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

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000
FXUS66 KMTR 220008
AFDMTR

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SAN FRANCISCO BAY AREA
508 PM PDT TUE OCT 21 2014

.SYNOPSIS...DRY WEATHER CONDITIONS AND SEASONABLE TEMPERATURES WILL
PERSIST TROUGH WEDNESDAY WITH PRECIPITATION POSSIBLY RETURNING TO
THE NORTH BAY ON THURSDAY. RAIN CHANCES WILL THEN INCREASE AND
SPREAD SOUTHWARD FRIDAY NIGHT INTO SATURDAY AS AN UPPER LEVEL
SYSTEM MOVES THROUGH THE REGION.

&&

.DISCUSSION...AS OF 01:54 PM PDT TUESDAY...QUIET WEATHER CONDITIONS
ALONG WITH NEAR SEASONAL TEMPERATURES WILL PERSIST OVER THE
REGION THROUGH WEDNESDAY AS ZONAL FLOW CONTINUES ACROSS THE
REGION. MEANWHILE...THE FORECAST MODELS CONTINUE TO INDICATE A
DEEPER POOL OF MOISTURE THAT WILL ADVECT INTO THE PACIFIC
NORTHWEST/NORTHERN CALIFORNIA DURING THE LATTER HALF OF THE WEEK.
WEAK DISTURBANCES ARE ALSO FORECAST TO RIDE ALONG THE MEAN
FLOW...INTERACTING WITH THE ABUNDANT MOISTURE TO BRING RAINFALL
TO LOCATIONS NORTH OF OUR FORECAST AREA. BY THURSDAY
MORNING...THE MODELS SUGGEST THE DEEPER MOISTURE WILL DROP
SOUTHWARD OVER THE NORTH BAY AND BRING INCREASED CHANCES FOR
RAINFALL. HOWEVER...THERE WILL LIKELY BE A VERY DISTINCT CUT-OFF
FROM AREAS THAT WILL RECEIVE RAINFALL AND THOSE THAT WILL REMAIN
DRY. AT THIS TIME...THE BEST CHANCE THURSDAY THROUGH FRIDAY WILL
STAY NORTH OF THE GOLDEN GATE. WITH THIS...TEMPERATURES WILL BE A
BIT COOLER OVER NORTHERN AREAS WHILE INLAND PORTIONS OF THE
CENTRAL COAST WILL WARM SLIGHTLY THROUGH FRIDAY.

THERE IS GENERAL AGREEMENT WITH THE FORECAST MODELS THAT A
MID/UPPER LEVEL TROUGH WILL DEVELOP OFF THE PACIFIC NORTHWEST
COAST...PUSHING INLAND FRIDAY NIGHT INTO SATURDAY. THIS WOULD
DRIVE A FRONTAL BOUNDARY THROUGH THE FORECAST AREA AND INCREASE
CHANCE FOR PRECIPITATION ACROSS THE ENTIRE REGION. WHILE THE
MODELS AGREE ON THE TROUGH PUSHING INLAND...THEY CONTINUE TO
DIFFER ON THE AMOUNT OF AVAILABLE MOISTURE AS THIS TRANSITION
OCCURS. THE LATEST ECMWF KEEPS PRECIPITATION AMOUNTS LIGHT AS
SOUTHWEST FLOW DEVELOPS AHEAD OF THE APPROACHING TROUGH...DRYING
THE AIRMASS OUT AHEAD OF THE FRONTAL BOUNDARY. FOR NOW...WILL
KEEP THE BEST CHANCES FOR PRECIPITATION AND HIGHEST RAINFALL
AMOUNTS OVER THE NORTH BAY FRIDAY NIGHT INTO SATURDAY. WILL KEEP
A SLIGHT CHANCE OF PRECIPITATION INTO SATURDAY GIVEN TIMING
DIFFERENCES WITH THE MODELS AND LIKELIHOOD OF LINGERING MOISTURE
ACROSS THE REGION.

CONDITIONS DRY OUT SUNDAY AND MONDAY AS THE MID/UPPER LEVEL
TROUGH SHIFTS EASTWARD TOWARD THE ROCKIES AND NORTHWEST FLOW
DEVELOPS ALOFT. ALSO EXPECTING A SLIGHT WARMING TREND FOR EARLY
NEXT WEEK WITH ZONAL FLOW OVER THE REGION. ANOTHER MID/UPPER
LEVEL SYSTEM MAY BRING RAIN CHANCES BACK TO THE AREA BY THE
MIDDLE OF NEXT WEEK. SOMETHING WE WILL CONTINUE TO MONITOR AS THE
FORECAST MODELS COME INTO BETTER AGREEMENT...OR DIVERGE FURTHER.

&&

.AVIATION...AS OF 4:45 PM PDT TUESDAY...MAINLY CLEAR SKIES PREVAIL
WITH A FEW HIGH CLOUDS EXPECTED TO CONTINUE MOVING ACROSS THE
REGION THIS EVENING. MODERATE WINDS WILL EASE THIS EVENING
BECOMING LIGHT OVERNIGHT. THE LOW LEVEL MOISTURE SUGGESTS THAT
FOG OR LOW CLOUDS WILL DEVELOP AROUND 12Z. WILL INCLUDE MVFR
CONDITIONS IN PREVAILING GROUPS FOR NOW...BUT IT MAY BE MORE
OF  A PATCHY FOG SITUATION GIVEN THE RIDGE POSITION. MODERATE
CONFIDENCE.

VICINITY OF KSFO...VFR CONDITIONS THROUGH LATE TONIGHT. PATCHY LOW
CLOUDS AND FOG EXPECTED AFTER 14Z. MODERATE WEST WINDS WILL EASE
THIS EVENING BECOMING LIGHT OVERNIGHT.  MODERATE CONFIDENCE.

KSFO BRIDGE APPROACH...SIMILAR AS KSFO.

MONTEREY BAY AREA TERMINALS...VFR CONDITIONS THROUGH LATE
TONIGHT. PATCHY LOW CLOUDS AND FOG EXPECTED AFTER 09Z. LIGHT
ONSHORE FLOW WILL EASE THIS EVENING BECOMING LIGHT AND VARIABLE
OVERNIGHT. MODERATE CONFIDENCE.

&&

.MARINE...AS OF 04:57 PM PDT TUESDAY...MODERATE NORTHWEST WINDS
OVER THE COASTAL WATERS WILL PERSIST AS HIGH PRESSURE BUILDS OVER
THE EASTERN PACIFIC. THE STRONGEST WINDS WILL BE NEAR THE COAST
SOUTH OF POINT SUR. LARGE MODERATE PERIOD NORTHWEST SWELL WILL
CONTINUE TO MOVE THROUGH THE WATERS TODAY BEFORE DECREASING
TONIGHT. WINDS WILL SHIFT MORE SOUTHERLY BY TUESDAY AND WEDNESDAY
AS LOW PRESSURE MOVES INTO THE PACIFIC NORTHWEST.

&&

.MTR WATCHES/WARNINGS/ADVISORIES...
     .TNGT...SCA...PIGEON PT TO PT PINOS 0-10 NM UNTIL 11 PM
             SCA...ROUGH BAR ADVISORY FOR SF BAR UNTIL 3 AM
             SCA...PT PINOS TO PT PIEDRAS BLANCAS 0-10 NM

&&

$$

PUBLIC FORECAST: RGASS
AVIATION: CW
MARINE: JOHNSON

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