564
FXUS66 KMTR 171650
AFDMTR
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SAN FRANCISCO CA
850 AM PST TUE DEC 17 2024
..NEW UPDATE
SYNOPSIS
ISSUED AT 407 AM PST TUE DEC 17 2024
DENSE FOG OVERNIGHT WILL MAKE FOR A DIFFICULT COMMUTE AT TIMES
THIS MORNING, PLEASE DRIVE SLOWLY AND GIVE YOURSELF EXTRA TIME TO
REACH YOUR DESTINATION THROUGH THE MID-MORNING HOURS. AFTER THE
FOG LIFTS THIS MORNING, WE'LL SEE WARMER TEMPERATURES UNDER MOSTLY
SUNNY SKIES AND LIGHT WINDS ACROSS OUR ENTIRE AREA. AN UNSETTLED
PATTERN DEVELOPS LATER THIS WEEK, AND WILL PERSIST THROUGH THE
WEEKEND INTO NEXT WEEK.
UPDATE
ISSUED AT 844 AM PST TUE DEC 17 2024
WIDESPREAD STRATUS AND FOG ACROSS THE VALLEYS HAS BEEN SLOW TO MIX
OUT THIS MORNING. AS A RESULT, THE DENSE FOG ADVISORY CURRENTLY
IN EFFECT FOR MOST OF THE BAY AREA, THE MONTEREY BAY REGION, AND
THE NORTHERN SALINAS VALLEY HAS BEEN EXTENDED THROUGH 11 AM, WHICH
ALIGNS THE END TIME WITH THE DENSE FOG ADVISORY THAT OUR
NEIGHBORS IN SACRAMENTO HAVE ISSUED. WILL CONTINUE TO MONITOR
OBSERVATIONS IN CASE THE FOG DOES MIX OUT EARLIER THAN
ANTICIPATED. OTHERWISE, THE KEY FORECAST CONCERN WILL BE THE
ACTIVE WEATHER PATTERN THAT'S SET TO BEGIN THIS UPCOMING WEEKEND,
POTENTIALLY BEYOND THE CHRISTMAS PERIOD. THERE WILL BE A FULLER
DISCUSSION OF THIS POSSIBILITY WITH THE NEXT FORECAST UPDATE LATER
TODAY.
DIALH
SHORT TERM
(TODAY AND TONIGHT)
ISSUED AT 407 AM PST TUE DEC 17 2024
AS MENTIONED EARLIER IN THE EVENING UPDATE, DENSE FOG HAS DEVELOPED
ACROSS MUCH OF OUR AREA AND WILL CONTINUE FOR 2-3HRS PAST SUNRISE
THIS MORNING. A DENSE FOG ADVISORY REMAINS IN EFFECT THROUGH 9AM PST
FOR MUCH OF AREA. LOW AMPLITUDE, PROGRESSIVE RIDGING TODAY AND
TOMORROW WILL RESULT IN A PLEASANT INCREASE IN DAYTIME HIGHS OF
ABOUT 5 DEGREES FROM MONDAYS HIGH TEMPERATURES. BOUNDARY LAYER FLOW
WILL MOSTLY MAINTAIN AN OFFSHORE COMPONENT UNDER THE UPPER LEVEL
RIDGING THROUGH THE MIDDLE OF THE WEEK. WEDNESDAYS HIGHS FROM THE
EAST BAY SOUTH THROUGH THE REMAINDER OF THE INTERIOR CENTRAL COAST
WILL JUMP ABOUT ANOTHER 5 DEGREES TO AROUND 70 UNDER MOSTLY SUNNY
SKIES AND LIGHT WINDS.
