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

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FXUS66 KMTR 310620
AFDMTR

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SAN FRANCISCO BAY AREA
1020 PM PST FRI JAN 30 2015

.SYNOPSIS...DRY AND MILD CONDITIONS ARE EXPECTED TO CONTINUE
THROUGH THE MIDDLE OF NEXT WEEK WITH RAIN CHANCES CONFINED TO FAR
NORTHERN CALIFORNIA. TEMPERATURES WILL REMAIN SEVERAL DEGREES
ABOVE NORMAL. THERE ARE INDICATIONS THAT RAIN MAY MOVE INTO THE
AREA BY THE END OF NEXT WEEK.

&&

.DISCUSSION...AS OF 7:55 PM PST FRIDAY...AN UPPER LOW OVER
SOUTHERN CALIFORNIA PRODUCED ISOLATED THUNDERSTORMS OVER THE LA
BASIN TODAY. THIS LOW WAS TOO FAR REMOVED FROM OUR AREA TO HAVE
ANY IMPACT. THE DRY AND MILD WEATHER CONDITIONS THAT HAVE
PERSISTED FOR NEARLY THE ENTIRE MONTH OF JANUARY CONTINUED TODAY.
HIGHS TODAY WERE SEVERAL DEGREES WARMER THAN NORMAL AT MOST
LOCATIONS.

THE UPPER LOW OVER SOUTHERN CALIFORNIA WILL DRIFT TO THE SOUTHEAST
OVERNIGHT...ALLOWING AN UPPER RIDGE OFFSHORE ALONG 130W TO BUILD
INLAND ACROSS NORTHERN CA. AT THE SAME TIME...SURFACE HIGH
PRESSURE WILL QUICKLY BUILD TO OUR NORTH AND EAST OVER OREGON AND
NEVADA. THIS WILL RESULT IN THE DEVELOPMENT OF NORTH TO NORTHEAST
OFFSHORE WINDS IN THE HILLS OVERNIGHT...WITH WINDS EXPECTED TO
INCREASE AFTER MIDNIGHT. NORTHERLY WIND GUSTS UP TO 30 MPH ARE
LIKELY ACROSS THE RIDGES AND PEAKS LATE TONIGHT INTO SATURDAY
MORNING. THE STRONGEST WINDS WILL DEVELOP AFTER THE NOCTURNAL
INVERSION SETS UP TONIGHT AND SO MOST LOCATIONS NEAR SEA LEVEL
WILL CONTINUE TO SEE ONLY LIGHT WINDS. THE NORTHERLY WINDS WILL
BRING A DRIER AIRMASS INTO OUR REGION...WHICH WILL RESULT IN
CLEARING OF LOW CLOUDS THAT ARE PRESENTLY IN PLACE IN COASTAL
AREAS FROM SAN FRANCISCO SOUTH TO MONTEREY COUNTY. WOULD EXPECT
ALL LOW CLOUDS TO CLEAR BY MID MORNING ON SATURDAY. SURFACE
DEWPOINTS ARE STILL QUITE HIGH...AROUND 50 DEG F...AND ENOUGH OF
THIS LOW LEVEL MOISTURE WILL PROBABLY REMAIN TRAPPED IN THE
VALLEYS OVERNIGHT TO RESULT IN PATCHY LATE NIGHT AND EARLY MORNING
VALLEY FOG. LOOK FOR RAPID CLEARING OF THE FOG ON SATURDAY MORNING
ONCE THE INVERSION BREAKS AND DRY AIR ALOFT QUICKLY MIXES TO THE
SURFACE.

IN ADDITION TO DRY OFFSHORE FLOW...WE WILL SEE A WARMER AIRMASS
OVER OUR REGION TOMORROW AS 850 MB TEMPS INCREASE FROM ABOUT 9 DEG
C AT PRESENT TO ABOUT 14 DEG C BY SATURDAY AFTERNOON. THIS WILL
MEAN WARMER CONDITIONS TOMORROW...WITH A FEW LOCATIONS POSSIBLY
GETTING CLOSE TO RECORD DAILY HIGHS. MUCH WILL DEPEND ON HOW MUCH
OF THE DRIER AND WARMER AIRMASS ALOFT IS ABLE TO MIX DOWN INTO THE
BOUNDARY LAYER. IF THE WINDS ALOFT ARE NOT STRONG ENOUGH TO MIX
OUT THE COOL AND MOIST BOUNDARY LAYER AIR...WARMING WILL BE
LIMITED ACROSS MUCH OF THE SF BAY AREA WHICH WAS THE CASE LAST
WEEKEND. IT CURRENTLY LOOKS AS THOUGH OFFSHORE FLOW ON SATURDAY
MORNING WILL BE STRONGER COMPARED TO LAST WEEKEND AND SO WARMING
SHOULD OCCUR IN ALL AREAS TOMORROW.

THIS OFFSHORE WIND EVENT IS FORECAST TO BE SHORT-LIVED...WITH
OFFSHORE WINDS EXPECTED TO DECREASE IN THE HILLS BY SATURDAY NIGHT
AND LIGHT ONSHORE FLOW FORECAST TO REDEVELOP BY SUNDAY AFTERNOON.
THUS...IT LOOKS LIKE SATURDAY WILL BE THE WARMEST DAY OF THE
WEEKEND...WITH SLIGHT COOLING EXPECTED BY SUNDAY.

