856 
FXUS66 KLOX 170432
AFDLOX

SOUTHWEST CALIFORNIA AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LOS ANGELES/OXNARD CA
832 PM PST WED NOV 16 2011

.SYNOPSIS...

WEAK OFFSHORE FLOW WILL KEEP THURSDAY DRY AND WARM. A STORM WILL
MOVE SOUTH INTO THE AREA ON FRIDAY. THE STORM SYSTEM WILL MAINLY
BRING CLOUDS AND COOLER WEATHER THROUGH THE WEEKEND...EXCEPT FOR A
SLIGHT CHANCE OF RAIN AND MOUNTAIN SNOW BETWEEN FRIDAY AND
SATURDAY. ANOTHER STORM SYSTEM WILL BRING A BETTER CHANCE OF RAIN
TO THE AREA ON SUNDAY.

&&

.UPDATE...

A HIGH PRESSURE RIDGE OVER THE REGION IS FLATTENING THIS
EVENING...EVIDENT BY THE LATEST WATER VAPOR IMAGERY. AN UPSTREAM
COLD FRONT MOVING INTO THE PACIFIC NORTHWEST THIS EVENING WILL
MOVE SOUTH OVER THE AREA BETWEEN EARLY FRIDAY MORNING AND FRIDAY
NIGHT. THE MAIN INFLUENCE OF THE FRONT WILL BE TO BRING A COOL AND
MORE CLOUDY PATTERN TO THE AREA. THE BEST CHANCE OF ANY
PRECIPITATION WILL OCCUR FOR AREAS NORTH OF POINT CONCEPTION AND
ALONG THE NORTHERN SLOPES OF THE MOUNTAINS. WITH NAM-WRF 850 MB
MIXING RATIOS NEAR BETWEEN 4 AND 6 G/KG AS THE FRONT MOVES SOUTH
INTO SAN LUIS OBISPO COUNTY...ENOUGH MOISTURE IS PRESENT TO
POSSIBLY PRODUCE SOME SHOWERS. NAM BUFR TIME HEIGHT SECTIONS DO
LOOK RATHER WEAK FOR MOISTURE...BUT STILL ENOUGH MOISTURE IS
PRESENT WITH THE DEPTH OF MOISTURE AT KSBP UP TO 6000 FEET DEEP.
FOR NOW...SLIGHT CHANCE POPS LOOK AGREEABLE AND NO CHANGES ARE
PLANNED.

AHEAD OF THE STORM SYSTEM ON THURSDAY...HIGH LEVEL MOISTURE WILL
INCREASE. GFS 300MB AND 400 MB RELATIVE HUMIDITY VALUES INDICATE
PERIODS OF BROKEN HIGH LEVEL CLOUDINESS STREAMING OVER THE AREA.
NEAR THE COAST...THE MARINE LAYER WILL LIKELY PERSIST ESPECIALLY
SOUTH OF POINT CONCEPTION. OFFSHORE GRADIENTS IN PLACE HAVE
THINNED THE MARINE LAYER TO BETWEEN 700 TO 1000 FEET THIS EVENING.
SOME CONCERN EXISTS FOR SOME PATCHY CLOUDS DEVELOPING FOR THE
SANTA BARBARA COASTAL AREAS AND THIS WILL BE ADDED TO THE PACKAGE
THROUGH THURSDAY MORNING. WITH THE DEPTH OF THE MARINE LAYER BEING
THIN...PATCHES OF DENSE FOG ARE POSSIBLE EARLY THURSDAY MORNING.

&&

.PREV DISCUSSION...

SHORT TERM...THIS FIRST STORM SYSTEM IS EXPECTED TO TAKE TOO
MUCH OF AN INLAND TRACK TO GENERATE MUCH IN THE WAY OF PRECIP,
HOWEVER AREAS NORTH OF PT CONCEPTION COULD SEE A SHOWER OR TWO
FRIDAY AND FRIDAY NIGHT. FURTHER SOUTH, STRONG ONSHORE FLOW
PUSHING THE LOW LVL MOISTURE UP AGAINST THE FOOTHILLS ALONG WITH
SUBSTANTIAL COOLING ALOFT COULD GENERATE SOME LIGHT SHOWERS FRIDAY
NIGHT INTO EARLY SATURDAY. IN ALL CASES AMOUNTS ARE EXPECTED TO BE
LIGHT, GENERALLY A TENTH OF AN INCH OR LESS.

SATURDAY IS NOW EXPECTED TO BE A DRY DAY FOR MOST AREAS. COULD SEE 
SOME LINGERING EARLY MORNING PRECIP FOR ERN LA COUNTY VALLEYS/MTNS 
AS WELL AS THE GRAPEVINE AREA AS NORTHWEST FLOW INCREASES. IN FACT, 
WITH SNOW LEVELS FALLING RAPIDLY FRIDAY NIGHT THERE COULD BE SOME 
LIGHT SNOWFALL OVER THE GRAPEVINE THROUGH EARLY SATURDAY MORNING. 
SHOULD SEE MORE SUNSHINE BY SATURDAY AFTERNOON, THOUGH A COOL 
NORTHWEST FLOW WILL KEEP TEMPERATURES MAINLY IN THE 50S TO LOWER 60S 
AT LOWER ELEVATIONS UNDER PARTLY CLOUDY SKIES.

