FXUS66 KLOX 252347 AAA
AFDLOX

SOUTHWEST CALIFORNIA AREA FORECAST DISCUSSION...UPDATE
NATIONAL WEATHER SERVICE LOS ANGELES/OXNARD CA
345 PM PST FRI DEC 25 2009

UPDATE FOR NEW AVIATION DISCUSSION

.SYNOPSIS... 
A WEAK UPPER LEVEL RIDGE WILL CONTINUE TO KEEP CONDITIONS DRY ACROSS 
THE AREA THROUGH SATURDAY EVENING. A SERIES OF WEAK STORM SYSTEMS 
MOVING THROUGH THE EASTERN PACIFIC WILL BRING A SLIGHT CHANCE OF 
RAIN TO PARTS OF THE REGION SATURDAY NIGHT THROUGH MONDAY...THEN DRY 
AND SEASONABLY COOL WEATHER IS EXPECTED TUESDAY THROUGH THURSDAY.

&&

.SHORT TERM (TONIGHT-MON)...BIGGEST IMMEDIATE CONCERN THIS AFTERNOON 
IS WHETHER MARINE LAYER CLOUDS WILL RETURN TO COASTAL AREAS TONIGHT. 
VERY LIMITED AMOUNT LAST NIGHT IN THE SANTA MONICA BAY. LATEST LAX 
OBSERVATION AND COASTAL WEBCAMS CONFIRM THE EXISTENCE OF MARINE 
LAYER CLOUDS IN THE BIGHT NOW, A PRECURSOR TO WHAT WILL HAPPEN AFTER 
DARK. WILL MENTION IN FORECASTS FOR JUST THE COASTAL ZONES SOUTH OF 
SBA WITH ONLY ISOLATED ALONG THE CENTRAL COAST LIKE SMX. GRADIENTS 
ARE STILL WEAKLY OFFSHORE AND WHILE I ANTICIPATE THEM GOING ONSHORE 
TONIGHT, DEPTH SHOULD REMAIN BELOW 1500 FEET AND WILL KEEP OUT OF 
ALL VALLEYS.     

UPPER LEVEL RIDGE OF HIGH PRESSURE NOW ALIGNED JUST OFF THE WEST 
COAST APPROXIMATELY ALONG 124W. FIRST UPSTREAM SYSTEM, BASED UPON 
SAT PIXS, EXTENDS SOUTH FROM 50N TO NEAR 35N AND THEN SW TO NEAR HI. 
IMPRESSIVE ASSOCIATED MOISTURE FIELD WITH 12Z GFS 6 HR PW VERIFYING 
NEARLY SPOT ON WITH 1.40 INCHES! MODELS WEAKEN AND SHIFT UPPER RIDGE 
OFF TO THE EAST OVER THE NEXT 24 HOURS. THIS ALLOWS THE FIRST 
UPSTREAM SYSTEM TO PUSH TOWARD THE COAST BUT SUBSEQUENT STRETCHING 
AND ELONGATING WEAKENS THE SYSTEM TO NEARLY NOTHING BY THE TIME IT 
REACHES THE COAST. 18Z WRF BRINGS MEASURABLE RAIN TO THE CENTRAL 
COAST NOW ABOUT 6 HOURS LATER - ABOUT 00Z/27 - BUT KEEPS CONDITIONS 
DRY OVER THE ENTIRE CWA IN SUBSEQUENT PERIODS. 18Z GFS IS ONLY 
MARGINALLY MORE ROBUST WITH LESS THAN A TENTH OF AN INCH QPF AND ALL 
OF IT LIMITED TO NORTH OF PT. CONCEPTION. WILL MAINTAIN POPS OVER 
NORTHERN HALF OF CWA BUT REMOVE FROM THE SOUTH. 

MODELS ALL AGREE ON SOLUTION FOR SECOND SYSTEM WHICH NOW ROTATES 
SOUTH AND WEST OF SOUTHERN CA SUN NIGHT/MON. HAVE TRIMMED OR 
ELIMINATED POPS IN ZONES FOR SUN NIGHT/MON AND FUTURE SHIFTS MAY 
NEED TO REMOVE POPS ALTOGETHER AND BRIGHTEN UP THE CLOUD FORECAST AS 
WELL. WOULD NOT BE ALL THAT SURPRISED IF FUTURE MODEL GUIDANCE 
SUPPORTS A COMPLETELY DRY MONDAY WITH PLENTY OF SUNSHINE AND MILD 
OFFSHORE FLOW.  

.LONG TERM (TUE-FRI)...A NWLY FLOW PATTERN ALOFT WILL SET UP OVER 
THE FCST AREA TUE THRU THU...WITH DRY WEATHER EXPECTED...AND TEMPS 
SLIGHTLY BELOW NORMAL. A WEAK TROF PASSES THROUGH NORTHERN CA ON WED 
BUT EFFECTS ON OUR AREA WILL LIKELY JUST BE CLOUDS. PRESENTLY A NICE 
BROAD UPPER RIDGE IS FORECAST FOR NEW YEARS DAY LEADING TO PLENTY OF 
SUNSHINE AND AT OR SLIGHTLY ABOVE NORMAL TEMPS TO START THE NEW 
YEAR.  

&&

.AVIATION...25/2340Z...THERE IS A 30 PERCENT CHANCE KSMX...AND A 20 
PERCENT CHANCE KLAX AND KLGB MAY NOT HAVE LOW CLOUDS AND MVFR 
CONDITIONS LATE TONIGHT AND SAT MORNING. OTHERWISE...THERE IS  
GENERALLY HI CONFIDENCE IN THE CURRENT TAF PACKAGE.

KLAX...THERE IS A 20 PERCENT CHANCE LOW CLOUDS AND MVFR CONDITIONS 
MAY NOT AFFECT THE AIRFIELD LATE TONIGHT INTO SAT MORNING... 
OTHERWISE GENERALLY HI CONFIDENCE IN THE CURRENT TAF.

KBUR...HI CONFIDENCE IN THE CURRENT TAF. 

&&

.LOX WATCHES/WARNINGS/ADVISORIES...
NONE

&&

$$

PUBLIC...TRM
AVIATION...SIRARD
SYNOPSIS...TRM

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