FXUS66 KMTR 270445
AFDMTR
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SAN FRANCISCO BAY AREA CA
845 PM PST THU NOV 26 2009
.DISCUSSION...AS OF 8:45 PM THURSDAY...INCREASING HIGH CLOUDS AHEAD
OF AN APPROACHING WEATHER SYSTEM...AS WELL AS WEAKENING OFFSHORE
FLOW...RESULTED IN MODEST COOLING ACROSS PORTIONS THE SAN FRANCISCO
BAY AREA TODAY...MAINLY THE NORTH BAY AND THE SF PENINSULA. EVEN
SO...TEMPERATURES REMAINED AT LEAST A FEW DEGREES ABOVE NORMAL IN
THOSE AREAS. FARTHER SOUTH...FROM SANTA CLARA AND SANTA CRUZ COUNTY
SOUTHWARD...PLENTY OF SUN ALONG WITH WARM ADVECTION RESULTED IN A
BALMY DAY. HIGH TEMPERATURES OF AT LEAST 70 DEGREES WERE COMMON...AND
EVEN SOME LOW TO MID 80S WERE RECORDED IN THE SALINAS VALLEY AND
SURROUNDING MOUNTAINS. TEMPERATURES ACROSS INTERIOR MONTEREY AND SAN
BENITO COUNTIES WERE AS MUCH AS 15 DEGREES ABOVE NORMAL.
MUCH COOLER CONDITIONS ARE EXPECTED TOMORROW AS A WEATHER SYSTEM
DROPS IN FROM THE NORTHWEST. MID AND HIGH LEVEL CLOUDS IN ADVANCE OF
THAT SYSTEM HAVE ALREADY BEGUN TO OVERSPREAD OUR AREA THIS EVENING
AND RAIN IS CURRENTLY BEING REPORTED ON THE FAR NORTHERN CALIFORNIA
COAST. THE 00Z NAM AND 00Z GFS AGREE THAT LIGHT RAIN WILL DEVELOP IN
THE NORTH BAY AFTER MIDNIGHT TONIGHT...AND PERHAPS SPREAD SOUTH OF
THE GOLDEN GATE BY SUNRISE. THE FRONT ITSELF IS QUITE WEAK AND WILL
WASH OUT OVER THE SF BAY AREA ON FRIDAY MORNING. BEHIND THE FRONT AN
UPPER LOW IS FORECAST TO PINCH OFF FROM THE SHARP UPPER TROUGH AND
DROP SOUTH OVER THE SF BAY AREA BY LATE FRIDAY AFTERNOON. THE
UNSTABLE AIRMASS WITH THE UPPER LOW WILL KEEP SCATTERED POST-FRONTAL
SHOWERS GOING THROUGH FRIDAY EVENING IN THE SF BAY AREA...AND THROUGH
FRIDAY NIGHT FROM MONTEREY BAY SOUTHWARD. THE 00Z NAM INDICATES THAT
A FEW SHOWERS MAY EVEN LINGER ACROSS THE FAR SOUTHERN PORTION OF OUR
REGION INTO EARLY SATURDAY MORNING. RAINFALL AMOUNTS THROUGH FRIDAY
NIGHT ARE EXPECTED TO BE LIGHT...GENERALLY LESS THAN A TENTH OF AN
INCH. PORTIONS OF THE NORTH BAY MAY PICK UP AS MUCH AS A QUARTER
INCH. CURRENT GRIDDED AND TEXT FORECASTS ACCURATELY REFLECT LATEST
OBSERVATIONAL DATA AND SHORT-TERM MODEL OUTPUT. NO EVENING UPDATES
WILL BE NEEDED.
ONCE THE LIGHT PRECIP EVENT ENDS ON FRIDAY NIGHT...ATTENTION WILL
TURN TO BRISK NORTHERLY WINDS THAT ARE FORECAST TO DEVELOP BY LATE
FRIDAY NIGHT...PARTICULARLY IN THE HILLS...AS A SURFACE HIGH BUILDS
RAPIDLY TO OUR NORTH ACROSS OREGON. BOTH THE NAM AND GFS FORECASTS
A RELATIVELY STRONG LOW LEVEL NORTHERLY JET OF ABOUT 50 KNOTS AT 925
MB LATE FRIDAY NIGHT INTO SATURDAY MORNING. THIS JET IS FORECAST TO
LIE OVER THE NORTH BAY AND PORTIONS OF THE EAST BAY. A WIND ADVISORY
MAY BE NEEDED FOR THE NORTH AND EAST BAY HILLS FROM LATE FRIDAY NIGHT
INTO SATURDAY. BRISK NORTH TO NORTHEAST WINDS WILL THEN CONTINUE
IN THE HILLS INTO SATURDAY NIGHT BEFORE DECREASING ON SUNDAY.
DAYTIME TEMPERATURES WILL WARM BACK ABOVE NORMAL OVER THE WEEKEND AS
A DRIER AND WARMER AIRMASS SPREADS OVER THE REGION. MOSTLY CLEAR
SKIES ARE EXPECTED THROUGH THE WEEKEND. ALTHOUGH BREEZY CONDITIONS
ARE FORECAST IN THE HILLS ON SATURDAY...THE LOWER ELEVATIONS SHOULD
BE SPARED FROM THESE BLUSTERY CONDITIONS FOR THE MOST PART. WINDS
WILL BE LIGHT IN ALL AREAS BY SUNDAY.
