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

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FXUS66 KMTR 210026
AFDMTR

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SAN FRANCISCO BAY AREA
425 PM PST SAT DEC 20 2014

.SYNOPSIS...ISOLATED SHOWERS WILL POSSIBLE ACROSS OUR AREA
TONIGHT AND SLOWLY DIMINISH OVERNIGHT AS HIGH PRESSURE BUILDS OVER
THE EASTERN PACIFIC. KING TIDES WILL ARRIVE TO THE COAST ON SUNDAY
RESULTING IN COASTAL FLOODING ALONG THE IMMEDIATE COAST AND SAN
FRANCISCO BAY FRONT...INCLUDING COASTAL MARSHES AND SLOUGHS.

&&

.DISCUSSION...AS OF 2:39 PM SATURDAY...THE CURRENT SATELLITE WATER
VAPOUR IMAGE CONTINUES TO SHOW MOISTURE SPILLING OVER THE RIDGE
OF HIGH PRESSURE POSITIONED OVER THE EASTERN PACIFIC. KMUX DOPPLER
RADAR CONTINUES TO SHOW ISOLATED SHOWERS ASSOCIATED WITH THIS
MOISTURE PASSING OVER THE FORECAST AREA.

THE 1800Z GFS40 AND NAM12 HAVE INITIALIZED WELL WITH THE CURRENT
SYNOPTIC PATTERN. THE 1200Z ECMWF HAS ALSO INITIALIZED WELL AND ALL
3 MODELS REMAIN IN GOOD AGREEMENT THROUGH AT LEAST THE NEXT 84
HOURS. THE MODELS ALL SUGGEST THAT ISOLATED SHOWERS WILL STICK
AROUND THROUGH THIS EVENING WITH THE GREATEST IMPACT EXPECTED OVER
THE NORTH BAY AREA.

THE MODELS SLOWLY BUILD THE EAST PACIFIC RIDGE AND SLIDE IT
CLOSER TO THE COAST THROUGH THE WEEKEND. THIS WILL BRING AN END TO
THE SHOWERS BY SUNDAY AFTERNOON...DRY WEATHER IS THEN EXPECTED
THROUGH EARLY WEDNESDAY MORNING. THE GFS40 AND ECMWF CONTINUE TO
ADVERTISE A WEAK TROUGH OF LOW PRESSURE PUSHING INTO NORTHERN
CALIFORNIA WEDNESDAY. THIS WEAK TROUGH WILL BRING A POSSIBILITY OF
SHOWERS TO THE NORTH BAY AREA WEDNESDAY WITH SHOWERS POSSIBLE CHRISTMAS
EVE FOR THE REMAINDER OF THE FORECAST AREA. A SLIGHT CHANCE OF
SHOWERS WILL REMAIN A POSSIBILITY FOR THE NORTH BAY AREA ON
CHRISTMAS DAY. KEEP IN MIND THAT ANY IMPACT OF SHOWERS ON CHRISTMAS
DAY WILL BE MINIMAL .

&&

.AVIATION...AS OF 4:18 PM PST SATURDAY...A VERY HIGH WATER VAPOR
CONTENT AIR MASS FOR DEC COVERS ALMOST ALL OF CA THIS AFTERNOON.
TOTAL PRECIPITABLE WATERS AS OF THIS AFTERNOOON ARE >200% OF NORMAL
OVER MOST OF CA. THE WATER VAPOR IS RIDING NORTH AND EAST OVER A
BROAD RIDGE OF HIGH PRESSURE OVER THE EASTERN PACIFIC AND SETTLING
OVER THE WESTERN U.S.. THE UPPER LEVEL RIDGE WILL EXPAND OVER NORCAL
DURING THE PERIOD WHILE IN THE VERY NEAR TERM LOW LEVEL WARMER AIR
TRANSPORTED BY THE WIND PROVIDES NECCESARY LIFT FOR AREAS OF WET
WEATHER TO SPREAD SE. LOWEST CONFIDENCE IS IN THE FOG POTENTIAL
TONIGHT DUE TO MOIST AIR COMBINED WITH LONG NIGHT-TIME COOLING. LOW
TO MID LEVEL CLOUD COVER AS WELL AS RAINFALL MAY HELP SOMEWHAT TO
REDUCE AREAL COVERAGE OF FOG DURING THE PERIOD NONETHELESS WOULD
EXPECT AT LEAST LOCALIZED IFR IN CIGS/VSBYS OVERNIGHT.

VICINITY OF KSFO...LIGHT SOUTHEAST WINDS DUE TO PRESS GRADS SAC-SFO
0.9 MB AND SFO-HALF MOON BAY BUOY 0.6 MB. VFR/MVFR CIGS FORECAST
DURING THE PERIOD. LIGHT RAIN/WET RUNWAYS LIKELY BY 03Z THIS EVE.
LOW TO MODERATE CONFIDENCE.

KSFO BRIDGE APPROACH...SIMILAR TO KSFO.

MONTEREY BAY AREA TERMINALS...SIMILAR WEATHER SCENARIO TO THE BAY
AREA BUT DELAYED A BIT AS LIGHT RAIN BAND GRADUALLY SLIDES
SOUTHEAST THROUGH THE EVENING. VFR/MVFR CIGS FORECAST FOR THE
PERIOD. LIGHT RAIN TIMED TO REACH AREA BETWEEN 04Z-06Z. LIGHT
WINDS. LOW TO MODERATE CONFIDENCE.

&&

.MARINE...AS OF 2:11 PM PST SATURDAY...LARGE LONG PERIOD SWELLS WILL
BEGIN TO DIMINISH THROUGH THE AFTERNOON AND EVENING. LARGE BREAKING WAVES
WILL REMAIN A POSSIBILITY ACROSS THE SAN FRANCISCO BAR AND OFFSHORE REEFS
AND ROCK OUTCROPPINGS THROUGH THE REMAINDER OF THE DAY. HIGH PRESSURE WILL
BUILD OFF THE CALIFORNIA COAST TONIGHT INTO EARLY NEXT WEEK
RESULTING IN INCREASING NORTHWEST WINDS OVER THE SOUTHERN WATERS
BEGINNING SUNDAY. ADDITIONALLY... THE KING TIDES WILL IMPACT THE
COAST AND INLAND BAYS OVER THE NEXT THREE DAYS. KING TIDE IMPACTS
FOR SEAFARING VESSELS WILL OCCUR PRIMARILY DURING LOW TIDES...
WITH THE POSSIBILITIES OF BOAT KEELS TOUCHING HARBOR BOTTOM...
STRONG CURRENTS IN HARBOR ENTRANCES... AND ADDITIONAL BREAKING
WAVES OVER OFFSHORE REEFS.

&&

.MTR WATCHES/WARNINGS/ADVISORIES...
 .TNGT...HIGH SURF ADVISORY...THRU 10 PM FOR COASTAL SONOMA COUNTY TO
 MONTEREY COUNTY
 SCA...ROUGH BAR ADVISORY FOR SF BAR

&&

$$

PUBLIC FORECAST: LARRY
AVIATION: CANEPA
MARINE: DRP

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