FXUS66 KLOX 271245 AAA
AFDLOX
SOUTHWEST CALIFORNIA AREA FORECAST DISCUSSION...UPDATED
NATIONAL WEATHER SERVICE LOS ANGELES/OXNARD CA
445 AM PST FRI NOV 27 2009
.SYNOPSIS...A COLD LOW PRESSURE SYSTEM WILL MOVE OVER THE AREA
THROUGH SATURDAY NIGHT...BRINGING COLDER TEMPERATURES...A CHANCE
OF SHOWERS...AND THE POSSIBILITY OF LOW ELEVATION SNOW. AN
OFFSHORE FLOW PATTERN WILL DEVELOP FOR THE EARLY HALF OF NEXT
WEEK WITH A WARMING AND DRYING TREND EXPECTED.
&&
.SHORT TERM (TODAY-SUNDAY)...OFFSHORE FLOW CONTINUES TO WEAKEN
THIS MORNING WITH SURFACE GRADIENTS TRENDING MODERATELY ONSHORE
AHEAD OF A DEVELOPING STORM SYSTEM. LATEST FOG PRODUCT INDICATES
QUITE A BIT OF HIGH LEVEL MOISTURE BEGINNING TO STREAM OVER THE
AREA...WITH EMBEDDED STRATUS BENEATH IT. A FEW SITES ALONG THE
CENTRAL COAST ARE SEEING DENSE FOG THIS MORNING...BUT DENSE FOG
WILL BE PATCHY AS THE MARINE LAYER DEEPENS THROUGHOUT THIS
MORNING.
THE STORM SYSTEM WILL CUT OFF FROM THE UPPER-LEVEL FLOW PATTERN
LATER TODAY. MODEL SOLUTIONS ARE STARTING TO COME INTO AGREEMENT
ON THE TRACK OF THE THE STORMS...TAKING A INTERIOR TRACK. A COLD
FRONT WITH THE SYSTEM ARRIVES LATER TODAY OVER THE NORTHERN
PORTION OF THE AREA TODAY...AND PUSHES SOUTH TO POINT CONCEPTION
THROUGH LATE THIS AFTERNOON. SOME MODEL DIVERGENCE DOES OCCUR
WITH THE FRONTAL BOUNDARY. NAM-WRF SEEMS TO BE HANDLING THE FRONT
A LITTLE MORE AGGRESSIVELY...PUSHING ENOUGH MOISTURE AND THERMAL
SUPPORT THROUGH THE INNER WATERS TO POSSIBLY SUPPORT FOR A BAND
SHOWERS. HOWEVER...THE ECMWF AND GFS SOLUTIONS WEAKEN THE FRONT
AT POINT CONCEPTION. SOME CLARITY WILL LIKELY ARRIVE WITH THE 12Z
SOLUTIONS AS THE FRONTAL BOUNDARY SHOULD BE WITHIN THE NAM-WRF
MODEL DOMAIN. IF THE NAM-WRF SOLUTION PLAYS OUT...IT COULD A BIT
WINDIER THAN WHAT THE GFS AND ECMWF ARE INDICATING...ESPECIALLY
ALONG THE CENTRAL COAST THIS AFTERNOON AND FOR SOUTHERN SANTA
BARBARA COUNTY TONIGHT.
THE BULK OF THE SYSTEMS COLD AIR WILL ARRIVE LATE THIS EVENING OR
AFTER MIDNIGHT...POSSIBLY PRODUCING ISOLATED TO SCATTERED SHOWERS
FOR THE COASTS AND VALLEYS...AND RAIN AND SNOW LIKELY ALONG THE
NORTH-FACING SLOPES OF THE MOUNTAINS. NAM-WRF AND ECMWF
PRECIPITATION AGREE WELL WITH ABOUT 0.20 TO 0.25 HUNDREDTHS OF AN
INCH OF PRECIPITATION OCCURRING OVER THE NORTHERN SLOPES OF THE
MOUNTAINS. WITH THIS EVENT BEING THE FIRST ACCUMULATING SNOW EVENT
OF THE YEAR AND THE BULK OF THE TROPOSPHERE BELOW FREEZING AHEAD
OF THE COLD AIR PUSHING IN...A HIGHER SNOW RATIO COULD OCCUR
POSSIBLY CREATING ADVISORY LEVEL SNOWFALL ACCUMULATION FOR THE
INTERSTATE 5 CORRIDOR AND LOCKWOOD VALLEY. AS A RESULT...A SNOW
ADVISORY HAS BEEN ISSUED FOR THE LOS ANGELES AND VENTURA COUNTY
MOUNTAINS.