DRY WEATHER IS FORECAST TO CONTINUE THROUGH AT LEAST THE MIDDLE OF
NEXT WEEK AS OUR PERSISTENT UPPER RIDGE REMAINS LOCKED IN PLACE
ALONG THE WEST COAST. A SYSTEM MOVING OVER THE TOP OF THE RIDGE
AND INTO THE PAC NW ON MONDAY MAY GRAZE THE FAR NORTHERN EDGE OF
OUR AREA WITH SOME LIGHT WARM ADVECTION PRECIP ACCORDING TO THE
18Z GFS...BUT SUCH AN OUTCOME SEEMS UNLIKELY.

INDICATIONS ARE THAT WE WILL HAVE TO WAIT UNTIL NEAR THE END OF
NEXT WEEK TO SEE ANY REASONABLE CHANCE AT PRECIPITATION. THE GFS
AND ECMWF ARE IN AGREEMENT IN MOVING THE LONGWAVE RIDGE POSITION
FAR ENOUGH TO THE EAST TO ALLOW A LONGWAVE TROUGH AND ASSOCIATED
MOIST WSW FLOW OVER THE EASTERN PACIFIC TO REACH NORTHERN
CALIFORNIA BY THURSDAY NIGHT OR FRIDAY. INDIVIDUAL SHORTWAVE
TROUGHS RIDING ALONG THE MOIST WSWLY FLOW ARE THEN FORECAST TO
DELIVER SUBSTANTIAL RAINFALL TO PORTIONS OF NORTHERN CALIFORNIA
FROM THURSDAY NIGHT INTO THE WEEKEND OF FEB 7/8. HOWEVER...THE
MODELS DISAGREE ON HOW THAT RAINFALL WILL BE DISTRIBUTED. THE GFS
FOCUSES THE HEAVIEST PRECIP ACROSS NORTHWEST CA...GENERALLY NORTH
OF POINT ARENA...WITH AMOUNTS DROPPING OFF SIGNIFICANTLY SOUTH OF
THE GOLDEN GATE TO ALMOST NOTHING NEAR MONTEREY BAY. THE ECMWF
SPREADS PRECIP FARTHER TO THE SOUTH...WITH LESS IMPRESSIVE AMOUNTS
ACROSS NORTHWEST CA. OF COURSE...THIS IS STILL SIX TO NINE DAYS
INTO THE FUTURE AND CERTAINLY SUBJECT TO CHANGE. MUCH WILL DEPEND
ON WHETHER THE PERSISTENT RIDGE OVER CA WEAKENS SUFFICIENTLY TO
ALLOW FOR THE MOIST FLOW TO REACH OUR AREA. IF IT DOES...THIS
WOULD BE THE FIRST MEASURABLE RAIN MOST OF OUR AREA HAS SEEN IN
SIX WEEKS.

&&

.AVIATION...AS OF 9:55 PM PST FRIDAY...AREAS OF LOW CLOUDS CONTINUE
TO HANG ALONG THE IMMEDIATE COASTLINE WHILE SKIES ARE CLEAR INLAND.
WINDS ARE FORECAST TO GRADUALLY BECOME LIGHT OFFSHORE LATE TONIGHT
AND SATURDAY. VFR IS VERY LIKELY AREA-WIDE ON SATURDAY AS DRIER
CONDITIONS DEVELOP.

VICINITY OF KSFO...VFR. LIGHT WINDS.

KSFO BRIDGE APPROACH...SIMILAR TO KSFO.

MONTEREY BAY AREA TERMINALS...PARTIAL CLEARING OF LOW CLOUDS WILL
LIKELY SLOW WITH A RETURN TO LOW CLOUD DEVELOPMENT VERY LATE
TONIGHT. MVFR CIGS ARE FORECAST TO REDEVELOP BY 10Z. VFR RETURNS
BY LATE SATURDAY MORNING.

&

.MARINE...AS OF 10:18 PM PST FRIDAY...BASICALLY UNCHANGED FROM THE
DISCUSSION EARLIER TODAY: NORTH WINDS WILL GRADUALLY DECLINE
OVERNIGHT AND DROP BELOW SMALL CRAFT ADVISORY CRITERIA BY TOMORROW
MORNING. LIGHT NORTH WINDS WILL PREVAIL SUNDAY THROUGH EARLY NEXT
WEEK BEFORE VEERING TO THE SOUTH MIDWEEK. PATCHY DENSE FOG COULD
PERSIST IN THE NORTH BAY AND WEST DELTA AGAIN TOMORROW MORNING.

&&

.MTR WATCHES/WARNINGS/ADVISORIES...
     .TNGT...SCA...PT ARENA TO PT REYES 10-60 NM
             SCA...PT REYES TO PIGEON PT 10-60 NM
             SCA...PIGEON PT TO PT PINOS 10-60 NM
             SCA...PT PINOS TO PT PIEDRAS BLANCAS 10-60 NM

&&

$$

PUBLIC FORECAST: DYKEMA
AVIATION: CANEPA
MARINE: LARRY/CANEPA

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