Small Craft Advisory 168, NWS San Francisco Bay Area, CA

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SAN FRANCISCO BAY AREA
237 PM PDT SAT OCT 20 2012

...RAINY AND BREEZY WEATHER SUNDAY NIGHT INTO MONDAY...

.DISCUSSION...AS OF 2:40 PM PDT SATURDAY...THANKS IN LARGE PART TO
A NORTHERLY SURFACE GRADIENT OVER 5 MB...CLOUDS HAVE CLEARED OUT
OF MOST OF THE CWA. ONE MAIN EXCEPTION IS AROUND MONTEREY BAY
WHERE THE NORTHERLY FLOW COMBINED WITH A WEAK LOW IN THE BAY HAS
PREVENTED THAT AREA FROM BECOMING CLOUD-FREE. HIGHS WILL END UP
MOSTLY IN THE 60S AND 70S AND BE ON AVERAGE 3 TO 6 DEGREES COOLER
THAN YESTERDAY.

MAIN WEATHER STORY CONTINUES TO BE CENTERED AROUND SUNDAY EVENING
THROUGH MONDAY AS A PIECE OF ENERGY ROTATING AROUND A STORM
COMPLEX STRETCHING FROM OFF THE BC COAST TO ALBERTA TAKES AIM ON
THE WEST COAST. THIS SYSTEM HAS PLENTY OF MOISTURE TO USE (PW
VALUE IN EXCESS OF AN INCH TO THE COAST) AND FAVORABLE DYNAMICS
(IMPRESSIVE AMOUNT OF POST- FRONTAL COLD AIR) PLUS A JET STREAK IN
EXCESS OF 100 MPH TO MAKE IT NOTEWORTHY. STILL LOOKS LIKE THE
PRIMARY EMPHASIS WILL BE LATE SUNDAY INTO MONDAY AS THE MAIN COLD
FRONT SWEEPS THROUGH OUR AREA. WITH PLENTY OF CAA PLUS MODERATE
WINDS ALOFT...LOCALLY BREEZY CONDITIONS ARE LIKELY. ALTHOUGH THE
MAJORITY OF RAINFALL WILL BE TO THE NORTH OF SF BAY....ALL SPOTS
WILL PROBABLY RECEIVE AT LEAST A TENTH OF AN INCH. ALSO INTERESTING TO
NOTE THAT A CHUNK OF THE MODELS DEVLOP A SURFACE LOW MORE TO THE
SOUTH AND HAVE AN ASSOCIATED PLUME OF MOISTURE/QPF GOING INTO THE
MONTEREY BAY REGION. IF THAT VERIFIES SOME OF OUR SOUTHERN SPOTS
(ESPECIALLY COASTAL RANGES) COULD END UP WITH HIGHER VALUES THAN
CURRENTLY EXPECTED.

BIGGEST IMPACTS OF THIS STORM LOOK TO FIRST BE THE MONDAY MORNING
COMMUTE AROUND THE BAY AREA -- ESPECIALLY IF THE FRONT GOES
THROUGH DURING THAT TIME. THE SECOND AREA OF CONCERN WILL BE FOR
THE NORTH AND EAST BAY MOUNTAINS WHERE WINDS LOCALLY ABOVE 40 MPH
WILL COMBINE WITH RAINFALL TO PRODUCE HAZARDOUS CONDITIONS --
INCLUDING THE POSSIBILITY OF TOPPLING SOME TREES. BY MONDAY
AFTERNOON WE COULD SEE MUCH AS AN INCH OVER THE NORTH BAY WITH
GENERALLY 1/4-1/2" FOR MOST URBAN LOCATIONS. THE COASTAL RANGES FOR
MONTEREY AND SANTA CRUZ COUNTY IS A TOUGH CALL AS IT GREATLY
DEPENDS ON THE SURFACE LOW DEVELOPING AND ITS POSITION. FOR
NOW...FEEL THAT 1/4-1/2" IS REASONABLE FOR THOSE SPOTS.

RAINFALL WILL DISSIPATE BEHIND THE FRONT ALTHOUGH A SECONDARY WAVE
LOOKS LIKELY FOR MONDAY EVENING/NIGHT WHICH SHOULD HELP TO DROP UP
TO ANOTHER 1/3" FOR HIGHER ELEVATION SPOTS WITH THE MAIN TARGET
OVER THE NORTH BAY. TEMPERATURES WILL ALSO START TO COOL BEHIND
THE FRONT WITH HIGHS ON MONDAY AND TUESDAY JUST IN THE 50S AND
60S.