LONG TERM
(WEDNESDAY THROUGH MONDAY)
ISSUED AT 407 AM PST TUE DEC 17 2024
THE OFFSHORE BOUNDARY LEVEL FLOW WILL PERSIST THROUGH THURSDAY
EVENING WITH HIGH TEMPERATURES IN THE 60S TO MID-70S ACROSS INTERIOR
VALLEYS. THURSDAY INTO FRIDAY A SHIFT IN THE PATTERN WILL RESULT IN
INCREASED SOUTHERLY FLOW UP TO 30KTS AT H85 FRIDAY MORNING INTO THE
AFTERNOON, AS H50 HEIGHTS BEGIN TO DROP OUT AHEAD OF A BROAD
DEEPENING TROUGH TO OUR WEST. THE FIRST OF TWO WAVES OF
PRECIPITATION WILL ARRIVE LATE FRIDAY NIGHT, BRUSHING THE THE NORTH
BAY WITH LIGHT RAIN, EXPECTED TO BE UNDER A TENTH OF AN INCH. THE
SECOND WAVE ASSOCIATED WITH THE TROUGH AXIS MOVING ONSHORE ACROSS
NORCAL AND SOUTHERN OREGON WILL BRING MORE IMPACTFUL RAINFALL, WITH
THE NORTH BAY NOW HIGHLIGHTED BY THE WPC IN THE DAY 5 EXCESSIVE RAIN
OUTLOOK FOR MODERATE TO HEAVY RAIN POSSIBLE SATURDAY AFTERNOON
THROUGH LATE SATURDAY NIGHT. THE ACTIVE LONGWAVE SYNOPTIC PATTERN
LOOKS TO CONTINUE THROUGH AND BEYOND THE EXTENDED FORECAST. GET OUT
ENJOY THE PLEASANT WEATHER THE NEXT FEW DAYS.
AVIATION
(12Z TAFS)
ISSUED AT 407 AM PST TUE DEC 17 2024
VERY FOGGY NIGHT WITH ALL AIRPORTS BOUNCING AROUND FROM LIFR TO MVFR
CONDITIONS. CURRENT THINKING IS THAT LOWERED VISIBILITIES AND FOG
WILL PREVAIL THROUGH 16-18Z BEFORE CONDITIONS IMPROVE TO VFR BUT
VISIBILITIES MAY FLUCTUATE AND SHOW TEMPORARY IMPROVEMENTS PRIOR TO
THEN. VFR CONDITIONS WILL RETURN BY LATE MORNING AND CONTINUE
THROUGH THE AFTERNOON/EVENING. CONFIDENCE IS SLIGHTLY LOWER IN
TONIGHT'S FOG POTENTIAL AS A DRIER AIR MASS ENTERS THE REGION.
CONFIDENCE IS HIGHEST THAT AT LEAST MVFR TO IFR CONDITIONS WILL
DEVELOP THROUGHOUT THE BAY AREA WHILE DRIER CONDITIONS ALONG THE
CENTRAL COAST LOOK TO KEEP MRY AND SNS VFR. WINDS GENERALLY STAY
LIGHT AND OFFSHORE THROUGH THE PERIOD WITH LOCALLY VARIABLE WINDS
POSSIBLE OVERNIGHT.
VICINITY OF SFO...MVFR WITH LIFR CONDITIONS POSSIBLE THROUGH THE
REST OF THE MORNING. FOG HAS BEEN CAUSING VISIBILITIES TO FLUCTUATE
THROUGHOUT THE MORNING AND IS EXPECTED TO LINGER THROUGH 16-18Z. FOG
COVERAGE SHOULD DISSIPATE THROUGH THE LATE MORNING HOURS WITH VFR
EXPECTED THROUGH THE AFTERNOON/EVENING. LOW TO MODERATE CONFIDENCE
THAT LOWER VISIBILITIES WILL RETURN TONIGHT WITH CURRENT TAF LEANING
TOWARDS MVFR CONDITIONS DEVELOPING OVERNIGHT. WINDS REMAIN LIGHT AND
GENERALLY OFFSHORE BEFORE BECOMING MORE NORTHWESTERLY TOWARDS THE
END OF THE TAF PERIOD.
SFO BRIDGE APPROACH...FOGGY CONDITIONS ACROSS THE SF BAY MAY CLEAR
OUT SLIGHTLY SLOWER THAN THE AIRPORT. OTHERWISE, SIMILAR TO SFO.
