291 
FXUS66 KLOX 201610
AFDLOX

SOUTHWEST CALIFORNIA AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LOS ANGELES/OXNARD CA
910 AM PDT SAT OCT 20 2012

.SYNOPSIS...
A DEEPENING MARINE LAYER WILL BRING LOW CLOUDS...FOG...AND DRIZZLE 
OR LIGHT RAIN AND COOLER TEMPERATURES THROUGH MONDAY. A LOW PRESSURE 
SYSTEM WILL BRING A CHANCE OF RAIN TO THE AREA MONDAY AND TUESDAY. 
HIGH PRESSURE IS EXPECTED TO BRING DRY AND WARMER CONDITIONS BY THE 
END OF THE WEEK.
 
&&

.SHORT TERM (TODAY-MON)...
THE UPPER LEVEL LOW THAT IS THE REMNANTS OF HURRICANE PAUL HAS 
FINALLY OPENED UP INTO A TROUGH AND WILL SWING THROUGH SOUTHERN 
CALIFORNIA TODAY AND TONIGHT. THIS HAS ALLOWED THE MARINE LAYER TO 
DEEPEN QUICKLY TO AROUND 3500 FEET THIS MORNING...WHICH HAS RESULTED 
IN STRATUS PUSHING DEEP INTO THE VALLEYS AND COASTAL SLOPES. THIS 
HAS ALSO BROUGHT FAIRLY WIDESPREAD DRIZZLE TO THE AREA...THAT IS 
RESULTING IN A FEW AREAS PICKING UP MEASURABLE ACCUMULATIONS. WITH 
ONSHORE GRADIENTS EXPECTED TO RUN AROUND 4 MB STRONGER ONSHORE THAN 
24 HOURS AGO...THERE IS A GOOD CHANCE THAT CLEARING WILL BE SLOW AND 
PATCHY AT BEST THIS AFTERNOON. THE INVERSION IS FAIRLY WEAK 
HOWEVER...SO THIS SCENARIO IS FAR FROM LOCKED IN...BUT A MOSTLY 
GLOOMY AND COOL AFTERNOON IS THE MOST LIKELY OUTCOME. GUSTY ONSHORE 
WINDS ARE ALSO EXPECTED OVER THE INTERIOR AREAS WITH THE STRONG 
ONSHORE TRENDS...ESPECIALLY IN THE ANTELOPE VALLEY. MADE A MINOR 
UPDATE TO THE FORECAST TO ADD 20 POPS TO MOST COASTAL AND VALLEY 
AREAS THIS MORNING...AND UPPED CLOUDS A BIT IN THE AFTERNOON WITH A 
LITTLE MORE COOLING TO TEMPERATURES AS A RESULT.

***FROM PREVIOUS DISCUSSION***

BY TONIGHT...THE CUTOFF LOW THAT HAS BEEN SPINNING OFF THE COAST OF 
BAJA THE PAST SEVERAL DAYS WILL FINALLY GET EATEN UP BY THE BROAD 
UPPER LEVEL TROUGH DEEPENING OVER SOUTHERN CALIFORNIA. AS H5 HEIGHTS 
AND THICKNESS LVLS LOWER WITH THIS DEEPENING TROUGH...THE MARINE 
LAYER WILL DEEPEN EVEN FURTHER...TO AROUND 4500 FT BY TONIGHT INTO 
SUNDAY MORNING. LATEST NAM12 CROSS SECTION SHOWS SOME ADDITIONAL 
LIFT WITH THIS DEEP MARINE LAYER. AT THE LEAST THERE WILL BE AREAS 
OF DRIZZLE ACROSS LOS ANGELES AND VENTURA COUNTIES TO THE COASTAL 
SLOPES. 20 PERCENT POPS LOOKS GOOD AS THERE SHOULD BE SOME 
MEASURABLE RAIN INTO SUNDAY MORNING...ESPECIALLY AROUND THE 
FOOTHILLS WHERE THE ADDITIONAL TOPOGRAPHY LIFT SHOULD ACT LIKE A 
SPONGE AND ENHANCE  RAINFALL AMOUNTS TO OVER A TENTH OF AN 
INCH...ESPECIALLY ALONG THE SAN GABRIEL MOUNTAIN FOOTHILLS LIKE A 
CANADA/FLINTRIDGE AND LA CRESCENTA AREAS. 

