121
FXUS66 KMTR 181201
AFDMTR
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SAN FRANCISCO CA
401 AM PST WED DEC 18 2024
..NEW AVIATION, MARINE
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.
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
(12Z TAFS)
ISSUED AT 357 AM PST WED DEC 18 2024
FICKLE FOG CONTINUES ACROSS THE BAY AREA WITH MOST SITES BOUNCING
FROM LIFR TO MVFR/VFR THROUGHOUT THE NIGHT. FOR MOST SITES, FOG WILL
CONTINUE TO CAUSE TEMPORARY REDUCTIONS IN CIGS/VIS THROUGH 16-18Z.
HIGHEST CONFIDENCE IS IN FOG IMPACTING SJC AND LVK WITH SLIGHTLY
LOWER CONFIDENCE FOR AIRPORTS ALONG THE SF BAY (SFO, OAK, APC).
CONDITIONS SHOULD IMPROVE BY LATE MORNING AS FOG COVERAGE
DIMINISHES. WINDS GENERALLY REMAIN LIGHT AND VARIABLE/OFFSHORE
THROUGH THE PERIOD. LOW TO MODERATE CONFIDENCE IN THE RETURN OF FOG
TOMORROW NIGHT. HIGHEST CONFIDENCE IS FOR SITES ACROSS THE NORTH BAY
AND EAST BAY, LOWEST CONFIDENCE FOR OAK/SFO/SJC. CURRENT THINKING IS
THAT VISIBILITIES WILL DIP SLIGHTLY ALONG THE BAY SHORELINE BUT
SHOULD REMAIN THE ATMOSPHERE SHOULD REMAIN DRY ENOUGH TO PREVENT
LIFR CONDITIONS FROM DEVELOPING. FOG IS NOT EXPECTED TO IMPACT MRY
OR SNS DURING THIS TAF PERIOD.
VICINITY OF SFO...PATCHY DENSE FOG CONTINUES TO IMPACT SFO WITH
VISIBILITIES DROPPING DOWN AS LOW AS 1/4SM. FOG IS CURRENTLY TEMPOED
THROUGH 16Z BUT MAY NEED TO BE EXTENDED THROUGH 18Z DEPENDING ON HOW
MUCH IT IS ABLE TO DEEPEN/EXPAND BY SUNRISE. VFR RETURNS DURING THE
AFTERNOON WITH LOW TO MODERATE CONFIDENCE THAT VIS WILL DROP AGAIN
OVERNIGHT. ENSEMBLE GUIDANCE IS CURRENTLY KEEPING VISIBILITIES IN
THE MVFR CATEGORY WITH HRRR GUIDANCE SHOWING DRIER OVERNIGHT
CONDITIONS THAN THE PAST FEW NIGHTS. WINDS REMAIN LIGHT AND
GENERALLY OFFSHORE BUT VARIABLE THROUGH THE TAF PERIOD.
SFO BRIDGE APPROACH...PATCHY FOG HAS DEVELOPED OVER THE SF BAY AND
IS IMPACTING PORTIONS OF THE SHORELINE. ENSEMBLE GUIDANCE SUGGESTS
THE BAY MAY CLEAR SLIGHTLY SLOWER (1-2 HOURS) THAN SFO WILL.
OTHERWISE SIMILAR TO SFO.
MONTEREY BAY TERMINALS...VFR THROUGH THE TAF PERIOD. LIGHT TO
MODERATE OFFSHORE, LOCALLY VARIABLE AT TIMES, CONTINUE THROUGH THE
TAF PERIOD. CONDITIONS LOOK TOO DRY IN THE MONTEREY BAY REGION TO
SUPPORT THE DEVELOPMENT OF FOG THROUGH 12Z TOMORROW. MODERATE SE
DRAINAGE WINDS LOOK TO DEVELOP AT SNS EARLY TOMORROW MORNING. MOS
GUIDANCE DOES SHOW SOME FOG DEVELOPING AT SNS AFTER 06Z THURSDAY BUT
CONFIDENCE REMAINS LOW AS MODERATE DRAINAGE WINDS SHOULD KEEP THE
ATMOSPHERE TOO TURBULENT FOR FOG TO FORM.
MARINE
(TODAY THROUGH MONDAY)
ISSUED AT 357 AM PST WED DEC 18 2024
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 145 PM PST TUE DEC 17 2024
A BEACH HAZARDS STATEMENT WAS ISSUED FOR 6 PM WEDNESDAY 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...BEACH HAZARDS STATEMENT FROM THIS EVENING THROUGH THURSDAY
AFTERNOON FOR CAZ006-505-509-529-530.
DENSE FOG ADVISORY UNTIL 9 AM PST THIS MORNING FOR CAZ502-503-
505-506-508-510-513.
PZ...NONE.
SHORT TERM...JM
LONG TERM....JM
AVIATION...KENNEDY
MARINE...KENNEDY
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