MONTEREY BAY TERMINALS...PATCHY DENSE FOG HAS DEVELOPED ACROSS THE
MONTEREY PENINSULA WITH VISIBILITIES AT MRY AND SNS FLUCTUATING
OVERNIGHT. PATCHY FOG WILL CONTINUE THROUGH 16/17Z WITH CONDITIONS
SET TO IMPROVE AND RETURN TO VFR AFTERWARDS. CONFIDENCE IS LOW THAT
FOG WILL DEVELOP AGAIN TONIGHT WITH CONDITIONS LOOKING TO BE DRIER
ACROSS THE CENTRAL COAST. WINDS GENERALLY REMAIN LIGHT AND OFFSHORE
THROUGH THE TAF PERIOD.
MARINE
(TODAY THROUGH SUNDAY)
ISSUED AT 407 AM PST TUE DEC 17 2024
PATCHY DENSE FOG IS POSSIBLE OVER THE COASTAL WATERS, PARTICULARLY
ALONG THE COASTLINE AND WITHIN THE SAN FRANCISCO BAY, THROUGH
EARLY TO MID TUESDAY MORNING. WHEN ENCOUNTERING DENSE FOG,
MARINERS MAY EXPERIENCE LIMITED VISIBILITY AND ARE ADVISED TO
SLOW DOWN. HIGH PRESSURE RETURNS TUESDAY WITH DRY WEATHER AND
LIGHT WINDS EXPECTED THROUGH FRIDAY. LONG PERIOD WESTERLY SWELL
WILL ARRIVE MIDWEEK WHICH MAY CAUSE INCREASED SHOALING ON HARBOR
ENTRANCES AND ELEVATED SNEAKER WAVE RISK ALONG THE COASTLINE.
ANOTHER LOW PRESSURE SYSTEM IS SET TO ARRIVE FRIDAY INTO THE
WEEKEND WHICH WILL RESULT IN ELEVATED WAVE HEIGHTS AND CREATE
HAZARDOUS CONDITIONS FOR SMALL CRAFTS.
BEACHES
ISSUED AT 437 AM PST TUE DEC 17 2024
A COMBINATION OF MODERATE PERIOD NORTHWESTERLY SWELL AND LONG PERIOD
WESTERLY SWELL WILL CONTRIBUTE TO ELEVATED POTENTIAL FOR SNEAKER
WAVE DEVELOPMENT EARLY WEDNESDAY MORNING THROUGH LATE THURSDAY
MORNING. THE COMBINATION OF NORTHWESTERLY AND WESTERLY SWELL WILL
LEAD TO ELEVATED CONCERNS ACROSS ALL COASTAL AREAS, INCLUDING
NORMALLY SHELTERED AREAS SUCH AS THE NORTHERN MONTEREY BAY. SNEAKER
WAVES ARE LIKELY TO BREAK BETWEEN 10 TO 13 FEET AND MAY POSE A RISK
TO ANY 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 HIGHER CONFIDENCE PERIOD OF ELEVATED SNEAKER WAVE
RISK IS LIKELY TO DEVELOP NEXT WEEKEND AS ANOTHER SYSTEM APPROACHES
THE WEST COAST.
MTR WATCHES/WARNINGS/ADVISORIES
CA...DENSE FOG ADVISORY UNTIL 11 AM PST THIS MORNING FOR CAZ006-
502>506-508>510-512-513-528>530.
PZ...SMALL CRAFT ADVISORY UNTIL 9 PM PST THIS EVENING FOR PT ARENA TO
PT REYES 0-10 NM-PT ARENA TO PT REYES 10-60 NM.
SMALL CRAFT ADVISORY UNTIL 9 PM PST THIS EVENING FOR PIGEON PT
TO PT PINOS 0-10 NM.
SMALL CRAFT ADVISORY UNTIL 3 AM PST WEDNESDAY FOR PT PINOS TO PT
PIEDRAS BLANCAS 0-10 NM.
SMALL CRAFT ADVISORY UNTIL 3 AM PST WEDNESDAY FOR PIGEON PT TO
PT PINOS 10-60 NM.
SHORT TERM...JM
LONG TERM....JM
AVIATION...KENNEDY
MARINE...KENNEDY
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