FXUS66 KLOX 261806 AAA
AFDLOX
SOUTHWEST CALIFORNIA AREA FORECAST DISCUSSION...UPDATED
NATIONAL WEATHER SERVICE LOS ANGELES/OXNARD CA
1005 AM PST THU NOV 26 2009
UPDATED AVIATION SECTION ONLY
.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)...OFFSHORE FLOW CONTINUES THIS MORNING,
THOUGH WITHOUT THE UPPER SUPPORT WE'VE HAD THE LAST TWO DAYS SO
WINDS ARE WEAKER AND MORE ISOLATED. HOWEVER, THE WARM AIRMASS
REMAINS IN PLACE SO TODAY WE'LL HAVE TEMPS WELL ABOVE NORMAL BUT
WITHOUT ALL THE WIND SO OVERALL A VERY NICE THANKSGIVING DAY.
GRADIENTS WILL BE TRENDING ONSHORE TONIGHT AND FRIDAY, BUT NOT SOON
ENOUGH TO PERMIT A MARINE LYR TO REDEVELOP SOUTH OF PT CONCEPTION.
NORTH OF THERE HOWEVER LOW CLOUDS MAY REACH THE IMMEDIATE BEACHES
LATER TONIGHT. VISIBLE IMAGERY SHOWS A LARGE BATCH OF LOW CLOUDS
ABOUT 50 MILES WEST OF THE CENTRAL COAST SHORELINE AND THESE SHOULD
BE MOVING CLOSER AS THE DAY GOES ALONG.
MAY STILL BE SOME WEAK OFFSHORE WINDS ACROSS VENTURA AND LA COUNTIES
FRIDAY MORNING BUT GRADIENTS WILL BE TRENDING STRONGLY ONSHORE
THROUGH THE DAY. IN ADDITION, AIRMASS COOLS THROUGH THE DAY SO HIGHS
FRIDAY SHOULD BE ABOUT 10 DEGREES COOLER THAN TODAY.
FORECAST GETS VERY INTERESTING FROM LATE FRIDAY INTO SATURDAY.
UNFORTUNATELY, THE 12Z RUNS MAINTAIN THEIR DIFFERENCES WITH RESPECT
TO THE MOVEMENT OF THE UPPER LOW DOWN THE WEST COAST. THE NAM
CONTINUES TO INDICATE A MORE WESTERLY OVER-WATER TRACK AND WETTER
WHILE THE GFS IS INLAND AND DRIER WITH MORE WIND. WITH THE UPPER LOW
STILL WELL TO THE NORTH OFF THE COAST OF WA IT'S STILL WAY TOO EARLY
TO GIVE EITHER MODEL MORE CREDENCE THAN ANOTHER. AS A RESULT, I PLAN
ON MAKING VERY FEW CHANGES TO THE FORECAST THROUGH SAT, WHICH
ALREADY INDICATES SOME CHANCE OF RAIN ACROSS OUR ENTIRE AREA (EXCEPT
THE DESERTS) LATE FRIDAY AND/OR SATURDAY.
CANNOT RULE OUT THE POSSIBILITY OF SOME CONVECTION WITH THE UPPER
LOW CENTER, MOSTLY EARLY SATURDAY MORNING. NAM SHOWS THE BEST
INSTABILITY WITH THE LOW AND JUST WEST OF THE COLD AIR CORE, WHICH
WOULD KEEP CONVECTIVE CHANCES MOSTLY OVER OUR COASTAL WATERS. THE
GFS IS NOT NEARLY AS UNSTABLE AND IS FURTHER INLAND. WILL PROBABLY
LEAVE OUT THUNDERSTORMS FOR NOW BUT CHANCES ARE NOT ZERO.
WITH THICKNESSES DROPPING TO AROUND 537 EARLY SATURDAY MORNING SNOW
LEVELS SHOULD DROP TO AT OR SLIGHTLY BELOW 4000 FEET, WHICH WOULD
POSE A THREAT FOR SNOW OVER THE GRAPEVINE AND INTERSTATE 5. THIS
WILL BE HAVE TO WATCHED CLOSELY.
OVERALL, STILL A LOT OF UNCERTAINTY WITH THIS EVENT, THOUGH WHAT IS
VIRTUALLY CERTAIN IS THAT SO CAL IS IN FOR A SUBSTANTIAL COOLING
OVER THE NEXT 48 TO 72 HOURS WITH THE POSSIBILITY FOR SOME SHOWERS.
***FROM PREVIOUS DISCUSSION***
.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...26/1800Z.
VFR CONDITIONS EXPECTED AT ALL TAF SITES THRU THE FORECAST PERIOD.
EXPECT IFR/LIFR TO RETURN TO THE IMMEDIATE CENTRAL COAST TONIGHT BUT
SHOULD AVOID KSMX AND KSBP.
KLAX...HIGH CONFIDENCE IN 18Z TAF.
KBUR...HIGH CONFIDENCE IN 18Z TAF.
&&
.LOX WATCHES/WARNINGS/ADVISORIES...
HIGH SURF ADVISORY (SEE LAXCFWLOX).
SMALL CRAFT ADVISORY (SEE LAXMWWLOX).
&&
$$
SYNOPSIS/PUBLIC...WOFFORD/HALL
AVIATION...TRM
WWW.WEATHER.GOV/LOSANGELES
