FXUS66 KLOX 262144
AFDLOX
SOUTHWEST CALIFORNIA AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LOS ANGELES/OXNARD CA
145 PM PST THU NOV 26 2009
.SYNOPSIS...
WARM TEMPERATURES AND LIGHT OFFSHORE WINDS WILL CONTINUE THROUGH
TODAY. FRIDAY WILL BEGIN THE TRANSITION TO A COOLING TREND AS
LOW PRESSURE BRINGS ONSHORE FLOW THROUGH SATURDAY ALONG WITH A
CHANCE OF SHOWERS. SUNDAY IS EXPECTED TO BRING ANOTHER ROUND OF
OFFSHORE WINDS WITH MODERATE WARMING LASTING INTO MID WEEK.
&&
.SHORT TERM (TODAY-SUN)...ONE LAST DAY OF WARM OFFSHORE FLOW TODAY
WITH LOWER ELEVATION HIGHS IN THE 80S AND GENERALLY LIGHTER AND MORE
ISOLATED NORTHEAST WINDS. ALTHOUGH GRADIENTS WILL STILL BE OFFSHORE
FRIDAY MORNING, THE AMOUNT WILL BE ABOUT HALF OF TODAY AND GRADIENTS
WILL BE TRENDING STRONGLY ONSHORE THROUGH THE DAY. THIS IS REFLECTED
REALLY WELL IN THE 950 MB TEMP/WIND PATTERN FOR TOMORROW WHICH SHOWS
TEMPERATURES ACTUALLY FALLING THROUGH THE DAY AS WINDS SHIFT TO
ONSHORE. AS A RESULT, HIGHS FRIDAY WILL BE ABOUT 10-15 DEGREES
COOLER THAN TODAY. WENT AHEAD AND KEPT IN THE LOW CLOUDS FOR THE
CENTRAL COAST TONIGHT AS SAT IMAGERY SHOWS THEM NOT TOO FAR OFFSHORE
AND ONSHORE TRENDS SHOULD HELP THEM ADVANCE TOWARDS THE COAST
OVERNIGHT. PROBABLY STILL TOO MUCH OFFSHORE FLOW FRIDAY MORNING
THOUGH TO ALLOW CLOUDS TO DEVELOP SOUTH OF PT CONCEPTION.
THE UPPER LOW THAT IS CURRENTLY CENTERED JUST OFFSHORE OF THE WA
COAST WILL START TO DROP SOUTH TONIGHT AND FRIDAY. THE TRAJECTORY OF
THIS LOW AS IT MOVES SOUTH OVER THE NEXT 36 TO 48 HOURS WILL BE
CRITICAL IN DETERMINING THE IMPACTS FOR OUR AREA. ALTHOUGH THE MODEL
DISAGREEMENTS ARE MINOR IN TERMS OF DISTANCE, EVEN MINOR
DISCREPANCIES CAN LEAD TO MAJOR CHANGES IN THE WEATHER. HENCE THE
RATHER UNCERTAIN AND WISHY-WASHY FORECAST. THE 18Z NAM WAS SOMEWHAT
ENCOURAGING IN THAT IT ACTUALLY RESEMBLED THE PATH SHOWN BY THE GFS
AND ECMWF, THAT IS A MORE INSIDE PATH. SO AT LEAST NOW WE'RE SEEING
SOMEWHAT BETTER AGREEMENT BETWEEN THE MODELS. THE INSIDE PATH WOULD
BE A WINDIER BUT DRIER SCENARIO, WITH THE BEST CHANCES FOR PRECIP
ALONG THE NORTH FACING MOUNTAIN SLOPES AND INTERIOR SLO COUNTY. OUR
FORECASTS HAVE BEEN TRENDING THIS DIRECTION ALREADY SO I DIDN'T NEED
TO MAKE MAJOR ADJUSTMENTS. HOWEVER, THIS PATH WILL RESULT IN THE
COLD AIR CORE MOVING RIGHT OVERHEAD AS THE LOW TRACKS SOUTH. WHEN
THIS HAPPENS, A SHOWER COULD DEVELOP JUST ABOUT ANYWHERE SO SLIGHT
CHANCE POPS LOOK GOOD FOR EVEN LA/VENTURA COUNTY COAST AND VALLEYS.
