FXUS66 KMTR 280406
AFDMTR

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SAN FRANCISCO BAY AREA CA
805 PM PST FRI NOV 27 2009

.DISCUSSION...AS OF 7:45 PM FRIDAY...SCATTERED SHOWERS AND ISOLATED
LIGHTNING STRIKES WERE THE THEME THIS AFTERNOON IN AN UNSTABLE POST
COLD FRONTAL AIRMASS. KMUX RADAR SHOWS SOME SHOWERS CONTINUING OVER
THE AREA WITH A RECENT REPORT OF PEA SIZED HAIL IN CONTRA COSTA
COUNTY.

THE TROUGH AND ITS ASSOCIATED COLD POOL OF AIR AT 500 MB WILL SLIDE
SOUTH AND EAST TO SOCAL BY SATURDAY PER MOST RECENT MODEL DATA.
MODIFIED SOUNDINGS HAD INDICATED CAPE VALUES BETWEEN 200-275 J/KG
EARLIER THIS AFTERNOON BUT LOW LEVEL WIND SHEAR WAS NIL DUE TO A
SOLID NORTH TO NORTHWEST WIND FLOW THROUGH THE LOW LEVELS JUST
ABOUT EVERYWHERE. SURFACE BASED CONVECTION HAS EASED WITH THE LOSS
OF WHAT DAYTIME HEATING THERE WAS TODAY BUT ISOLATED CONVECTION
REMAINS POSSIBLE FOR A FEW MORE HOURS TONIGHT AS 850-500 MB LAYER
LAPSE RATES REMAIN STEEP.

THE NEXT ISSUE TO FOCUS ON WILL BE THE WINDS...IN PARTICULAR THE
STRENGTH AND DURATION OF WINDS LATE TONIGHT AND SATURDAY. GALES ARE
POSTED FOR THE OUTER COASTAL WATERS AND NORTHERN INNER WATERS. FOR
LAND ZONES THE QUESTION IS HOW STRONG THE WINDS WILL BECOME. THE
MODELS SHOW THE STRONGEST NORTHERLY PRESSURE GRADIENTS OVER THE
WATERS FROM ARCATA TO SAN FRANCISCO...MORE OR LESS RANGING FROM
9-10 MB TONIGHT THROUGH SATURDAY. A STRONG GRADIENT LIKE THIS
COMBINED WITH GOOD WIND LINKAGE THROUGH THE LOW LEVELS WILL LIKELY
CAUSE AREAS OF GUSTY WINDS TO OVERLAP THE IMMEDIATE COASTLINE AS
WELL. AREAS OF GUSTY WINDS ARE ALSO POSSIBLE OVER THE NORTH BAY
HILLS/MTNS.

FOR THE REMAINDER OF THE WEEKEND AND NEXT WEEK DRY WEATHER WILL
LIKELY PREVAIL. HIGH PRESSURE WILL BUILD IN TONIGHT AND SATURDAY.
A STRONG NORTHERLY COMPONENT TO THE WIND WILL HELP CLEAR OUT THE
CLOUDS QUICKLY SATURDAY...LEADING TO A SUNNY TO MOSTLY SUNNY DAY.
THIS TYPE OF PATTERN OFTEN PRECLUDES A STRATUS RETURN AS WELL FOR AT
LEAST A FEW DAYS OR MORE. OVERALL MAINLY CLEAR WEATHER SHOULD
CONTINUE INTO NEXT WEEK WITH A GRADUAL RECOVERY IN TEMPERATURES.

&&

.AVIATION...AS OF 8:05 PM PST FRIDAY...AREAS OF SHOWERS AND ISOLATED
THUNDERSTORMS HAVE MOVED SOUTH OF THE BAY AREA THIS EVENING. SHOWERS
ARE EXPECTED TO CONTINUE SOUTHWARD ACROSS THE SOUTHERN HALF OF THE
REGION THROUGH THIS EVENING. SKIES WILL CLEAR OUT BEHIND THE FRONTAL
SYSTEM AS IT MOVES SOUTH. AFTER 09Z LOW-LEVEL WIND SHEAR IS
POSSIBLE DUE TO NNE WINDS 30-40KTS AT 850MB/5000-FT LEVEL.

VICINITY OF KSFO...VFR CONDITION EXPECTED TONIGHT THROUGH SATURDAY
WITH THE POSSIBILITY OF LOW LEVEL WIND SHEAR AFTER 09Z TONIGHT DUE
TO GUSTY WINDS OF 30-40KT AT 5000 FEET BY DAWN.

KSFO BRIDGE APPROACH...SAME AS KSFO.

MRY BAY AREA TERMINALS...VFR CIGS WITH GUSTY WINDS EXPECTED THROUGH
TONIGHT AS THE REMNANTS OF THE FRONTAL PASSAGE FROM EARLIER TODAY
MOVE SOUTH OVER THE REGION. SKIES WILL CLEAR OUT OVERNIGHT ONCE THIS
DISTURBANCE PASSES.

&&

.MARINE...AS OF 10:15 AM FRIDAY...MODELS CONTINUE TO SHOW SEAS
INCREASING TO 15-18 FEET LATER TODAY SO A HIGH SURF ADVISORY UPDATED
FOR VALID TIME BY THIS AFTERNOON THROUGH 4 PM SATURDAY. SWELL PERIODS
SHOULD BE IN THE 14-15 SECONDS RANGE SO SOME IMPRESSIVE SWELL SETS
ARRIVING AS HOLIDAY WEEKEND CONTINUING. 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. ADDITIONALLY...GALE FORCE WINDS
ESPECIALLY OVER THE OUTER CENTRAL COAST WATERS IN POST-FRONTAL
ENVIRONMENT.

&&

.MTR WATCHES/WARNINGS/ADVISORIES...
    .TNGT...HIGH SURF ADVISORY ON THE COAST TONIGHT THROUGH 4 PM
           SATURDAY.
        ...GALE WARNING...PT ARENA TO PIGEON PT 0-10 NM
                          PT ARENA TO PT PIEDRAS BLANCAS 10-60 NM
        ...SCA...PIGEON PT TO PT PIEDRAS BLANCAS 0-10 NM
                 SFO AND MRY BAYS
        ...SCA FOR ROUGH BAR...SF BAR

$$

PUBLIC FORECAST: CANEPA
AVIATION/MARINE: CW

NWS ON THE WEB AT WEATHER.GOV/SANFRANCISCO