A THIRD SHOT OF RAIN IS LOOKING MORE LIKELY FOR WEDNESDAY INTO
THURSDAY AS A PIECE OF ENERGY WILL ROTATE AROUND THE MAIN LOW OFF
THE PACNW COAST AND INTO NORCAL/OREGON. THERE IS SOME DISAGREEMENT
IF THE RAIN WILL MAKE IT FAR ENOUGH SOUTH TO IMPACT OUR CWA OR
STAY TO THE NORTH...FOR NOW WENT WITH HIGHER POP VALUES AS EVEN
THE DRIER MODELS SHOW RAINFALL VERY CLOSE.

FOR FRIDAY THROUGH THE WEEKEND...FAIRLY GOOD AGREEMENT THAT A
RIDGE WILL START TO BUILD BACK IN. THIS WILL LEAD TO WARMER
CONDITIONS ALONG WITH THE STORM TRACK BACK WELL TO THE NORTH.
&&

.AVIATION...AS OF 10:37 AM SATURDAY...THE MARINE LAYER IS
DEEP...AROUND 2000 FEET PER THE FORT ORD PROFILER...AND ONSHORE
FLOW HAS RAMPED UP. THUS...EXPECT LATE CLEARING MOST TERMINALS
TODAY. STRATUS IS EXPECTED TO REDEVELOP OVERNIGHT.

VICINITY OF KSFO...IFR CIGS ARE FORECAST TO LIFT TO MVFR BY
19Z...WITH VFR BY 20Z. MODERATE TO STRONG ONSHORE WINDS THIS
AFTERNOON...WITH POSSIBLE GUSTS NEAR 30 KT AT KSFO BETWEEN 22Z
TODAY AND 05Z SUNDAY.

KSFO BRIDGE APPROACH...APPROACH MAY BE IMPACTED THROUGH 21Z.

MONTEREY BAY AREA TERMINALS...IFR TO LIFR CIGS POSSIBLE THROUGH AT
LEAST 20Z. AN EARLY STRATUS RETURN IS ALSO EXPECTED.

&&

.MARINE...AS OF 10:37 AM PDT SATURDAY...SURFACE HIGH PRESSURE WILL
CONTINUE TO BUILD OVER THE EASTERN PACIFIC TODAY INTO SUNDAY. THIS
WILL RESULT IN MODERATE TO STRONG NORTHERLY WINDS OVER THE REGION.
WINDS WILL SIGNIFICANTLY INCREASE LATE THIS MORNING OVER THE
NORTHERN WATERS...WITH GUSTS TO 40 KT POSSIBLE THROUGH EARLY
SUNDAY MORNING. THESE STRONG WINDS WILL RESULT IN STEEP FRESH
SWELLS. WINDS WILL BEGIN TO SLOWLY SUBSIDE SUNDAY MORNING INTO
SUNDAY AFTERNOON.

BY LATE SUNDAY NIGHT INTO EARLY MONDAY MORNING...A STORM SYSTEM
WILL APPROACH THE REGION...RAPIDLY SWITCHING WINDS FROM THE NORTH
TO THE SOUTH. SOUTHERLY WINDS WITH GUSTS TO 30 KT WILL BE POSSIBLE
FOR A SHORT PERIOD OF TIME EARLY MONDAY.

MARINERS ARE ENCOURAGED TO CONTINUE TO MONITOR THE FORECAST
CLOSELY THROUGH THE WEEKEND INTO EARLY NEXT WEEK.

&&

.MTR WATCHES/WARNINGS/ADVISORIES...
     .TNGT...SCA...PIGEON PT TO PT PINOS 0-10 NM
             SCA...PIGEON PT TO PT PIEDRAS BLANCAS 10-60 NM
             GLW...PT ARENA TO PT REYES 0-10 NM
             GLW...PT ARENA TO PIGEON PT 10-60 NM
             SCA...PT PINOS TO PT PIEDRAS BLANCAS 0-10 NM
             SCA...PT REYES TO PIGEON PT 0-10 NM UNTIL 3 PM
             GLW...PT REYES TO PIGEON PT 0-10 NM
             SCA...SF BAY UNTIL 9 PM
             SCA...MRY BAY UNTIL 9 PM

&&

PUBLIC FORECAST: BELL/RWW
AVIATION/MARINE: SIMS

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