000
FXUS66 KMTR 131731
AFDMTR

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SAN FRANCISCO BAY AREA
1031 AM PDT MON MAY 13 2013

.DISCUSSION...AS OF 8:50 AM PDT MONDAY...APPROACHING LONGWAVE TROF
FROM THE WEST WILL HELP TO BOOST THE MARINE LAYER (CURRENTLY
AROUND 1000 FEET) LATER TODAY. DID A MINOR FORECAST UPDATE TO
REMOVE SOME CLOUDS FROM THE MONTEREY BAY REGION PLUS HOLLISTER
VALLEY TO BETTER DEPICT THE CURRENT PATTERN. ONLY OTHER POSSIBLE
UPDATE WOULD BE IF THE COOL DOWN DOES NOT KICK IN AS QUICK AS
FORECAST WHICH WOULD LET TEMPS EXCEED THEIR FORECAST HIGHS.
WESTERLY SURFACE FLOW IS EXPECTED TO INCREASE TO AROUND 3.5 MB BY
THIS AFTERNOON WHICH SHOULD HELP, HOWEVER THE NORTHERN COMPONENT
WILL JUMP UP TO AROUND 7 MB.

DEFINITELY AGREE THAT TOMORROW WILL BE COOLER AS 500 MB HEIGHTS
DROP FROM 583 DM TO 575 DM AS A WEAK UPPER LOW MOVES TO OUR CWA.

.PREVIOUS DISCUSSION...MAIN WEATHER STORY FOR TODAY WILL BE
COOLER TEMPERATURES THIS AFTERNOON.

SHORT TERM...THE MARINE LAYER CONTINUES TO HOLD STEADY AROUND
1000 FEET AS LOW CLOUDS HAVE BEEN SOMEWHAT SLOW TO SPREAD INLAND
EVEN WITH A 3.1 MB ONSHORE GRADIENT FROM SFO-SAC. THE UPPER TROUGH
OFF THE COAST THAT WAS EXPECTED TO DEEPEN THE MARINE INVERSION
LAYER HAS SLOWED SLIGHTLY AS ITS BUMPED INTO THE RIDGE THAT
BROUGHT THE NICE WEATHER OVER THE WEEKEND. THE SHORTWAVE TROUGH CAN
BE SEEN ON WATER VAPOR JUST ABOUT TO PASS OVER 35N/130W. THIS
FEATURE WILL CONTINUE TO APPROACH TODAY AND WE SHOULD SEE THE
MARINE LAYER DEEPEN THROUGH THE DAY TO AT LEAST 1500 FEET BY THIS
AFTERNOON AND 2000 FEET LATER THIS EVENING AND OVERNIGHT. AS
HEIGHTS FALL AND 850 MB TEMPS LOWER THE SEA-BREEZE SHOULD BE MORE
PRONOUNCED AROUND THE BAY AND COASTAL VALLEYS AND LEAD TO
NOTICEABLY COOLER INLAND TEMPERATURES THIS AFTERNOON. HOWEVER...IN
GENERAL EXPECT ANOTHER NICE SPRING DAY ACROSS MOST OF THE
DISTRICT. EXCEPTION WILL BE THE COAST AND CITY WHERE CLOUDS WILL
LINGER MOST IF NOT ALL OF THE DAY WITH THE DEEPENING MARINE LAYER
AND INCREASING ONSHORE WINDS.

THE MAIN VORTICITY MAXIMA WILL PASS RIGHT OVER THE BAY AREA
TONIGHT INTO EARLY TUESDAY MORNING. THUS LOCAL COASTAL AND
HILLSIDE DRIZZLE WILL LIKELY BE REPORTED ALONG THE HWY 1 CORRIDOR
AND LOCATIONS SUCH AS THE SANTA CRUZ MTNS BY TUESDAY MORNING.
TEMPERATURE TREND FOR TUESDAY WILL LIKELY SHOW CONTINUED COOLING
BUT NOT AS DRAMATIC AS WHAT IS FORECAST FOR THIS AFTERNOON.

