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

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000
FXUS66 KMTR 172100
AFDMTR

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SAN FRANCISCO BAY AREA
200 PM PDT WED SEP 17 2014

.SYNOPSIS...AN UPPER LEVEL SYSTEM WILL BEGIN TO IMPACT THE REGION
TONIGHT THROUGH THURSDAY NIGHT RESULTING IN AN INCREASED CHANCE FOR
RAIN SHOWERS AND A FEW THUNDERSTORMS. TEMPERATURES WILL ALSO COOL TO
BELOW SEASONAL AVERAGES THROUGH THE REMAINDER OF THE WORKWEEK. DRY
CONDITIONS RETURN AND TEMPERATURES REBOUND FOR THE UPCOMING WEEKEND
AS A RESULT OF BUILDING HIGH PRESSURE.

&&

.DISCUSSION...AS OF 01:58 PM PDT WEDNESDAY...GENERALLY CLEAR SKIES
PREVAIL ACROSS THE REGION THIS AFTERNOON WITH THE LEADING EDGE OF
THE MID/UPPER LEVEL TROUGH MOVING INTO NORTHERN CALIFORNIA.
CLOUDS FROM THIS SYSTEM CAN BE SEEN APPROACHING THE WEST COAST ON
VISIBLE SATELLITE IMAGERY AND RAIN IS ALREADY BEING REPORTED
ALONG THE COAST OF NORTHERN CALIFORNIA. RAIN CHANCES WILL BEGIN
TO INCREASE LATE THIS AFTERNOON OVER THE NORTH BAY AND WILL
SPREAD SOUTHWARD DOWN THE COAST THROUGH THE OVERNIGHT HOURS. IN
ADDITION...THERE IS A SLIGHT CHANCE OF THUNDERSTORMS LATE THIS
AFTERNOON AND EVENING OVER THE NORTH BAY WITH INCREASED
INSTABILITY AND STRENGTHENING UPPER LEVEL JET FORECAST TO SET UP
OVER NORTHERN CALIFORNIA.

OVERNIGHT...THE MID/UPPER LEVEL JET AND ASSOCIATED LOW WILL MOVE
INLAND AND SHIFT SOUTHEASTWARD SLIGHTLY. THIS WILL ALLOW FOR
PRECIPITATION TO SPREAD DOWN INTO THE SANTA CRUZ MOUNTAINS AND
OVER COASTAL LOCATIONS OF MONTEREY COUNTY. RAINFALL AMOUNTS WILL
BE GREATEST ACROSS THE WEST FACING COASTAL HILLS/MOUNTAINS WHERE
ISOLATED LOCATIONS COULD PICK A FEW TENTHS OF AN INCH.
MEANWHILE...INLAND VALLEY LOCATIONS MAY RECEIVE ONLY TRACE
AMOUNTS OR NO PRECIPITATION AT ALL OVERNIGHT. CHANCES FOR SHOWERS
WILL CONTINUE THROUGH EARLY TOMORROW AFTERNOON ACROSS THE NORTH
BAY AS A RESULT OF INCREASED MOISTURE AND THE UPPER LEVEL SYSTEM
MOVING ACROSS. WILL ALSO CARRY A SLIGHT CHANCE OF THUNDERSTORMS
OVER THE NORTH BAY AND EAST BAY HILLS/MOUNTAINS AGAIN TOMORROW
AFTERNOON. COOLER TEMPERATURES ALOFT WILL ALSO RESULT IN A
COOLING TREND THROUGH LATE WEEK.

RAIN CHANCES DIMINISH THURSDAY NIGHT WITH DRIER...OFFSHORE FLOW
DEVELOPING ALOFT AS THE MID/UPPER LEVEL TROUGH DROPS SOUTH OF THE
REGION. TEMPERATURES WILL REMAIN BELOW SEASONAL AVERAGES ON
FRIDAY WITH A SLIGHT WARMING TREND EXPECTED FOR THE UPCOMING
WEEKEND AND INTO EARLY NEXT WEEK WITH WEAK RIDGING BUILDING
ALOFT. THE LONGER RANGE MODELS CONTINUE TO HINT AT ANOTHER
MID/UPPER LEVEL TROUGH IMPACTING THE PACIFIC NORTHWEST AND
NORTHERN CALIFORNIA DURING THE MIDDLE OF NEXT WEEK. GIVEN THE
MODEL DIFFERENCES THIS FAR OUT...WILL KEEP DRY WEATHER CONDITIONS
AND NEAR NORMAL TEMPERATURES IN THE EXTENDED AT THIS TIME.
HOWEVER...WILL CONTINUE TO MONITOR THE LATEST FORECAST SOLUTIONS
IN THE COMING DAYS.

&&

.AVIATION...AS OF 10:30 AM PDT WEDNESDAY...LOW CLOUDS HAVE CLEARED
FROM THE TERMINALS BUT CONTINUE ALONG THE COAST AND MRY BAY. THE
APPROACHING UPPER TROUGH WILL BRING DEEPER LOW LEVEL MOISTURE TO
THE SFO BAY AREA TONIGHT. MODELS BRING LOWER CIGS INTO SFO AFTER
06Z WITH POSSIBLE LIGHT RAIN AFTER 12Z. WINDS WILL SWITCH TO THE
SOUTH TO SOUTHEAST LATE TONIGHT BUT REMAIN 10 KT OR LESS.

VICINITY OF KSFO...VFR THROUGH EARLY EVENING. MVFR CIGS AFTER 06Z
WITH POSSIBLE LIGHT RAIN. SOUTHWEST WINDS THROUGH THE DAY UNDER
15 KT. WINDS BECOMING SOUTH TO SOUTHEAST AFTER 07Z.

KSFO BRIDGE APPROACH...SIMILAR TO KSFO.

MONTEREY BAY AREA TERMINALS...BECOMING VFR. LOW CLOUDS ARE
EXPECTED TO LINGER OVER MRY BAY SO THERE WILL BE AN EARLY RETURN
INTO MRY AND SNS. IFR CIGS EXPECTED AT MRY AFTER 02Z AND SNS
AFTER 03Z.

&&

.MARINE...AS OF 01:58 PM PDT WEDNESDAY...A 997 MB LOW IS CENTERED
400 MILES WEST OF POINT ARENA. THIS LOW WILL MOVE THROUGH THE
NORTHERN WATERS ON THURSDAY RESULTING IN LIGHT SOUTHERLY WINDS
WITH A CHANCE OF SHOWERS. THERE WILL BE A SLIGHT CHANCE OF
THUNDERSTORMS THIS EVENING NORTH OF POINT REYES AND IN THE SAN
FRANCISCO BAY THURSDAY. WINDS WILL BECOME LIGHT TO MODERATE
NORTHWEST FRIDAY THROUGH SUNDAY AFTER THE LOW MOVES INLAND. A
LONG PERIOD SOUTHWEST SWELL WILL IMPACT THE WATERS THROUGH
THURSDAY.

&&

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

&&

$$

PUBLIC FORECAST: RGASS
AVIATION/MARINE: W PI

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