FXUS66 KLOX 261215
AFDLOX

SOUTHWEST CALIFORNIA AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LOS ANGELES/OXNARD CA
415 AM PST THU NOV 26 2009

.SYNOPSIS...WARM TEMPERATURES AND DRY CONDITIONS WILL PERSIST
THROUGHOUT TODAY AS AN OFFSHORE FLOW PATTERN IN PLACE GRADUALLY
WEAKENS. A COOLING AND MOISTENING TREND WILL OCCUR FOR THE
REMAINDER OF THE LONG WEEKEND AS A WEAK COLD FRONT MOVES OVER THE
AREA ON FRIDAY. AN OFFSHORE FLOW PATTERN WILL DEVELOP EARLY NEXT
WEEK BRINGING DRY AND WINDY CONDITIONS WITH A WARMING TREND.

&&

.SHORT TERM (TODAY-SATURDAY)...GRADIENTS REMAIN MODERATE TO STRONG
OFFSHORE CURRENTLY...BUT AN ONSHORE TREND IS DEVELOPING THIS
MORNING. WITH THE THERMAL SURFACE TROUGH STILL REMAINING OFFSHORE
EARLY THIS MORNING...TEMPERATURES STILL WILL LIKELY REMAIN WARM AT
THE COASTAL AREAS TODAY. HOWEVER...TEMPERATURES SHOULD BE COOLER
ACROSS THE COASTAL AREAS TODAY VERSUS YESTERDAY. AN EARLIER SEA
BREEZE SHOULD PUSH ASHORE EARLIER...USHERING IN A COOLER MARINE
AIR MASS. TEMPERATURES WERE SKEWED IN-LINE WITH MOST VALLEY
LOCATIONS BEING SLIGHTLY WARMER THAN THE COASTS...A REVERSE FROM
THE PAST COUPLE OF DAYS.

AS ONSHORE FLOW ESTABLISHES OVER THE NEXT 24 TO 36 HOURS...DENSE
FOG ISSUES COULD POP UP ESPECIALLY FOR THE CENTRAL COAST
TONIGHT...AND POSSIBLY FOR THE LOS ANGELES COUNTY COASTS. SURFACE
GRADIENTS ARE IN THE PRIME AREA FOR DENSE FOG...BEING SLIGHTLY
OFFSHORE THIS AFTERNOON.

ONSHORE FLOW SHOULD DEVELOP OVERNIGHT TONIGHT FOR THE CENTRAL
COAST...DELAYING UNTIL FRIDAY MORNING FOR THE AREAS SOUTH OF
POINT CONCEPTION. THE DRIVING FORCE WILL BE A WEAK FRONTAL
BOUNDARY PUSHING SOUTH OVER THE REGION. THE FRONTAL BOUNDARY WILL
MOVE OVER THE AREA ON FRIDAY AND FRIDAY NIGHT. PRECIPITATION WILL
BE LIKELY BE SHOWERY WITH THE BOUNDARY MOVING SOUTH...EXCEPT
MAYBE A BAND OF ORGANIZED RAIN NORTH OF POINT CONCEPTION. FLOW
PATTERN DOES NOT SEEMS VERY CONDUCIVE FOR PRODUCING PRECIPITATION
THOUGH. WHILE THE FRONT WILL ACT AS THE LIFTING MECHANISM...THERE
IS VERY LITTLE WARM AIR ADVECTION AHEAD OF THE FRONT. ENOUGH
MOISTURE IS PRESENT IN THE 850 MB MIXING RATIO PATTERN...BUT
MIXING RATIOS ARE NOT AS HEALTHY FOR BANDED PRECIPITATION.
CONSEQUENTLY...THE MODEL SOLUTIONS INDICATE THE LOWER-LEVEL
RELATIVE HUMIDITY BEING ON LOW SIDE AND DISORGANIZED. WITH THE
FRONT STILL IN TACT OVER AREAS NORTH OF POINT CONCEPTION AND
ENOUGH MOISTURE AHEAD ON THE LEADING EDGE OF A JET STREAK...POPS
WERE BUMPED SLIGHTLY FOR FRIDAY AND FRIDAY NIGHT FOR THE CENTRAL
COAST AND ADJACENT INLAND AREAS.

THE BOUNDARY FALLS APART SOUTH OF POINT CONCEPTION ON FRIDAY
NIGHT...WITH A FEW SHOWERS OR SPRINKLES POSSIBLY MAKING IT SOUTH
OF THE POINT. MAIN CONCERN FOR AREAS SOUTH OF POINT CONCEPTION
WILL BE WHEN THE 500 MB COLD POCKET ARRIVES. WITH GOOD AGREEMENT
BETWEEN THE NAM-WRF AND GFS SOLUTIONS...A 500 MB COLD POCKET
PUSHES ALONG THE WESTERN EDGE OF THE SYSTEM...CREATING A MORE
FAVORABLE ENVIRONMENT FOR CONVECTION TO DEVELOP. THE MAJOR HANG UP
SO FAR WITH THE CONVECTIVE SCENARIO PLAYING OUT SEEMS TO BE THE
LACK OF AGREEMENT OF THE OF THE STORMS CIRCULATION. GFS AND GEM
SOLUTIONS MOVE THE CENTER OF THE STORMS THROUGH THE CENTRAL VALLEY
AND INTO THE MOJAVE DESERT...WHICH IS A MORE LIKELY SCENARIO FOR
THIS TIME OF YEAR. HOWEVER...THE NAM-WRF IS MUCH WETTER SOLUTION
DIGGING THE STORM CENTER ALONG THE CALIFORNIA COAST. THIS WILL PUT
THE COLD POCKET OVER THE COASTAL WATERS...A POSSIBLY BRINGING A
BETTER CHANCE TO PICKUP SOME PACIFIC MOISTURE FEED INTO THE STORM
SYSTEM. WITH HIGHER CONFIDENCE IN THE GEM AND GFS SOLUTIONS...POPS
REMAINS ON THE LOW-SIDE...BUT ENOUGH COLD AIR COULD PUSH INTO THE
AREA TO GENERATE ISOLATED SHOWERS FOR SATURDAY.