A HIGH AMPLITUDE RIDGE IS FORECAST TO RESIDE ALONG THE WEST COAST
OF NORTH AMERICA THROUGH MUCH OF NEXT WEEK. THIS RIDGE WILL LIKELY
MAINTAIN DRY CONDITIONS ACROSS OUR REGION...AS WELL AS ABOVE NORMAL
DAYTIME TEMPERATURES. HOWEVER...THE GFS CONTINUES TO HINT AT THE
DEVELOPMENT OF AT LEAST A PARTIAL BREAKTHROUGH OF THE WESTERLIES
UNDER THE RIDGE DURING THE SECOND HALF OF NEXT WEEK WHICH MAY MEAN
SOME WET WEATHER FOR OUR AREA BY THE END OF NEXT WEEK. THE ECWMF HAS
BEEN STEADFAST IN MAINTAINING DRY WEATHER WITH NO SIGNS OF A
BREAKTHROUGH DURING THE NEXT 7-9 DAYS. THE BREAKTHROUGH AND
DEVELOPMENT OF WET WEATHER IS MORE LIKELY TO DEVELOP BEYOND OUR
CURRENT FORECAST PERIOD...AND MOST LIKELY DURING THE SECOND WEEK IN
DECEMBER.
&&
.AVIATION...AS OF 4:15 PM PST THURSDAY...IMMEDIATE FORECAST CONCERN
IS WHERE DOES THE PATCHWORK OF STRATUS OVER THE INNER COASTAL WATERS
GO LATE THIS AFTERNOON AND EVENING? THIS IS A DAY WHEN SATELLITE
HELPS OUT TREMENDOUSLY SINCE THE MODELS ARE HAVING TROUBLE PICKING UP
ON THE WHEREABOUTS OF THE STRATUS FIELD. ALSO COMPLICATING TONIGHT'S
FORECAST IS THE INCOMING COLD FRONT WITH ITS OWN ABUNDANCE OF CLOUDS.
SO IN GENERAL FORECAST CONFIDENCE IS HIGHEST IN THE FIRST 0-6 HOURS
THEN FALLS OFF AFTER THIS.
KSFO TERMINAL AND SFO APPROACH...WEST WINDS 15-19 KNOTS UNTIL 03Z. A
RECENT CHECK ON THE PRESSURE GRADIENT FROM HALF MOON BAY TO KSFO IS
NEARLY FLAT SO WINDS MUST BE DUE TO A WEAK/DRY SHORTWAVE TROUGH
MOVING THROUGH THE AREA. A GRADUAL INCREASE IN CLOUDINESS IS EXPECTED
OVERNIGHT. FRONTAL PASSAGE PER THE LATEST GFS MODEL WOULD BE NEAR 12Z
FRIDAY MORNING. A FEW SHOWERS ASSOCIATED WITH THE FRONT WILL MOVE
THROUGH IN THE MORNING. VFR IS FORECAST FRIDAY. EXPECT GUSTY POST
FRONTAL NORTHWEST WINDS.
MRY BAY AREA TERMINALS...SATELLITE SHOWS THE STRATUS HAS LITERALLY
RUSHED TO KMRY IN THE LAST HOUR OR SO BUT A BREAK FROM IT IS POSSIBLE
LATER THIS EVENING AS A SMALL AREA OF CLEARING IS INDICATED UPSTREAM
TO THE NORTHWEST. LATER TONIGHT CHANCES FOR IFR CEILINGS GO UP AS
THE AIRMASS AHEAD OF THE INBOUND FRONTAL SYSTEM MOISTENS UP. WITH
THE ARRIVAL OF BETTER MIXING NEAR FRONTAL PASSAGE EARLY FRIDAY
MORNING IFR CLOUD LAYERS SHOULD LIFT BACK UP TO MVFR/VFR LEVELS.
THE POST FRONTAL AIRMASS SHOULD CLEAR OUT LEAVING VFR FOR FRIDAY.
EXPECT GUSTY NORTHWEST WINDS IN THE AFTERNOON AND EARLY EVENING.
&&
.MARINE...AS OF 4:15 PM THURSDAY...A RECENT SURGE IN NORTHWEST SWELL
WILL LEVEL OFF THIS EVENING AND POSSIBLY FALL A BIT OVERNIGHT BEFORE
PICKING BACK UP ON FRIDAY. SWELL PERIODS HAVE INCREASED TO 17-20
SECONDS SO SOME IMPRESSIVE SWELL SETS COULD COME IN FOR A WHILE
LONGER THIS EVENING. CARE SHOULD BE TAKEN IF VENTURING OUT TO THE
BEACHES AS UNEXPECTED LARGE SWELL SETS/RIP CURRENTS COULD PRESENT
PROBLEMS ESPECIALLY FOR VISITORS NOT FAMILIAR WITH WEST COAST SWELL
BEHAVIOR.
A HIGH SURF ADVISORY REMAINS VALID FOR THE ENTIRE COAST FROM 10 AM
FRIDAY THROUGH 4 AM SATURDAY FOR BREAKING WAVES IN EXCESS OF 15 FEET
ALONG THE COAST.
&&
.MTR WATCHES/WARNINGS/ADVISORIES...
.TNGT...NONE.
.FRI...HIGH SURF ADVISORY ON THE COAST 10 AM FRI THROUGH 4 AM
SATURDAY.
$$
PUBLIC FORECAST: DYKEMA
AVIATION/MARINE: CANEPA
NWS ON THE WEB AT WEATHER.GOV/SANFRANCISCO
