION OF SLIGHT CHANCE FOR THUNDERSTORMS FOR LA/VTU COUNTY
MTNS AND THE ANTELOPE VALLEY HAS BEEN TAKEN OUT OF THE FORECAST FOR
THIS EVENING AS PEAK DIURNAL HEATING HAS PASSED AND AIRMASS HAS
STARTED TO DRY OUT ACROSS THE AREA AT THE MID LEVELS. NOT EXPECTING
ANY CONVECTION THROUGH THE THE NEXT SEVERAL DAYS.

OVERALL...TEMPS WERE NEAR NORMAL IN MOST LOCATIONS...GIVE OR TAKE A
FEW DEGREES. LATEST AMDAR SOUNDING NEAR KLAX INDICATED A
STRENGTHENING SHALLOW INVERSION NEAR 700 FT DEEP. WHILE MIRAMAR 00Z
SOUNDING WAS NEAR 1500 FT. EXPECT MARINE LAYER TO DEEPEN TO NEAR
1000 FT ACROSS LA COUNTY OVERNIGHT. THIS SHOULD KEEP VALLEYS MOSTLY
CLEAR. LATEST FOG PRODUCT IMAGERY SHOWED A PATCH OF STRATUS ALONG
THE IMMEDIATE COAST NEAR SAN DIEGO. NAM/WRF HAS BEEN HAVING A TOUGH
TIME HANDLING THE RH FIELD IN REGARDS TO THE MARINE LAYER OVER THE
PAST FEW DAYS. SINCE THERE WAS A DECENT AMOUNT OF 850 MB MOISTURE
ACROSS THE COASTAL WATERS OVER THE LAST 24-HOURS...THIS LIKELY
HELPED TO DISRUPT THE MARINE LAYER. CONFIDENCE IF LOW THAT STRATUS
WILL DEVELOP ACROSS LA/VTU COUNTY COASTAL AREAS...BUT A WEAK EDDY
SHOULD DEVELOP OVERNIGHT...SO WILL LEAVE THE MENTION OF PATCHY LOW
CLOUDS ACROSS LA COUNTY AFTER MIDNIGHT...BUT WILL KEEP VTU COUNTY
CLEAR TONIGHT. THERE IS A MODERATE NORTHERLY GRADIENT BETWEEN
SBA-SMX AT -3.6 MB THIS EVENING...THEREFORE SKIES SHOULD REMAIN
CLEAR ACROSS THE SANTA BARBARA SOUTH COAST OVERNIGHT AS WELL. EXPECT
SOME LOCAL NORTHWEST TO NORTH WINDS 15 TO 25 MPH WITH LOCALLY HIGHER
GUSTS BELOW AND THROUGH PASSES AND CANYONS NEAR GAVIOTA AND
MONTECITO THROUGH MIDNIGHT.

FOR FRI...CUT-OFF LOW NEAR THE OR/CA COAST WILL BEGIN TO FILL IN AND
MOVE ACROSS NRN CAL. THE ASSOCIATED WEAK TROF ASSOCIATED WITH THIS
LOW WILL HELP TO LOWER TEMPS A DEGREE OR TWO ACROSS THE FORECAST
AREA...ESPECIALLY AREAS N OF POINT CONCEPTION WHERE SOME INLAND
AREAS COULD LOWER 5 DEGREES. HIGHS SHOULD BE IN THE LOWER TO MID 80S
ACROSS THE INTERIOR VALLEYS OF SLO COUNTY...WHILE THE WARMEST LA/VTU
VALLEY LOCATIONS SHOULD REACH" onClick="return popup(this, 'notes')">REACH 90 WITH MOST AREAS INTO THE MID 80S.
EDDY SHOULD BE BETTER ESTABLISHED BY FRI NIGHT...WHICH SHOULD BRING
IN BETTER AREAL LOW CLOUD COVERAGE FOR LA/VTU COUNTY COASTAL
AREAS...AND POSSIBLY ADJACENT COASTAL VALLEYS. GRADIENTS BETWEEN
SBA-SMX SHOULD STRENGTHEN ONCE AGAIN FRI EVE CREATING GUSTY
NORTHWEST TO NORTHERLY WINDS 20 TO 30 MPH...WITH LOCALLY HIGHER
GUSTS ACROSS THE USUAL WINDY PASSES AND CANYONS ACROSS THE SANTA
YNEZ RANGE. A WIND ADVISORY MIGHT BE NEEDED FOR THE SBA COUNTY MTNS
AND ADJACENT SOUTH COAST. AS THE TROF CONTINUES TO MOVE INLAND...A
BROAD NW FLOW ALOFT WILL PERSIST THROUGH SUNDAY BRINGING NEAR NORMAL
TEMPS TO THE REGION AND LITTLE FLUCTUATION IN TEMPS ACROSS THE
REGION. MOST VALLEY AREAS WILL BE IN THE 80S BOTH DAYS...WHILE THE
COASTAL AREAS REMAIN IN THE HIGHER 60S AND 70S.

...FROM PREVIOUS DISCUSSION...

.LONG TERM (MON-THU)...A TROF MOVING THROUGH THE PAC NW WILL KEEP
DAYTIME TEMPS ABOUT THE SAME MONDAY. BOTH THE ECMWF AND GFS MOVE
THIS TROF RAPIDLY INLAND, BUT FOR SOME REASON THE GFS BUILDS A
STRONG SURFACE HIGH OVER NEVADA AND CREATES A PRETTY STRONG OFFSHORE
FLOW PATTER. GIVEN THE TRAJECTORY OF THE TROF THIS SEEMS WAY
OVERDONE AND I HAVE MORE FAITH IN THE ECMWF WHICH INDICATES
GRADIENTS NEAR NEUTRAL. BOTH MODELS DO SHOW HIGH PRESSURE BUILDING
OVER THE AREA TUE-THU AND CONFIDENCE IS HIGH THAT WE`LL SEE A
SIZABLE WARMING TREND DURING THIS PERIOD.

&&

.AVIATION...19/0345Z.

MAINLY CLEAR SKIES ACROSS THE FORECAST AREA OVERNIGHT...WITH SOME
LOCAL IFR HZ POSSIBLE NEAR KSMX AFTER 10Z. CIGS COULD APPROACH THE
CENTRAL COAST BY 10Z...BUT CONFIDENCE IS LOW FOR THIS.


KLAX...HIGH CONFIDENCE WITH CAVU TAF.

KBUR...HIGH CONFIDENCE WITH CAVU TAF

&&

.LOX WATCHES/WARNINGS/ADVISORIES...
SMALL CRAFT ADVISORY (SEE LAXMWWLOX).

&&

$$

PUBLIC...KAPLAN/WOFFORD
AVIATION...KAPLAN

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