THE SYSTEM SHOULD EXIT THE REGION ON SATURDAY NIGHT AND SUNDAY. A
WRAP-AROUND SCENARIO POSSIBLY COULD STILL UNFOLD...BUT MODEL
SOLUTIONS ARE DOWNPLAYING THE SCENARIO. SOME MOISTURE IS STILL
APPARENT OVER THE AREA...THE MAIN PROBLEM SEEMS TO BE WHETHER OR
NOT THE MOISTURE WILL MATERIALIZE. MODELS ARE CONTINUING TO
DEVELOP AN OFFSHORE EVENT FOR SATURDAY NIGHT INTO SUNDAY
MORNING...WITH BREEZY OT WINDY CONDITIONS DEVELOPING OVER THE
AREA. NAM-WRF BUFR TIME HEIGHT SECTION ARE IMPRESSIVE WITH A 50 KT
JET AROUND 7000 FEET...AND WINDS APPROACHING 40 KNOTS AT 850 MB.
EVENT WILL HAVE TO BE MONITORED AS THE SCENARIO UNFOLDS...BUT
ADVISORY LEVEL WINDS LOOKS PROBABLE AT THIS POINT. AS A
RESULT...BREEZY TO WINDY CONDITIONS REMAIN FOR SATURDAY NIGHT AND
SUNDAY FOR PORTIONS OF LOS ANGELES AND VENTURA COUNTIES.
.LONG TERM (MONDAY-THURSDAY)...OFFSHORE FLOW PATTERN SHOULD BEGIN
WEAKENING FOR THE START OF THE WORK WEEK. TEMPERATURES WILL STILL
LIKELY WARM INTO MONDAY AND TUESDAY AS THE RIDGE AXIS MOVES OVER THE
REGION AND THE AIR MASS STAGNATES.
MODELS ARE STRUGGLING WITH A DEVELOPING TROUGH FOR LATE NEXT WEEK.
GFS AND ECMWF ARE IN BROAD DISAGREEMENT IN HOW TO HANDLE THE REMAINS
OF TYPHOON NIDA AND THE UPSTREAM WAVES. WITH MORE EMPHASIS PLACED
ON THE SHORT-TERM AND A LACK OF CONFIDENCE BETWEEN THE MEDIUM-RANGE
SOLUTIONS...FORECAST REMAINS CLOSER TO CLIMATOLOGY.
&&
.AVIATION...27/1200Z.
LIFR CONDS WILL AFFECT KSBP/KSMX THIS MORNING. OTHERWISE...VFR CONDS
EXPECTED ACROSS THE AREA THROUGH THIS AFTERNOON. A FRONT WILL MOVE
ACROSS THE AREA TONIGHT...BRINGING THE THREAT OF LIGHT SHOWERS WITH
MVFR CONDS. COLD AIR ASSOCIATED WITH THE STORM WILL RESULT IN A
SLIGHT CHANCE OF TSTMS FOR THE AREA. GIVEN PERCENTAGE CHANCE
(15-20%) OF TSTMS...WILL NOT MENTION IN 12Z TAFS...AND WILL LET THE
SITUATION BE MONITORED BY THE DAY/SWING SHIFTS.
KLAX...HIGH CONFIDENCE IN 12Z TAF. THERE IS A SLIGHT CHANCE OF TSTMS
LATE THIS EVENING (AFTER 08Z).
KBUR...HIGH CONFIDENCE IN 12Z TAF. THERE IS A SLIGHT CHANCE OF TSTMS
LATE THIS EVENING (AFTER 08Z).
&&
.LOX WATCHES/WARNINGS/ADVISORIES...
HIGH SURF ADVISORY (SEE LAXCFWLOX).
WINTER WEATHER ADVISORY (SEE LAXWSWLOX).
SMALL CRAFT ADVISORY (SEE LAXMWWLOX).
SPECIAL WEATHER STATEMENT (SEE LAXSPSLOX).
&&
$$
SYNOPSIS/PUBLIC...HALL
AVIATION...RAT
WWW.WEATHER.GOV/LOSANGELES
