523
FXUS66 KMTR 181909
AFDMTR
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SAN FRANCISCO CA
1109 AM PST WED DEC 18 2024
..NEW AVIATION, BEACHES
SYNOPSIS
ISSUED AT 346 AM PST WED DEC 18 2024
ONCE THE FOG DISSIPATES THIS MORNING, WE'LL SEE MORE PLEASANT
WEATHER TODAY AND TOMORROW WITH ABOVE NORMAL TEMPERATURES, SUNNY
SKIES AND LIGHT WIND. LONG PERIOD SWELL BRINGS CHANCES FOR 'SNEAKER
WAVES' LATER TODAY THROUGH TOMORROW. UNSETTLED PATTERN SETS IN
FRIDAY BRINGING INCREASED CHANCES FOR RAIN AND WINDY CONDITIONS
THROUGH THE WEEKEND INTO THE BEGINNING OF NEXT WEEK.
UPDATE
ISSUED AT 822 AM PST WED DEC 18 2024
DENSE FOG CONTINUES TO IMPACT THE SF BAY REGION AND IS CAUSING
PROBLEMS AT THE SAN FRANCISCO AND SAN JOSE AIRPORTS. DUE TO
INCREASED CONFIDENCE IN EXTENDED IMPACTS DUE TO LIGHT WINDS AND
ADVECTIVE FOG FROM THE CENTRAL VALLEY, THE DENSE FOG ADVISORY
CURRENTLY IN EFFECT FOR MUCH OF THE BAY AREA HAS BEEN EXTENDED
THROUGH 11 AM. OTHERWISE, THE FOCUS ON THE OPERATIONS TEAM
CONTINUES TO BE ON THE SERIES OF RAIN SYSTEMS THAT'S SET TO START
NEXT WEEKEND. NO CHANGES TO THE FORECAST AT THIS TIME.
DIALH
SHORT TERM
(TODAY AND TONIGHT)
ISSUED AT 346 AM PST WED DEC 18 2024
PATCHY DENSE FOG TONIGHT IS NOT AS WIDESPREAD AS LAST NIGHT, HOWEVER
VISIBILITY DOWN TO A 1/4MI HAS PERSISTED ACROSS PORTIONS OF THE
SANTA CLARA VALLEY, NORTH THROUGH THE EAST BAY INTO THE NORTH BAY,
WITH THE ADVISORY SCHEDULED TO END AT 9 AM PST. ONCE THE FOG
DISSIPATES IT WILL BE A PLEASANT DAY ACROSS THE REGION WITH MOSTLY
SUNNY SKIES, LIGHT WINDS AND TEMPERATURES 5-10 DEGREES ABOVE NORMAL.
TOMORROW WILL BE SIMILAR, WITH EVEN SLIGHTLY WARMER TEMPERATURES,
ESPECIALLY ACROSS THE INTERIOR AND ELEVATED COASTAL RANGES AS LIGHT
OFFSHORE BOUNDARY LAYER FLOW WILL PERSIST THROUGH THE EVENING HOURS.
LATER TOMORROW NIGHT INTO FRIDAY, WE'LL SEE SOUTHERLY SURFACE FLOW
DEVELOP AND INCREASE OUT AHEAD OF THE FIRST OF NUMEROUS DISTURBANCES
TO IMPACT OUR AREA THROUGH THE EXTENDED. SEE THE BEACHES SECTION
BELOW FOR MORE INFORMATION ON THE BEACH HAZARD STATEMENT THAT GOES
INTO EFFECT THIS EVENING FOR POTENTIAL 'SNEAKER WAVES' FROM BUILDING
LONG PERIOD SWELL.
