Area Forecast Discussion
Issued by NWS San Francisco Bay Area, CA

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000
FXUS66 KMTR 020344
AFDMTR

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SAN FRANCISCO BAY AREA
844 PM PDT TUE SEP 1 2015

.SYNOPSIS...ASIDE FROM THE POSSIBILITY OF COASTAL DRIZZLE TONIGHT
INTO WEDNESDAY MORNING...DRY WEATHER CONDITIONS WILL PERSIST
THROUGH THE UPCOMING WEEKEND. TEMPERATURES WILL COOL THROUGH LATE
WEEK AS AN UPPER LEVEL TROUGH DIGS SOUTHWARD INTO THE PACIFIC
NORTHWEST. WARMER AND DRIER CONDITIONS RETURN FOR THE UPCOMING
WEEKEND.

&&

.DISCUSSION...AS OF 8:44 PM PDT TUESDAY...ANOTHER MILD EVENING
ANTICIPATED TONIGHT WITH TEMPERATURES CURRENTLY RUNNING IN THE
LOWER TO MID 60S ALONG THE COAST TO MID 70S INLAND. SATELLITE
IMAGERY SHOWS A STRIP OF STRATUS ALONG THE COAST EXTENDING SOUTH
FROM HALF MOON BAY. PATCHY STRATUS IS ANTICIPATED ONCE AGAIN
TONIGHT WITH LOCALIZED DRIZZLE IN RESPONSE TO AN APPROACHING UPPER
LEVEL DISTURBANCE THAT IS EXPECTED TO FURTHER DEEPEN THE MARINE
LAYER.

COOLER TEMPERATURES ARE IN STORE WEDNESDAY AS THE WEAK UPPER LEVEL
SHORT WAVE SWINGS ACROSS THE REGION. THE COOLING TREND WILL
CONTINUE THROUGH THE LATER HALF OF THE WEEK AS THE LONGWAVE
TROUGH DIGS SOUTH OVER THE PACIFIC NORTHWEST INTO NORTHERN
CALIFORNIA INTRODUCING A COOLER AIRMASS ACROSS THE NORTHERN HALF
OF THE STATE. 850 MB TEMP AND 500 MB HEIGHTS WILL PLUMMET THROUGH
THE END OF THE WEEK REACHING A LOW OF 8.5 C AND 269 DAM FRIDAY
NIGHT. THIS WILL TRANSLATE INTO HIGHS IN THE 60S ALONG THE COAST
AND 70S INLAND WITH LOWS IN THE 50S OVER LOW LYING AREAS AND 40S
OVER HIGHER ELEVATIONS.

THIS SYSTEM IS FORECAST TO KICK OUT TO THE NORTHEAST ON SATURDAY
AND WILL BE REPLACED BY AN AREA OF HIGH PRESSURE BUILDING IN FROM
THE WEST. THIS WILL KICK START A WARMING TREND THAT IS FITTING
OF THE LABOR DAY WEEKEND. FURTHER WARMING IS ANTICIPATED SUNDAY
AND MONDAY AS A THERMAL TROUGH SETS UP OVER THE STATE THEN SHIFTS
WEST OVER THE COAST. WARM AND DRY CONDITIONS WILL PERSIST THROUGH
EARLY NEXT WEEK WITH NO RAIN IN THE FORECAST THROUGH NEXT WEEK.

FORECAST APPEARS ON TRACK...NO UPDATE NEED AT THIS TIME.

&&

.AVIATION...AS OF 5:25 PM PDT TUESDAY...PATCHY COASTAL STRATUS
SEEN FROM SOUTHERN MARIN COUNTY TO NORTHERN MONTEREY COUNTY
OTHERWISE VFR. THE FORECAST AREA IS ON THE BOUNDARY BETWEEN VERY
WEAK UPPER LEVEL SW AND NW WINDS CAUSING A NARROW BUT LONG BAND OF
CIRRUS SEEN ON THE VISIBLE IMAGERY.