LONG TERM...A MUCH TOUGHER FORECAST FOR SUNDAY AS A SECOND STORM
SYSTEM DROPS SOUTH ALONG THE WEST COAST. THERE HAVE BEEN FAIRLY
LARGE RUN TO RUN CHANGES AND MODEL AGREEMENT AT THIS POINT IS POOR
ENOUGH THAT WE ARE STILL IN A SITUATION WHERE THERE IS A RATHER
LARGE RANGE OF POSSIBILITIES. THE CANADIAN AND UK SOLUTIONS
CONTINUE TO KEEP THE UPPER LOW CLOSER TO THE COAST, KEEPING SO CAL
IN A WETTER SCENARIO. HOWEVER, THE ECMWF AND NOW THE GFS ARE
TAKING IT FURTHER OFFSHORE. WHILE THE DIFFERENCE BETWEEN THE
FARTHEST WEST AND FARTHEST EAST SOLUTIONS MAY ONLY BE A COUPLE
HUNDRED MILES OR SO, THIS IS EASILY ENOUGH TO BE THE DIFFERENCE
BETWEEN A RAINY DAY AND A DRY ONE. BOTH THE EC AND CANADIAN HAVE
BEEN VERY CONSISTENT RUN TO RUN, WHILE THE GFS HAS ONLY RECENTLY
BEEN TRENDING WEST AND DRIER. NONE OF THE MODELS ARE SHOWING ANY
SIGNIFICANT SOUTHERLY FLOW OR MOISTURE TAP SO THAT'S DIFFERENT
FROM THE SYSTEM LAST WEEKEND. PWATS WITH THIS SYSTEM TOP OUT
AROUND .8" WHICH IS A GOOD QUARTER INCH LESS THAN LAST WEEKEND. MY
INSTINCT IS TO FOLLOW THE DRIER EC/GFS SOLUTIONS, BUT NOT ENOUGH
TO MAKE ANY DRAMATIC CHANGES TO POPS AT THIS TIME, ESPECIALLY
GIVEN WHAT HAPPENED LAST WEEKEND. I DID LOWER THEM SLIGHTLY FOR
SUNDAY, ESPECIALLY SOUTHERN AND EASTERN AREAS. THE UPPER RANGE FOR
RAINFALL AMOUNTS WITH THIS SYSTEM WOULD BE A HALF TO ONE INCH, BUT
REALISTICALLY IT'S LOOKING CLOSER TO A TENTH TO A HALF. SNOW
LEVELS ARE PRETTY LOW, GENERALLY 4000 TO 5000 FEET SUNDAY.

THE ECMWF IS A LITTLE SLOWER MOVING THE SYSTEM OUT, BUT MOST AREAS 
SHOULD SEE A DRYING TREND SUNDAY NIGHT INTO EARLY MONDAY. LIGHT 
OFFSHORE FLOW AND SUNSHINE SHOULD YIELD A GOOD 5-10 DEGREES OF 
WARMING MONDAY. THEN CONTINUED RIDGING OVER THE AREA TUESDAY SHOULD 
BRING ANOTHER FEW DEGREES OF WARMING.

THE NEXT SYSTEM WILL START TO APPROACH THE AREA WEDNESDAY. THERE IS 
A SMALL CHANCE OF PRECIP NORTHERN AREAS WEDNESDAY AFTERNOON BUT A 
BETTER CHANCE ON THANKSGIVING DAY.

&&

.AVIATION...16/2347Z.

NORTH OF POINT CONCEPTION...VFR CONDITIONS WILL PERSIST THROUGHOUT 
THE PERIOD EXCEPT FOR A CHANCE OF VLIFR TO LIFR CONDITIONS AT KPRB 
BETWEEN 10Z AND 17Z THURSDAY.

SOUTH OF POINT CONCEPTION...THERE IS A CHANCE OF IFR TO MVFR 
CONDITIONS DEVELOPING BETWEEN 06Z TONIGHT AND 13Z THURSDAY...AND 
PERSISTING INTO BETWEEN 16Z AND 18Z THURSDAY. HIGHEST CONFIDENCE 
EXISTS FOR THE COASTAL TERMINALS.

KLAX...VFR CONDITIONS SHOULD PERSIST THROUGH AT LEAST 06Z 
TONIGHT...WITH IFR TO MVFR CONDITIONS DEVELOPING BETWEEN 06Z AND 10Z 
TONIGHT. HIGHEST CONFIDENCE IN IFR TO MVFR CONDITIONS IS PLACED 
BETWEEN 11Z AND 14Z THURSDAY. THERE IS A 30 PERCENT CHANCE THAT KLAX 
COULD REMAIN VFR THROUGHOUT THE PERIOD.

KBUR...VFR CONDITIONS ARE EXPECTED THROUGHOUT THE PERIOD...EXCEPT 
FOR A 20 PERCENT CHANCE OF IFR TO MVFR CONDITIONS BETWEEN 11Z AND 
15Z THURSDAY.  

&&

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

&&

$$

PUBLIC...HALL/WOFFORD
AVIATION...HALL
SYNOPSIS...B/HALL

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