SKIES ONCE AGAIN WILL HAVE A TOUGH TIME CLEARING OUT ACROSS THE 
COASTAL PLAIN WITH ONLY PARTIAL CLEARING EXPECTED FOR THE VALLEYS 
SOUTH OF POINT CONCEPTION. A COOLING TREND WILL CONTINUE INTO SUNDAY 
WITH MOST AREAS AWAY FROM THE MOUNTAINS ONLY REACHING THE UPPER 60S 
TO LOWER 70S. TEMPS WILL BE COOLER THAN NORMAL FOR THIS TIME OF 
YEAR. BY MONDAY...A COLD 532 DM UPPER LOW SITUATED OFF THE COAST OF 
WASHINGTON WITH A VERY DEEP TROUGH EXTENDING ACROSS ALL OF 
CALIFORNIA WILL SWING A FEW EMBEDDED SHORTWAVES ACROSS THE NORTHERN 
PORTION OF THE FORECAST AREA ON MONDAY. THE NAM-WRF...GFS AND ECMWF 
ARE IN GOOD AGREEMENT BRINGING IN A COLD FRONT INTO THE SLO AND SBA 
COUNTIES ON MONDAY...THEN AS THE FRONT HOLDS TOGETHER MOVE INTO 
VENTURA AND LOS ANGELES COUNTIES LATE MONDAY NIGHT INTO TUESDAY.

AT THIS TIME...BEST GUEST FOR PRECIP ESTIMATES WILL BE BETWEEN A 
TENTH TO A THIRD OF AN INCH FOR AREAS N OF POINT CONCEPTION. WHILE 
RAINFALL TOTALS SOUTH OF POINT CONCEPTION WILL BE LESS AS THE FRONT 
WEAKENS OVER VENTURA AND LA COUNTIES. SNOW LEVELS WILL ALSO REMAIN 
ABOVE RESORT LEVELS TO AROUND 7500 FT MONDAY...THEN LOWERING TO 
AROUND 6500 FT BY TUESDAY. THERE COULD BE A QUICK DUSTING OF SNOW AT 
HIGH RESORT LEVELS BY TUESDAY. BUT WITH LIMITED MOISTURE TO WORK 
WITH...DONT GET TOO EXCITED.   


.LONG TERM (TUE-FRI)...BOTH GFS AND ECMWF ARE IN FAIRLY GOOD 
AGREEMENT THROUGH THE EXTENDED PERIOD...EXCEPT THE GFS ADVERTISES 
A RIDGE BUILDING OFF THE CALIFORNIA COAST WELL INTO THE GULF OF 
ALASKA WHILE THE ECMWF CONTINUES A ZONAL TO WEAK TROUGH OVER THE 
WEST. 

EARLIER MODEL RUNS WERE SLOWER WITH THE ARRIVAL AND EXIT OF 
THE RAINY PERIOD THROUGH THE FORECAST AREA. BOTH MODELS HAVE BACKED 
OFF SOME WITH THE PROGRESSION OF A SECONDARY SHOT OF MOISTURE 
TUESDAY NIGHT INTO WED. HOWEVER...THE UPPER TROUGH WILL CONTINUE TO 
REMAIN OVERHEAD KEEPING TEMPS QUITE COOL AND CONTINUED LOW LEVEL 
MOISTURE TO BRING A FEW PERIODS OF SHOWERS AFTER THE MAIN RAIN 
THREAT ON MONDAY TO EARLY TUESDAY MORNING. BY WEDNESDAY 
AFTERNOON...EXPECT CLEAR TO PARTLY CLOUDY SKIES ACROSS MUCH OF THE 
FORECAST AREA. WEDNESDAY WILL BEGIN A MILD WARMING TREND INTO 
THURSDAY BEFORE OFFSHORE FLOW DEVELOPS WARMING UP COAST AND COASTAL 
VALLEYS LATE NEXT WEEK. WARMEST TEMPS SHOULD REACH THE MID 80S BY 
FRI...WITH ADDITIONAL WARMING BY NEXT WEEKEND. 

&&

.AVIATION...20/1130Z...
DEEP MARINE LAYER AND GOOD ONSHORE FLOW HAS ENTRENCHED STRATUS 
ACROSS ALL COASTAL/VALLEY TAF SITES...WITH GENERALLY MVFR CONDS 
SOUTH OF POINT CONCEPTION...AND LIFR/IFR CONDS NORTH OF POINT 
CONCEPTION. CLEARING THIS AFTERNOON WILL BE SLOW AND SHORT-LIVED AS 
STRATUS WILL FILL IN QUICKLY THIS EVENING.

KLAX...MODERATE CONFIDENCE IN 12Z TAF. THERE IS A 40% CHANCE THAT 
CIGS WILL REMAIN THROUGH THE AFTERNOON.

KBUR...MODERATE CONFIDENCE IN 12Z TAF. THERE IS A 40% CHANCE THAT
CIGS WILL REMAIN THROUGH THE AFTERNOON. 

&&

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

&&

$$

PUBLIC...KITTELL/KAPLAN
AVIATION...RAT
SYNOPSIS...CK

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