A FAIRLY DECENT SMX-SFO PRESSURE GRADIENT IS PERSISTING SINCE LATE
LAST EVENING...PRESENTLY 2 MB. NW WINDS OVER THE INNER COASTAL
WATERS ARE TENDING TO WEAKEN BECAUSE OF THIS SOUTH-NORTH DIRECTED
GRADIENT. ONSHORE WINDS WILL PERSIST THIS EVENING HOWEVER...DRIVEN
BY A SLOWLY INCREASING SFO-SAC GRADIENT PRESENTLY 2.4 MB.

STRATUS AND FOG ARE EXPECTED TO INCREASE TONIGHT WITH INCREASING
INLAND INTRUSION...BUT MAINLY LATE TONIGHT INTO WEDNESDAY MORNING.
THE GFS MODEL IS CONSISTENT WITH FORECASTING A FAIRLY VIGOROUS
LOW-LEVEL TROUGH OVER THE EPAC TO SLIDE SOUTHWARD OVER THE COASTAL
WATERS TOMORROW. INCREASING BOUNDARY LAYER HUMIDITY OVERNIGHT INTO
WEDNESDAY MORNING COUPLED WITH LOWER LEVEL COOLING WILL LIKELY
ENHANCE STRATUS CLOUD COVER POSSIBLY CAUSING A FEW LOCALIZED
POCKETS OF DRIZZLE.

MESOSCALE MODEL PREDICTS 3-4 MB ACV-SFO GRADIENT WEDNESDAY INTO
WEDNESDAY NIGHT BUT GIVEN BACK-DROP OF THE MID-WEEK WEATHER
PATTERN WOULD NOT BE SURPRISED IF IT BECAME A BIT STRONGER. IF IT
DOES W-NW WINDS WILL TEND TO BE A BIT GUSTIER THAN ADVERTISED AND
SKIES WILL TEND TO CLEAR OUT FASTER FROM NORTH-SOUTH WED EVENING
AND NIGHT.

VICINITY OF KSFO...VFR. INCREASING MARINE LAYER DEPTH FORECAST DURING
THE PERIOD. MVFR CIGS BEGINNING EARLY WED MORNING...BUT LESS
CONFIDENT ABOUT HOW LONG CIGS WILL LAST AT KSFO WED. FEW-SCT014-015
FORECAST LATE MORNING THROUGH AFTERNOON. MODEL GUIDANCE INDICATES
GUSTY WESTERLY WINDS WED AFTERNOON AND EVENING SUSTAINED AND GUSTS
UP OVER 20 KNOTS.

KSFO BRIDGE APPROACH...SIMILAR TO KSFO.

MONTEREY BAY AREA TERMINALS...SW-W WIND FLOW INTO THE MONTEREY BAY
WITH STRATUS CLOUDS GRADUALLY APPROACHING THE TERMINALS THIS
EVENING. IFR CIGS FORECAST TO DEVELOP 03Z-06Z...IFR PREVAILING
OVERNIGHT. MVFR CIGS LATE WED MORNING WITH PARTIAL CLEARING BY WED
AFTERNOON.

&&

.MARINE...AS OF 1:51 PM PDT TUESDAY...A WEAK SURFACE PRESSURE
GRADIENT WILL MAINTAIN GENERALLY LIGHT WINDS OVER A GOOD PORTION
OF THE COASTAL WATERS THROUGH WEDNESDAY AFTERNOON. MODERATE WINDS
ARE HOWEVER EXPECTED TO PERSIST OVER THE NORTHERN OUTER COASTAL
WATERS THROUGH TONIGHT. THE SURFACE PRESSURE GRADIENT IS EXPECTED
TO INCREASE FOR THE SECOND HALF OF THE WEEK...RESULTING IN
STRENGTHENING WINDS.

&&

.MTR WATCHES/WARNINGS/ADVISORIES...
     .TNGT...SCA...PT ARENA TO PIGEON PT 10-60 NM UNTIL 2 AM
             SCA...PIGEON PT TO PT PIEDRAS BLANCAS 10-60 NM UNTIL 2 AM
             SCA...SF BAY UNTIL 8 PM

&&

$$

PUBLIC FORECAST: CW
AVIATION: CANEPA
MARINE: LARRY


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