LONG TERM
(THURSDAY THROUGH TUESDAY)
ISSUED AT 346 AM PST WED DEC 18 2024
LATER TOMORROW NIGHT INTO FRIDAY, WE'LL SEE SOUTHERLY SURFACE FLOW
DEVELOP AND INCREASE OUT AHEAD OF THE FIRST OF NUMEROUS DISTURBANCES
TO IMPACT OUR AREA THROUGH THE EXTENDED FORECAST. PRECIPITATION
DURING THE DAY FRIDAY IS EXPECTED TO PRIMARILY STAY JUST OFFSHORE
BEFORE A SHORTWAVE TROUGH TRACKS ONSHORE FRIDAY AFTERNOON AND
EVENING BRINGING UP TO A 0.25" OF RAINFALL ACROSS THE NORTH BAY LATE
FRIDAY NIGHT. THE PRIMARY TROUGH TRACKS QUICKLY BEHIND THE SHORTWAVE
BY EARLY SATURDAY MORNING WITH STRONGER, DIFFLUENT H50 FLOW AROUND
80KTS SPREADING OVER OUR AREA BY LATE SATURDAY MORNING AND
AFTERNOON. SOUTHERLY SURFACE FLOW UP TO 25MPH BECOMES CONVERGENT
ACROSS THE BAY AREA SATURDAY AFTERNOON, WITH LIMITED BUT NONZERO
MUCAPE, POSSIBLY UP TO 100J/KG COINCIDING WITH THE TROUGH AXIS
PUSHING ONSHORE. LAPSE RATES ARE MOSTLY ANEMIC AND A LIMITING FACTOR
FOR MORE ROBUST CONVECTION, HOWEVER THERE IS A WINDOW SATURDAY
AFTERNOON WHERE LOW LEVEL LAPSE RATES STEEPEN SIGNIFICANTLY FROM THE
BAY AREA TO THE NORTH BAY COASTAL AREAS, CURRENTLY PEAKING IN THE 9-
9.5C/KM RANGE. HOW THE FORECAST FOR THESE LOW LEVEL LAPSE RATES
EVOLVE IN THE COMING DAYS WILL BE WATCHED CLOSELY. SUNDAY LOOKS TO
BE MOSTLY DRY BEFORE THE UNSETTLED PATTERN BRINGS THE NEXT WAVE OF
PRECIPITATION AND STRONG WIND. DETERMINISTIC GUIDANCE IS A BIT OUT
OF PHASE TEMPORALLY BUT HAS GOOD PATTERN CONSENSUS FOR A
POTENTIALLY STRONG AR DEVELOPING OFFSHORE MONDAY BRINGING
IMPACTFUL RAIN AND WIND AT SOME POINT ON TUESDAY ACROSS OUR ENTIRE
AREA.
AVIATION
(18Z TAFS)
ISSUED AT 1109 AM PST WED DEC 18 2024
AREAL COVERAGE OF VLIFR-IFR IN FOG AND DENSE FOG IS STARTING TO
SHOW SOME SIGNS OF SLOW IMPROVEMENT PER SATELLITE IMAGERY, SURFACE
OBSERVATIONS AND WEBCAMS, HOWEVER NOT ALL LOCATIONS ARE SHOWING
IMPROVEMENT AT THIS TIME. THE SOUTHERN SAN FRANCISCO BAY AND
SHORELINE TO THE SANTA CLARA VALLEY STILL HAS A FAIR AMOUNT OF FOG
TO MIX OUT, FOR EXAMPLE KSQL-KNUQ OBSERVATIONS ARE STILL AT OR LESS
THAN 1/4 MILE IN FOG. RECENT PILOT REPORTS OF ~ 500 FEET THICKNESS
FROM CLOUD TOP TO BASE, AND WITH AFTERNOON SUN SHOULD HELP STEADILY
IMPROVE CONDITIONS. FOG AND LOW CLOUDS ARE ALSO MAKING A LATE MORNING
RUN TO THE EAST BAY AND NORTH BAY ON EASTERLY WINDS THROUGH THE DELTA.
EXPECTING SLOW IMPROVEMENT IN GENERAL THROUGH THE AFTERNOON AND
EARLY EVENING, HOWEVER THE 18Z TAFS ARE PERSISTENCE FOR FOG AND
DENSE FOG RETURN TONIGHT AND THURSDAY MORNING BASED ON AIR MASS
STABILITY, NO CHANGE IN AIR MASS, LIGHT WINDS, LONG DECEMBER NIGHT-
TIME RADIATIVE COOLING HOURS (CIRRUS IS FORECAST THROUGH ABOUT LATE
EVENING OR MIDNIGHT TONIGHT THEN IT'LL BE MAINLY CLEAR TO CLEAR TO
THURSDAY MORNING). AREAS OF FOG AND DENSE FOG /VLIFR-IFR/ REDEVELOPING
TONIGHT AND THURSDAY MORNING
VICINITY OF SFO...A SMALL AREA OF FOG TO DENSE FOG IS HOVERING AROUND
THE SFO TERMINAL. FORECASTING VFR TO RETURN 20Z TODAY, LIGHT NORTHEAST
WIND CONTINUING THROUGH THE AFTERNOON PER STATISTICAL GUIDANCE. FOR
TONIGHT AND THURSDAY, PERSISTENCE FORECAST WITH FOG REDEVELOPING
BY 09Z TONIGHT/THURSDAY MORNING, MIXING OUT SIMILARLY APPROX 20Z
THURSDAY.
SFO BRIDGE APPROACH...THICKER FOG STILL COVERING THE APPROACH, OTHERWISE
EXPECTING A GRADUAL IMPROVEMENT TO VFR THROUGH THE AFTERNOON.
