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

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000
FXUS66 KMTR 240045
AFDMTR

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SAN FRANCISCO BAY AREA
545 PM PDT TUE SEP 23 2014

.SYNOPSIS...AN APPROACHING UPPER LEVEL SYSTEM WILL BEGIN TO IMPACT
THE REGION ON WEDNESDAY, BRINGING RAIN CHANCES TO THE SAN
FRANCISCO BAY AREA THROUGH THURSDAY. AS A RESULT, DAYTIME
TEMPERATURES WILL ALSO FALL TO BELOW SEASONAL AVERAGES THROUGH THE
UPCOMING WEEKEND.

&&

.DISCUSSION...AS OF 02:37 PM PDT TUESDAY...THE FORECAST CONTINUES
TO FOCUS ON THE APPROACHING MID/UPPER LEVEL STORM SYSTEM
CURRENTLY CENTERED OVER THE PACIFIC NEAR 45N 137W. AS THE LOW
MOVES CLOSER TO THE BRITISH COLUMBIA COASTLINE IN THE NEXT 24
HOURS OR SO...DEEPER MOISTURE AHEAD OF THE SYSTEM WILL ADVECT INTO
THE PACIFIC NORTHWEST AND NORTHERN CALIFORNIA. AS A RESULT...LIGHT
RAIN WILL BEGIN TO DEVELOP ACROSS THE NORTHERN OFFSHORE WATERS AND
NORTH BAY REGION AS EARLY AS WEDNESDAY MORNING. PRECIPITATION
CHANCES WILL INCREASE THROUGH WEDNESDAY EVENING AND WILL SPREAD
SOUTHWARD AS THE UPPER LEVEL TROUGH DRAWS CLOSER TO THE WEST
COAST. RAIN SHOWERS WILL THEN BEGIN TO IMPACT THE ENTIRE SAN
FRANCISCO BAY AREA EARLY THURSDAY MORNING WITH ISOLATED SHOWERS
AS FAR SOUTH AS THE MONTEREY BAY AREA.

THE GREATEST RAINFALL AMOUNTS FROM THIS SYSTEM WILL BE OVER THE
NORTH BAY COASTAL MOUNTAINS WHERE 1/4" TO 1/2" WITH ISOLATED 3/4"
AMOUNTS ARE POSSIBLE. THE SAN FRANCISCO BAY METRO AREAS WILL
LIKELY PICK UP A FEW HUNDREDTHS UP TO A COUPLE TENTHS OF AN INCH.
MEANWHILE...AREAS FURTHER SOUTH WILL LIKELY ONLY RECEIVE A TRACE
TO A FEW HUNDREDTHS OF AN INCH DUE TO THE FAR NORTHERN TRACK OF
THE SYSTEM AS WELL AS FORECAST WEAKENING OF THE UPPER LOW. RAIN
CHANCES DIMINISH LATE THURSDAY AS WIND SPEEDS ALOFT BECOME
NORTHERLY AND DRIER AIR FILTERS INTO THE REGION. HOWEVER...CANNOT
RULE OUT A FEW LINGERING SHOWERS ON FRIDAY OVER THE NORTH BAY AS
SOME MOISTURE WRAPS AROUND THE CENTER OF THE LOW AS IT MOVES INTO
NORTHERN CALIFORNIA.

THE UPPER LEVEL SYSTEM WILL ALSO COOL DAYTIME TEMPERATURES TO
BELOW SEASONAL AVERAGES OVER THE BAY AREA ON WEDNESDAY...THEN
ACROSS THE ENTIRE REGION THURSDAY. COOLER TEMPERATURES WILL
PERSIST THROUGH THE WEEKEND AS THE TROUGH LINGERS ALONG THE WEST
COAST. THE TROUGH IS THEN FORECAST TO EJECT EASTWARD LATE IN THE
WEEKEND AND ALLOW FOR DRY WEATHER CONDITIONS RETURN. WITH THE
STORM TRACK FORECAST TO SHIFT WELL NORTH OF THE REGION EARLY NEXT
WEEK...TEMPERATURES WILL ALSO REBOUND TO NEAR SEASONAL AVERAGES.

&&

.AVIATION...AS OF 5:30 PM PDT TUESDAY...AN APPROACHING COLD FRONT
HAS STRENGTHENED THE ONSHORE GRADIENT WHICH HAS RESULTED IN
STRONGER ONSHORE FLOW AS WELL AS AN ANTICIPATED EARLIER ONSET OF
THE STRATUS THIS EVENING.

VICINITY OF KSFO...IFR CIGS EXPECTED TO RETURN EARLY THIS EVENING
AS THE ONSHORE GRADIENT STRENGTHENS. CIGS THIS EVENING MAY MOVE IN
WITH BREAKS IN THE STATUS POSSIBLE THROUGH 04Z. STRATUS EXPECTED
TO STAY IN AFTER 04Z. MODERATE TO LOCALLY STRONG AND GUSTY ONSHORE
FLOW EXPECTED THROUGH THIS EVENING. WINDS WILL EASE AND VEER
INCREASINGLY TO THE SOUTH OVERNIGHT.

KSFO BRIDGE APPROACH...SIMILAR TO KSFO.

MONTEREY BAY AREA TERMINALS...IFR CIGS EXPECTED TO RETURN EARLY
THIS EVENING AS THE ONSHORE GRADIENT STRENGTHENS. MODERATE TO
ONSHORE FLOW EXPECTED THROUGH THIS EVENING. WINDS WILL EASE
BECOMING LIGHT AND VARIABLE OVERNIGHT.

&&

.MARINE...AS OF 02:37 PM PDT TUESDAY...HIGH PRESSURE REMAINS OVER
THE EASTERN PACIFIC MAINTAINING LIGHT TO MODERATE NORTHWEST WINDS
THIS WEEK. A COLD FRONT WILL GO THROUGH THE AREA WEDNESDAY INTO
THURSDAY BRINGING A CHANCE OF RAIN AND INCREASED MODERATE PERIOD
NORTHWEST SWELL.

&&

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

$$

PUBLIC FORECAST: RGASS
AVIATION: CW
MARINE: AC

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