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

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000
FXUS66 KMTR 211134
AFDMTR

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SAN FRANCISCO BAY AREA
434 AM PDT TUE OCT 21 2014

.SYNOPSIS...DRY WEATHER WITH SEASONABLE TEMPERATURES ARE EXPECTED
BOTH TODAY AND WEDNESDAY. THE NEXT STORM WILL BRING A CHANCE OF
RAIN TO THE NORTH BAY THURSDAY. ANOTHER SYSTEM WILL BRING A GOOD
CHANCE OF RAIN TO MOST OF THE DISTRICT FRIDAY OR SATURDAY.

&&

.DISCUSSION...AS OF 3:00 AM PDT TUESDAY...GENERALLY CLEAR START TO
THE DAY WITH FAIRLY LIGHT WINDS AND DRIER AIR HAS LEAD TO A COOLER
START. TEMPS HAVE DROPPED INTO THE 40S TO LOWER 50S IN MANY SPOTS
(WHICH IS 6 TO 12 DEGREES COOLER THAN MONDAY MORNING AT THIS TIME).
HIGHS ARE FORECAST TO BE CLOSE TO WHAT WE SAW YESTERDAY -- MID 60S
TO LOWER 70S IN MOST LOCATIONS. SIMILAR WEATHER IS FORECAST FOR
WEDNESDAY ALTHOUGH WITH A SLIGHT INCREASE IN 500 MB HEIGHTS, HIGHS
SHOULD WARM A FEW DEGREES.

BY THURSDAY A SHORTWAVE TROUGH ASSOCIATED WITH AN AREA OF LOW
PRESSURE OVER THE GULF OF ALASKA WILL APPROACH NORCAL. RAINFALL
WILL GENERALLY STAY TO THE NORTH OF OUR AREA, ALTHOUGH SOME RAIN
COULD MAKE IT DOWN INTO THE NORTH BAY ON THURSDAY. AMOUNTS SHOULD
BE LIGHT ALTHOUGH LOCALLY 1/3" IS POSSIBLE OVER THE NORTH BAY
MOUNTAINS. ALMOST ALL OF THE GUIDANCE HAS RAINFALL AMOUNTS
DROPPING OFF TO NEAR ZERO DOWN TO AROUND SAN FRANCISCO, SO
EXPECTATIONS ARE IT WILL BE VERY LIMITED IN AREA. WORTH NOTING
THAT THE GEM SOLUTION REMAINS THE MOST BULLISH WITH RAINFALL
AMOUNTS AND COVERAGE (EVEN BRINGING SOME DOWN TO MONTEREY BAY).
THIS IS A BIG OUTLIER FROM THE OTHER MODELS (INCLUDING HOW THE END
OF THE NAM IS TRENDING BY FRIDAY MORNING), SO WILL DISCOUNT IT FOR
NOW.

THINGS GET MORE INTERESTING FOR FRIDAY AND SATURDAY AS THE MAIN
COLD FRONT ASSOCIATED WITH THE LOW MOVES TO THE COAST. IT HAS BEEN
FUN TO WATCH THE EVOLUTION OF THE MODELS WITH THIS SYSTEM.
A FEW DAYS AGO, ALL INDICATIONS WERE THE RAIN WOULD STAY TO OUR
NORTH AND THE FRONT WOULD FALL APART NEAR OUR AREA. RUN AFTER RUN
HAS GOTTEN WETTER AND NOW ALL OF THE MAIN OPERATIONAL MODELS SHOW
A FAIRLY IMPRESSIVE BAND OF MOISTURE MOVING THROUGH OUR AREA
SOME TIME BETWEEN FRIDAY NIGHT AND SATURDAY. THE ECMWF WHICH HAD
BEEN THE DRIEST OF THE SOLUTIONS IS NOW NOTABLY WETTER THAN EVEN
JUST 24 HOURS AGO. IT BRINGS 1/3"-1/2" AROUND SF WITH LOCALLY MORE
THAN 2/3" OVER THE NORTH BAY. GFS IS SHOWING SIMILAR NUMBERS WHILE
THE GEM BRINGS 1-2" TO THE NORTH BAY WITH AROUND 1/2" TO SF AND
MONTEREY BAY. STILL A FEW DAYS OUT, SO WOULD LIKE TO SEE SOME OF
THE HIGHER RESOLUTION MODELS BEFORE ADVERTISING HEALTHY RAINFALL
AMOUNTS. HOWEVER, POPS WERE INCREASED DUE TO THE BETTER MODEL
AGREEMENT. WINDS COULD ALSO BE GUSTY AHEAD OF THE FRONT WITH 20-30
MPH POSSIBLE ESPECIALLY FOR SW FACING SPOTS NEAR THE COAST.

QUIET WEATHER RETURNS FOR SUNDAY THROUGH AT LEAST TUESDAY AS THE
STORM TRACK SHIFTS BACK TO THE NORTH.

&&

.AVIATION...AS OF 04:30 AM PDT TUESDAY...MOSTLY CLEAR SKIES THIS
MORNING IN THE WAKE OF THE COLD FRONT YESTERDAY. PATCHY HIGH
CLOUDS TO MOVE THROUGH LATER TODAY. LIGHT WINDS CONTINUE THROUGH
THE DAY. HIGH CONFIDENCE.

VICINITY OF KSFO...VFR THROUGH THE FORECAST PERIOD. MOSTLY LIGHT
WINDS THIS MORNING...INCREASING TO AROUND 15 KT OUT OF THE WEST IN
THE AFTERNOON.

KSFO BRIDGE APPROACH...SIMILAR AS KSFO.

MONTEREY BAY AREA TERMINALS...VFR. MOSTLY LIGHT WINDS...OFFSHORE
IN THE MORNING BEFORE SWITCHING ONSHORE IN THE AFTERNOON.

&&

.MARINE...AS OF 3:00 AM PDT TUESDAY...NORTHWEST WINDS OVER THE
COASTAL WATERS WILL INCREASE TODAY 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.

&&

.MTR WATCHES/WARNINGS/ADVISORIES...
     .TDAY...SCA...ROUGH BAR ADVISORY FOR SF BAR
             SCA...PT PINOS TO PT PIEDRAS BLANCAS 0-10 NM

&&

$$

PUBLIC FORECAST: BELL
AVIATION/MARINE: AC

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