FXUS66 KMTR 252358
AFDMTR

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SAN FRANCISCO BAY AREA CA
400 PM PST WED NOV 25 2009

.DISCUSSION...AS OF 3:00 PM WEDNESDAY...HIGHER PROBABILITIES BUT
LIGHT AMOUNTS OF RAIN OVER THE NORTH BAY COUNTIES THANKSGIVING
EVENING AND VERY EARLY FRIDAY MORNING. GUSTY WINDS LATE FRIDAY AND
EXTENDING INTO SATURDAY. HIGH SURF POTENTIAL FOR FRIDAY AFTERNOON.

WITH HIGH PRESSURE OVER THE WESTERN UNITED STATES AND SURFACE LIGHT
OFFSHORE WINDS TEMPERATURES VARY FROM LITTLE CHANGE TO UP 4 DEGS
GENERALLY AROUND THE FORECAST AREA THIS AFTERNOON BENEATH SUNNY
SKIES AND MILD DOWN-SLOPE WARMING CONDITIONS. GENERALLY TEMPERATURES
ARE IN THE 60S OVER MUCH OF THE FORECAST AREA WITH A FEW READINGS TO
NEAR 70 IN INLAND COASTAL VALLEYS...AND A FEW READINGS INTO THE MID
70S AT WARMEST LOCATIONS IN SOUTHERN MONTEREY COUNTY. WINDS OVER THE
HIGHER ELEVATIONS GENERALLY NORTHEAST AT 15-20 MPH AT POST TIME.

THROUGH EARLY THANKSGIVING MORNING...HIGH PRESSURE AT THE SURFACE
OVER THE GREAT BASIN COMBINED WITH A TROF OF LOW PRESSURE OVER THE
CALIFORNIA COAST WILL MAINTAIN OFFSHORE WIND TENDENCIES. WINDS WILL
CONTINUE TO VEER AS THE GREAT BASIN SURFACE HIGH SLIPS EASTWARD AND
PRESSURE BEGINS TO FALL AHEAD OF AN APPROACHING GULF COLD-FRONT.
WITH LATE AFTERNOON CLOUDINESS TEMPERATURES THURSDAY WILL BE A FEW
DEGS LOWER.

HAVE INCREASED PRECIP PROBABILITIES TO LIKELY CATEGORY FOR THE
THURSDAY EVENING TIME PERIOD OVER THE MARIN AND SONOMA COUNTY AREAS
CONSIDERING TIME OF YEAR AND RELATIVELY GOOD AGREEMENT AMONGST THE
SHORT AND MEDIUM RANGE MODELS FOR A COLD-FRONTAL PASSAGE DURING THE
THURSDAY NIGHT/FRIDAY MORNING TIME PERIOD. MODELS NOW SHOWING THE
FRONT PUSHING THROUGH THE CENTRAL COAST FORECAST AREA BY FRIDAY
MORNING BUT TRENDING TOWARD SLOWING THE UPPER TROF BY FRIDAY
AFTERNOON. 18Z NAM DEVELOPS CLOSED LOW AS OF 09Z FRIDAY NIGHT AND
EVEN THE ECMWF AND GFS DEVELOP A VERY OPEN WAVE HINTING TOWARD SOME
CLOSED CIRCULATION LATE FRIDAY NIGHT JUST SOUTHEAST OF MONTEREY/SAN
BENITO COUNTY. NONETHELESS...PRECIP PROBABILITIES IN LIKELY CATEGORY
NORTH BAY AREA BUT QUANTITY THE ORDER OF A FEW HUNDREDTHS AND MAYBE A
TENTH OR TWO IN THE HEAVIEST PRECIP AREAS.

ADDITIONAL FRIDAY CONCERN IS THE ARRIVAL OF A LARGE WAVE TRAIN
SPREADING DOWN THE COAST. HAZARDOUS WEATHER OUTLOOK HAS BEEN ISSUED
TO REFLECT THREAT FOR HOLIDAY VISITORS TO THE CENTRAL COAST FROM THIS
LARGE AND HIGH ENERGY SWELL. ANY FORMAL HIGH SURF ADVISORY WILL BE
ISSUED EARLY THANKSGIVING DAY SHOULD MODELS MAINTAIN CONSISTENCY.

POST-FRONT COLD AIR ADVECTION TO LOWER TEMPERATURES TO LESS THAN
SEASONAL READINGS FRIDAY AND TO A LESSER EXTENT SATURDAY. PRECIP
CHANCES DIMINISH AFTER FRIDAY MID-DAY FOR THE CENTRAL COAST AS
VERTICAL MOTION PRIMARILY SOUTHEAST PORTION OF FORECAST AREA IN
PROXIMITY OF TROF/LOW OVER INTERIOR CENTRAL/SOUTH CALIFORNIA. WIND
FLOW ALOFT TURNS NORTH AND EVENTUALLY NORTHEAST AT LOWER LEVELS
SUNDAY AS HIGH AMPLITUDE RIDGE ALOFT DEVELOPS IMMEDIATELY ALONG THE
CALIFORNIA COAST WITH HIGH PRESSURE AGAIN BUILDING INTO THE PACIFIC
NORTHWEST. LOOK FOR TEMPERATURES TO REBOUND TO NORMAL AND SLIGHTLY
ABOVE AT THE FIRST OF THE WEEK.

FOR THE PERIOD NEXT THURSDAY THROUGH NEXT WEEKEND...THE 12Z ECMWF
COMING INTO AGREEMENT WITH THE GFS WHICH REFLECTS SOME DEGREE OF
ZONAL FLOW BREAKING BENEATH THE FAVORED RIDGE AXIS OVER THE EAST
PACIFIC AND ALONG THE WEST COAST. WILL NEED TO MONITOR AND CONSIDER
DEVELOPING LINK OF THAT ZONAL FLOW WITH RELEASED MOISTURE FROM
STRONG CYCLONE NIDA FOR PRECIP THREAT FOR THE S.F.BAY AREA AND
CENTRAL COAST FOR DEC 5TH WEEKEND.

&&

.AVIATION...AS OF 4:00 PM PST WEDNESDAY...CLEAR SKIES AND LIGHT
OFFSHORE FLOW WILL CONTINUE THROUGH TONIGHT AS THE REGION REMAINS
UNDER THE INFLUENCE OF HIGH PRESSURE. SOME PATCHY GROUND FOG IS
EXPECTED TO REDEVELOP AROUND KSTS TONIGHT.

ALL TERMINALS(EXCEPT KSTS)...VFR CONDITIONS EXPECTED THROUGH
WEDNESDAY WITH LIGHT WINDS.

&&

.MTR WATCHES/WARNINGS/ADVISORIES...
    .TNGT...NONE.

$$

PUBLIC FORECAST: GUDGEL
AVIATION/MARINE: CW

NWS ON THE WEB AT WEATHER.GOV/SANFRANCISCO