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

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000
FXUS66 KMTR 031738
AFDMTR

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SAN FRANCISCO BAY AREA
1038 AM PDT SUN MAY 3 2015

.SYNOPSIS...A RELATIVELY DEEP MARINE LAYER AND PERSISTENT ONSHORE
FLOW WILL MAINTAIN AREAS OF NIGHT AND MORNING LOW CLOUDS THROUGH
THE MIDDLE OF THE WEEK...ALONG WITH TEMPERATURES NEAR TO SLIGHTLY
BELOW NORMAL. AN UPPER LEVEL LOW IS THEN FORECAST TO DEVELOP OVER
CALIFORNIA BY THURSDAY. THIS LOW WILL MIX OUT THE MARINE
LAYER...BUT ALSO MAINTAIN RELATIVELY COOL WEATHER CONDITIONS INTO
THE SECOND HALF OF THE WEEK. THERE IS ALSO A SLIGHT CHANCE OF
SHOWERS WITH THIS WEATHER SYSTEM...MAINLY ACROSS THE SOUTHERN
PORTION OF OUR AREA FROM LATE THURSDAY NIGHT THROUGH FRIDAY.

&&

.DISCUSSION...AS OF 10:30 AM PDT SUNDAY...OF NOTE...GOES CLOUD
THICKNESS IMAGERY NOW INDICATING STRATUS THICKNESS OVER 2000 FEET
NEAR POINT REYES INLAND TO AROUND SANTA ROSA AND MUCH OF SONOMA COUNTY.
THIS AREA AND THICKER CLOUD AREA FROM AROUND SANTA CRUZ AREA ALONG
COAST INTO SAN MATEO COUNTY WILL BE SLOWER TO CLEAR. REST OF
FORECAST AREA CLEARING BACK TO COAST FAIRLY QUICKLY AND SHOULD SEE
SUNSHINE BY MIDDAY. IMMEDIATE COASTAL AREAS WILL REMAIN MOSTLY
CLOUDY THRU BULK OF AFTERNOON GIVEN STRENGTH OF ONSHORE FLOW.
CURRENT FORECAST LOOKS ON TRACK WITH MORNING TEMPERATURES IN THE
50S CLIMBING TO THE 60S ALONG THE COAST TO 70S INLAND THIS
AFTERNOON.

ONSHORE FLOW TO CONTINUE NEXT FEW DAYS WITH EXTENSIVE PUSH OF
STRATUS INLAND NIGHTS AND MORNINGS. LATEST NAM STRENGTHENS ONSHORE
GRADIENT TO 3.7 MB SFO TO SAC MONDAY AFTERNOON. MONDAY MAY
ACTUALLY BE THE COOLEST DAY OF THE NEXT SEVERAL...THEN MARINE
LAYER MIXING INCREASES TOWARD MIDWEEK WITH UPPER LEVEL TROFING
DEVELOPING ALONG THE COAST AND COASTAL TEMPERATURES MAY WARM SLIGHTLY.

&&

.PREV DISCUSSION...AS OF 3:10 AM PDT SUNDAY...THE COOLING TREND
THAT BEGAN ON FRIDAY WILL CONTINUE TODAY...ALTHOUGH THE MAGNITUDE
OF TODAY`S COOLING IS EXPECTED TO BE LESS THAN WHAT OCCURRED
DURING THE PAST TWO DAYS.

A WEAK UPPER TROUGH CURRENTLY OFF THE WEST COAST IS FORECAST TO
SHIFT EASTWARD OVER THE CA COAST BY MONDAY MORNING. BOTH THE NAM
AND WRF MODELS INDICATE THIS WILL RESULT IN AN EVEN GREATER INLAND
SURGE OF MARINE LAYER CLOUDS TONIGHT...AS WELL AS CONTINUED COOL
CONDITIONS INTO MONDAY.

AFTER THE WEAK UPPER TROUGH MOVES INLAND ON MONDAY...SURFACE HIGH
PRESSURE WILL STRENGTHEN OFF THE NORTHERN CA COAST...RESULTING IN
INCREASING NORTHWEST WINDS ALONG THE COAST ON MONDAY NIGHT AND
TUESDAY. THESE WINDS SHOULD PRODUCE SUFFICIENT MIXING TO CLEAR OUT
MUCH OF THE LOW CLOUDINESS BY TUESDAY AFTERNOON AND THUS BRING
ABOUT SLIGHT WARMING ON TUESDAY.

AN UPPER LOW IS FORECAST TO DEVELOP OVER THE PAC NW BY MIDWEEK.
THE GFS AND ECMWF AGREE REASONABLY WELL IN DROPPING THAT LOW DUE
SOUTH ACROSS NORTHERN AND CENTRAL CALIFORNIA FROM LATE WEDNESDAY
NIGHT THROUGH THURSDAY NIGHT...AND THEN EJECTING THAT LOW
EASTWARD ON FRIDAY. BOTH MODELS ALSO FORECAST SCATTERED LIGHT
PRECIPITATION ACROSS PORTIONS OF OUR AREA FROM THURSDAY AFTERNOON
THROUGH LATE FRIDAY...WITH THE MOST WIDESPREAD SHOWER ACTIVITY
PROJECTED TO OCCUR ACROSS THE SOUTHERN PART OF OUR AREA LATE
THURSDAY NIGHT AND FRIDAY MORNING AS SHORTWAVE ROTATES INLAND OVER
THE CENTRAL COAST.