A VERY LIKELY OCCURRENCE WITH THIS SYSTEM WILL BE A STRONG
NORTHERLY GRADIENT DEVELOPING FRIDAY NIGHT AND INTO SATURDAY
NIGHT. THIS GRADIENT WILL LIKELY AFFECT SOUTHERN SANTA BARBARA
COUNTY AND THE INTERSTATE 5 CORRIDOR....WITH WINDY CONDITIONS
THROUGH AND BELOW PASSES AND CANYONS. ADVISORY OR WARNINGS MAY
NEEDED IN THE FUTURE FOR THIS SYSTEM DEPENDING ON HOW THE TRACK
EVOLVES AND FLOW PATTERN DEVELOPS. IF A WINTRY MIX OF
PRECIPITATION IS THROWN INTO THE MIX...A TREACHEROUS COMMUTE
THROUGH THE INTERSTATE COULD BE POSSIBLE FOR INTERSTATE 5
CORRIDOR ON SATURDAY AND SATURDAY NIGHT.

.LONG TERM (SUNDAY-WEDNESDAY)...AS THE STORM EXISTS THE
REGION...MODELS ARE IN REASONABLE AGREEMENT FOR SOME WRAP-AROUND
UPSLOPE PRECIPITATION DEVELOPING FOR THE DESERT AND THE NORTHEAST
AND EAST FACING SLOPES OF THE MOUNTAINS. ALL MEDIUM RANGE
SOLUTIONS SEEM TO INDICATE THE POSSIBILITY...BUT THE TIMING OF
ITS ACTUAL OCCURRENCE STILL PRESENTS A PROBLEM. CONFIDENCE IS
GROWING IN AN UPSLOPE PRECIPITATION EVENT...WITH SNOW LEVELS
POSSIBLY DOWN TO THE FOOTHILL LEVEL OF THE ANTELOPE VALLEY.
HOWEVER...MODELS ARE HAVING TROUBLE WITH THE EXACT TIME PERIOD OF
DEVELOPING PRECIPITATION. WITH MUCH LEEWAY TO HAMMER DOWN THE
TIMING...POPS WERE BUMPED FOR SATURDAY NIGHT AND SUNDAY...BUT
PRECIPITATION COULD OCCUR AS EARLY AS LATE SATURDAY NIGHT...OR AS
LATE AS EARLY MONDAY MORNING.

A STRONG SURFACE HIGH WILL BUILD INTO THE GREAT BASIN ON SUNDAY
NIGHT ALLOWING A MODERATE TO STRONG SANTA EVENT TO SET UP. THE
PATTERN WILL REMAIN PERSISTENT INTO MIDWEEK BEFORE WEAKENING. THIS
EVENT WILL BE A COOLER SANTA ANA EVENT AS A COOL AIR MASS WILL
REMAIN IN PLACE BEHIND THE EXITING STORM SYSTEM. WHILE
TEMPERATURES WILL WARM IN THE OFFSHORE FLOW PATTERN...TEMPERATURES
WILL NOT BE AS WARM AS THEY WERE THE LAST COUPLE OF DAYS. THIS
EVENT WILL HAVE TO BE MONITORED CLOSELY AS THE SCENARIO PROGRESSES
AS A STRONG 500 MB JET ACCOMPANIES THE OFFSHORE PUSH...ALONG THE
WITH DECENT AMOUNTS OF THERMAL PACKING BETWEEN THE DESERT AND THE
COASTAL PLAIN.

&&

.AVIATION...26/1200Z.

VFR CONDITIONS EXPECTED AT ALL TAF SITES THRU THIS EVENING. SOME
GUSTY OFFSHORE WINDS EXPECTED OVER VENTURA AND LOS ANGELES COUNTY 
AIRFIELDS THROUGH EARLY THIS AFTERNOON...WITH LOW LEVEL WIND SHEAR 
POSSIBLE AT KBUR AND KVNY. EXPECT IFR/LIFR TO RETURN TO THE CENTRAL
COAST TONIGHT...POSSIBLY AFFECTING KSMX AND KSBP. 

KLAX...HIGH CONFIDENCE IN 12Z TAF

KBUR...HIGH CONFIDENCE IN 12Z TAF.

&&

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

&&

$$

SYNOPSIS/PUBLIC...HALL
AVIATION...SIRARD/RAT

WWW.WEATHER.GOV/LOSANGELES