A ZONAL OR SLIGHTLY CYCLONIC FLOW SETS UP FROM MIDWEEK AND INTO
NEXT WEEKEND. THE ECMWF IS MOST BULLISH IN DROPPING THE NEXT COLD
FRONT INTO FAR NORTHERN CALIFORNIA BY LATER THURSDAY INTO FRIDAY.
PRECIP CHANCES WILL BE POSSIBLE TO OUR NORTH...CLOSER TO THE
OREGON BORDER AND IN THE SIERRA BUT NOT EXPECTING ANY RAIN/SHOWERS
FOR THE BAY AREA THIS WEEK. THAT FEATURE WILL KEEP TEMPERATURES
NEAR OR SLIGHTLY BELOW NORMAL. THE UPPER TROUGH WILL BRING 850 MB
TEMPS DOWN TO AROUND 7-9 CELSIUS THURSDAY INTO FRIDAY WHICH SHOULD
PREVENT THE MARINE INVERSION FROM BECOMING TOO ENTRENCHED AND
PROMOTE AFTERNOON SUNSHINE...EVEN NEAR THE COAST.

AS THAT TROUGH MOVES INLAND BY NEXT WEEKEND THE ECMWF BUILDS A
RIDGE WITH SOME HINT OF NORTHERLY WINDS ACROSS NORTHERN
CALIFORNIA. HOWEVER THE GEM AND GFS MODELS ARE NOT IN COMPLETE
AGREEMENT. ITS GETTING TO THE TIME OF YEAR WHERE PERSISTENCE AND
CLIMATOLOGY CAN BE BETTER FORECAST TOOLS THAN THE MODELS. NO BIG
WEATHER CHANGES FORECAST OVER THE NEXT 7 DAYS.

&&

.AVIATION...AS OF 10:30 AM PDT MONDAY...TRICKY FORECAST THIS
MORNING AS INCREASING ONSHORE FLOW AND A DEEPENING MARINE LAYER
HAS CREATED AN EBB AND FLOW SCENARIO. STRATUS JUST REMAINED TO THE
WEST OF A FEW AIRPORTS AND THEN RECENTLY PUSHED IN (1630Z) AND NOW
LAST VIS SATELLITE (1710Z) SHOWS THINNING. NEEDLESS TO SAY...LOW
CONFIDENCE FORECAST THROUGH 18-19Z. GENERAL THINKING IS THAT
STRATUS WILL GRADUALLY DIMINISH BY 18Z. GUSTY ONSHORE FLOW THIS
AFTERNOON WITH WINDS OVER 20 KTS AT TIMES. STRATUS AND MARINE
LAYER RETURN TONIGHT.

VICINITY OF KSFO...WILL FORECAST VFR CONDITIONS FOR KSFO BY TAF
VALID TIME. KOAK ON THE OTHER HAND MAY LINGER A LITTLE AFTER 18Z.
OTHERWISE...WIND GUSTS UP TO 30 KT POSSIBLE THIS AFTERNOON. CIGS
RETURN TONIGHT AFTER 05-06Z.

KSFO BRIDGE APPROACH...CIGS SEEM TO BE MAINLY CONFINED NORTH OF
THE APPOACH. A FEW LINGERING CLOUDS POSSIBLE THROUGH 18Z.

MONTEREY BAY AREA TERMINALS...CIGS WILL LINGER AROUND KMRY...BUT
KSNS IS IN THE CLEAR. CIGS RETURN EARLY TONIGHT.

&&

.MTR WATCHES/WARNINGS/ADVISORIES...
     .TDAY...SCA...PIGEON PT TO PT PINOS 0-10 NM FROM NOON
             SCA...PT REYES TO PIGEON PT 0-10 NM FROM 3 PM
             SCA...PT ARENA TO PIGEON PT 10-60 NM FROM 3 PM
             SCA...PT PINOS TO PT PIEDRAS BLANCAS 0-10 NM
             SCA...PIGEON PT TO PT PIEDRAS BLANCAS 10-60 NM
             SCA...PT ARENA TO PT REYES 0-10 NM FROM NOON
             SCA...SF BAY FROM 1 PM

&&

$$

PUBLIC FORECAST: BELL/RWW
AVIATION/MARINE: MM

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