THE AIRMASS OVER OUR AREA WILL COOL SEVERAL DEGREES FROM LATE
WEDNESDAY INTO THURSDAY AS THE UPPER LOW DROPS IN FROM THE NORTH.
THIS COOLING WILL BE SUFFICIENT TO MIX OUT THE MARINE LAYER ACROSS
THE NORTHERN PART OF OUR AREA BY LATE WEDNESDAY AND IN ALL AREAS
BY THURSDAY. TEMPERATURES WILL COOL BELOW NORMAL IN ALL AREAS BY
THURSDAY AND REMAIN COOL THROUGH THE END OF THE WEEK.

THE UPPER LOW IS FORECAST TO MOVE WELL OFF TO OUR EAST BY LATE
FRIDAY...AND SHORTWAVE RIDGING IS EXPECTED TO PRODUCE DRY AND
SLIGHTLY WARMER WEATHER NEXT WEEKEND. BUT THE LONGER RANGE MODELS
MAINTAIN AN UNSETTLED PATTERN...WITH ANOTHER WEAK WEATHER SYSTEM
PROJECTED TO APPROACH CALIFORNIA EARLY NEXT WEEK.

&&

.AVIATION...AS OF 10:37 AM PDT SUNDAY...DEEP MARINE LAYER IN
PLACE WITH WIDESPREAD MVFR CIGS. KSJC AND KLVK HAVE CLEARED OUT
AND SFO IS SCT...BUT THE REMAINING TAF SITES SHOULD SEE ANOTHER HOUR OR
TWO OF MVFR BKN-OVC. CIGS RETURN AGAIN TONIGHT ALL LOCATIONS. CONF IS
MEDIUM-HIGH.

VICINITY OF KSFO...VFR EXPECTED THIS AFTERNOON WITH AN AFTERNOON
SEA BREEZE UP TO 16 KTS EXPECTED. MVFR CIGS EXPECTED BY 06Z.

SFO BRIDGE APPROACH...SIMILAR TO SFO.

MONTEREY BAY AREA TERMINALS...MVFR CIGS THROUGH 18-19Z. VFR THIS
AFTERNOON WITH AN EARLY RETURN OF MVFR CIGS.

&&

.BEACHES...AS OF 4:36 AM PDT SUNDAY...NO REAL CHANGE FROM PREVIOUS
FORECAST. A SERIES OF LONG PERIOD SOUTHERLY SWELLS WILL IMPACT THE
CENTRAL COAST TODAY. PT CONCEPTION BUOY IS ALREADY SHOWING 3.5 FT
AT 25 SECONDS. ALTHOUGH THE WAVE HEIGHTS ASSOCIATED WITH THESE
LONG PERIOD WAVES WILL BE RELATIVELY SMALL...4 TO 6 FEET...THE
POWERFUL NATURE OF LONG PERIOD WAVES WILL RESULT IN EXCEPTIONALLY
STRONG RIP CURRENTS ALONG THE COAST ESPECIALLY ON SOUTHERLY FACING
BEACHES SUCH AS STINSON BEACH IN MARIN COUNTY AND THE BEACHES
ALONG THE MONTEREY BAY COAST OF SANTA CRUZ COUNTY. ADDITIONALLY...THESE
LONG PERIOD WAVES WILL ALSO RESULT IN LARGE SHORE BREAK AT TWIN
LAKES STATE BEACH AND THE SANTA CRUZ BOARDWALK BEACH. LARGE SHORE
BREAK CAN RESULT IN NECK AND BACK INJURIES. IF YOU PLAN ON
ENTERING THE WATER PLEASE DO SO NEAR A LIFEGUARD AND ALWAYS KEEP
AN EYE ON THE OCEAN WHEN VISITING THE BEACH.

&&

.MARINE...AS OF 10:31 AM PDT SUNDAY...GUSTY NORTHERLY WINDS WILL
CONTINUE OVER THE NORTHERN OUTER WATERS THROUGH EARLY NEXT WEEK.
ELSEWHERE...SOUTHERLY FLOW WILL CONTINUE TODAY. NORTHERLY FLOW
WILL DEVELOP OVER MOST OF THE COASTAL WATERS TONIGHT AND MONDAY AS
HIGH PRESSURE BUILDS OVER THE REGION. A LONG PERIOD SOUTHERLY
SWELL WILL IMPACT THE COASTAL WATERS TODAY AND CONTINUE THROUGH
TUESDAY.

&&

.MTR WATCHES/WARNINGS/ADVISORIES...
     .TDAY...SCA...PT ARENA TO PT REYES 10-60 NM
             SCA...SF BAY NORTH OF THE BAY BRIDGE FROM 3 PM

&&

$$

PUBLIC FORECAST: KBB
AVIATION/MARINE: SIMS

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