MONTEREY BAY TERMINALS...HIGH CONFIDENCE VFR FOR THE 18Z TAFS. LIGHT
AND VARIABLE WINDS TODAY, THEN EAST TO SOUTHEAST NEAR 5 KNOTS EXCEPT
INCREASING TO 10 TO 12 KNOTS IN THE SALINAS VALLEY TONIGHT AND THURSDAY
MORNING.
MARINE
(TODAY THROUGH MONDAY)
ISSUED AT 822 AM PST WED DEC 18 2024
DENSE FOG ACROSS THE SAN FRANCISCO BAY UNTIL 11 AM TODAY. LOCALLY
MODERATE WINDS ARE POSSIBLE ACROSS THE SOUTHERN COASTAL WATERS
THROUGH MID MORNING WITH LIGHT WINDS THEN EXPECTED TO THEN
CONTINUE THROUGH THURSDAY. MODERATE TO LONG PERIOD NORTHWESTERLY
TO WESTERLY SWELL WILL ARRIVE MIDWEEK CAUSING AN INCREASE IN
SHOALING ON HARBOR ENTRANCES AND ELEVATED SNEAKER WAVE RISK ALONG
THE COASTLINE. ANOTHER LOW PRESSURE SYSTEM ARRIVES FRIDAY INTO THE
WEEKEND BRINGING LIGHT TO MODERATE RAIN, FRESH TO STRONG WINDS,
AND ELEVATED WAVE HEIGHTS BETWEEN 15 TO 19 FEET. THIS WILL RESULT
IN DANGEROUS CONDITIONS FOR SMALL CRAFTS FRIDAY INTO THE WEEKEND.
BEACHES
ISSUED AT 1036 PM PST WED DEC 18 2024
A BEACH HAZARDS STATEMENT WILL BE IN EFFECT FROM 6 PM TODAY TO 6 PM
THURSDAY FROM SONOMA COUNTY TO MONTEREY COUNTY. MODERATE TO LONG
PERIOD NORTHWESTERLY SWELL WILL RESULT IN ELEVATED SNEAKER WAVE
DEVELOPMENT WITH SNEAKER WAVES LIKELY TO BREAK BETWEEN 10 AND 13
FEET. THE COMBINATION OF ELEVATED SNEAKER WAVE THREAT AND RIP
CURRENTS BOTH POSE A RISK TO BEACHGOERS WHO ARE CAUGHT UNAWARE.
VISITORS TO THE COAST MIDWEEK ARE ADVISED TO TAKE EXTRA CARE AND
NEVER TURN THEIR BACKS TO THE OCEAN AS SNEAKER WAVES MAY SWEEP
UNAWARE BEACHGOERS INTO THE OCEAN.
A SECOND PERIOD OF DANGEROUS, ELEVATED SURF NEAR 15 FEET WILL OCCUR
SATURDAY INTO SUNDAY AS ANOTHER SYSTEM APPROACHES THE WEST COAST.
THEN, A VERY LARGE AND POWERFUL, LONG PERIOD WEST SWELL TRAIN
WILL LIKELY ARRIVE ALONG OUR ENTIRE COASTLINE MONDAY INTO TUESDAY
NEXT WEEK. CURRENT GLOBAL WAVE MODELS ARE FORECASTING SWELL HEIGHTS
TO 20+ FEET WITH VERY ENERGETIC SWELL PERIODS OF 20+ SECONDS, THIS
WILL LEAD TO MUCH HIGHER BREAKERS INCLUDING LOCALIZED COASTAL FLOODING
IMPACTS. STAY TUNED FOR FURTHER UPDATES.
MTR WATCHES/WARNINGS/ADVISORIES
CA...DENSE FOG ADVISORY UNTIL 1 PM PST THIS AFTERNOON FOR CAZ006-506-
508-510-513.
BEACH HAZARDS STATEMENT FROM 6 PM PST THIS EVENING THROUGH
THURSDAY AFTERNOON FOR CAZ006-505-509-529-530.
PZ...DENSE FOG ADVISORY UNTIL 1 PM PST THIS AFTERNOON FOR SF BAY N OF
BAY BRIDGE.
SHORT TERM...JM
LONG TERM....JM
AVIATION...CANEPA
MARINE...CANEPA
VISIT US AT WWW.WEATHER.GOV/SANFRANCISCO
FOLLOW US ON FACEBOOK, TWITTER, AND YOUTUBE AT:
WWW.FACEBOOK.COM/NWSBAYAREA
WWW.TWITTER.COM/NWSBAYAREA
WWW.YOUTUBE.COM/NWSBAYAREA
CLICK HERE TO GO TO PREVIOUS BULLETINS.
Main Text Page