AND CAN'T RULE OUT SOME CONVECTION WITH THE LOW CENTER, THOUGH
THUNDERSTORMS ARE NOT CURRENTLY PART OF THE OFFICIAL FORECAST.
WITH THE COLD CORE OVERHEAD SAT MORNING SNOW LEVELS WILL DROP QUITE
LOW, POSSIBLY TO BETWEEN 3500 AND 4000 FEET. IMPACTS ACROSS THE
GRAPEVINE AND INTERSTATE 5 COULD BE SIGNIFICANT SATURDAY MORNING IF
ENOUGH UPSLOPE FLOW DEVELOPS TO HELP ENHANCE THE PRECIP THERE.
SHOWER CHANCES SHOULD BE ENDING SATURDAY AFTERNOON MOST AREAS EXCEPT
THE MOUNTAINS. PROBABLY ANOTHER 5-10 DEGREE DROP IN HIGHS SAT, AND
POSSIBLY AS MUCH AS 20-25 DEGREES COOLER IN THE MOUNTAINS.
NORTH/NORTHEAST FLOW WILL DEVELOP BEHIND THE TROF PASSAGE LATE
SATURDAY INTO SUNDAY. THE 18Z NAM IS STILL SHOWING A PRETTY SIZABLE
AMOUNT OF WRAP AROUND MOISTURE EARLY SUNDAY MORNING. THE COMBINATION
OF THE MOISTURE AND GOOD UPSLOPE FLOW COULD GENERATE SOME DECENT
PRECIP ACROSS THE NORTH FACING LA COUNTY MOUNTAINS AND POSSIBLY
VENTURA COUNTY AND THE ANTELOPE VALLEY AS WELL. ALTHOUGH THE COLDEST
AIR WILL HAVE SHIFTED SOUTH BY THAT TIME, ENOUGH COLD AIR SHOULD
REMAIN TO KEEP SNOW LEVELS AROUND 4000 FT, WITH POTENTIALLY
SIGNIFICANT SNOW IN THE LOCAL MOUNTAINS. WILL HAVE TO KEEP A CLOSE
EYE ON THIS OVER THE NEXT FEW MODEL RUNS TO SEE IF THE NAM CONTINUES
TO INDICATE THIS PATTERN DEVELOPING. THE GFS WAS QUITE A BIT DRIER
BUT STILL HAD DECENT NORTHEAST FLOW.
ELSEWHERE, THE NORTHEAST WINDS SHOULD KEEP IT DRY AND GENERALLY
CLEAR SOUTH AND WEST OF THE MOUNTAINS. DESPITE THE OFFSHORE FLOW
DEVELOPING, TEMPS WILL REMAIN QUITE COOL WITH HIGHS MOSTLY IN THE
60S ON SUNDAY AND BREEZY IN MANY AREAS.
.LONG TERM (MON-THU)...WARMING TREND TO CONTINUE MONDAY AND TUESDAY
UNDER WEAK TO MODERATE OFFSHORE FLOW. AIRMASS DOESN'T WARM UP QUITE
AS MUCH AS IT HAS WITH THE CURRENT OFFSHORE EVENT SO HIGHS SHOULD
TOP OUT MOSTLY IN THE 70S AT LOWER ELEVATIONS WITH LOCALLY WINDY
CONDITIONS BELOW PASSES AND CANYONS. CONFIDENCE IN THE FORECAST
BEYOND TUE IS LOW AS THE GFS HAS BEEN GOING BACK AND FORTH BETWEEN A
RIDGE ACROSS THE ERN PACIFIC (WHICH IS ALSO INDICATED ON THE ECMWF
AND CANADIAN) AND A SEMI-CUTOFF UPPER LOW WITH SOME MOISTURE IN IT.
CURRENT FORECAST TRENDS TOWARDS THE MORE CONSISTENT MODELS WHICH
KEEP THE AREA DRY WITH ABOVE NORMAL TEMPS THROUGH THU.
&&
.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...
SMALL CRAFT ADVISORY (SEE LAXMWWLOX).
HIGH SURF ADVISORY (SEE LAXCFWLOX).
&&
$$
PUBLIC...WOFFORD
AVIATION...MORRIS
SYNOPSIS...HOFFER
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