464
FXUS66 KMTR 171843
AFDMTR
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SAN FRANCISCO CA
1033 AM PST TUE DEC 17 2024
..NEW AVIATION, MARINE
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
(18Z TAFS)
ISSUED AT 1033 AM PST TUE DEC 17 2024
LIFR-IFR CONDITIONS ARE SLOWLY IMPROVING THIS MORNING, OVERALL
CONDITIONS VARY FROM LIFR TO VFR, OTHERWISE CIRRUS CLOUDS ARE MOVING
EASTWARD THROUGH A MEDIUM 500 MB RIDGE OVER THE COASTAL WATERS.
A STABLE AIR MASS WILL PREVAIL DURING THE 18Z TAFS, ALONG WITH
LIGHT OFFSHORE WINDS EXCEPT LOCALLY VARIABLE AND ONSHORE DURING
THE MID TO LATE AFTERNOON, THEN LIGHT OFFSHORE TONIGHT AND
WEDNESDAY MORNING. LOWER TO MID LEVEL THERMAL RIDGING AND 500 MB
HEIGHT RIDGING WILL CONTINUE TO STEADILY DEVELOP OVER THE FORECAST
AREA TODAY, TONIGHT AND WEDNESDAY. RECENT SOAKING RAIN OVER MUCH
OF THE FORECAST AREA, LONG DECEMBER NIGHT-TIME RADIATIVE COOLING
AND LIGHT WINDS SUPPORT REDEVELOPMENT OF FOG TONIGHT AND WEDNESDAY
MORNING, THERE'S POTENTIAL FOR DENSE FOG REDEVELOPMENT AS WELL.
THINKING IS MOST RECENT HREF AND WRF FOR EXAMPLE ARE UNDER-FORECASTING
FOG IN OUR FORECAST AREA INCLUDING WITH RESPECT TO THE TAF SITES;
FOR 18Z HAVE INCLUDED LOWERING VISIBILITIES TO IFR WITH EVENING
ONSET OF FOG FOR KSTS, KAPC, KOAK AND KSFO. DENSE FOG MAY ALSO
DEVELOP AT KSJC, NOT YET INDICATED IN 18Z TAF RATHER ADVERTISING
IFR AT LEAST FOR THE MOMENT. NAM STATISTICAL GUIDANCE IS SHOWING
LOW SURFACE VISIBILITIES TONIGHT AND WEDNESDAY (AGAIN WEDNESDAY
NIGHT AND THURSDAY MORNING) FOR THE AFOREMENTIONED AIRPORT
LOCATIONS.
VICINITY OF SFO...IFR CEILING HOLDING STEADY PER RECENT SURFACE
OBSERVATIONS AND SATELLITE IMAGERY, LIFTING TO MVFR 19Z, ALLOWING
TO 23Z TO MIX OUT TO VFR; AN EAST WIND WITH WEAK OAK-SFO PRESSURE
GRADIENT IS CURRENTLY NOTED IN THE SURFACE OBSERVATIONS KEEPING
IFR FEED GOING FROM SF BAY. IT'S A NEAR PERSISTENCE FORECAST FOR
TONIGHT AND WEDNESDAY MORNING WHICH MEANS POTENTIAL FOR FOG
REDEVELOPMENT. SEEING LOW TO VERY LOW SURFACE VISIBILITY (CATEGORY
1, LESS THAN 1/2 MILE) IN THE NAM STATISTICAL GUIDANCE AS EARLY AS
06Z THIS EVENING, AND EXTENDING TO 15Z WEDNESDAY BEFORE SLOW CLEARING
TAKES PLACE. HEADS UP FOR WED NIGHT AND THU MORNING, SIMILAR WITH
FOG AND LOW VISIBILITY (PERSISTENCE). MAINLY LIGHT OFFSHORE WIND.
SFO BRIDGE APPROACH...SIMILAR TO SFO.
MONTEREY BAY TERMINALS...LIFR-IFR DUE LOW CEILINGS AND FOG SLOWLY
LIFTING, OTHERWISE IT'S VFR. VFR FOR THE AFTERNOON AND EARLY EVENING,
THEN AREAS LIFR-IFR REDEVELOPING TONIGHT AND WEDNESDAY MORNING. MAINLY
LIGHT OFFSHORE WIND.
MARINE
(TODAY THROUGH SUNDAY)
ISSUED AT 947 AM PST TUE DEC 17 2024
HIGH PRESSURE RETURNS TODAY WITH DRY WEATHER AND MAINLY LIGHT
OFFSHORE WINDS THROUGH THURSDAY NIGHT. LONG PERIOD 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 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 PIGEON PT
TO PT PINOS 0-10 NM-PT ARENA TO PT REYES 0-10 NM-PT ARENA
TO PT REYES 10-60 NM.
SMALL CRAFT ADVISORY UNTIL 3 AM PST WEDNESDAY FOR PIGEON PT TO
PT PINOS 10-60 NM-PT PINOS TO PT PIEDRAS BLANCAS 0-10 NM.
SHORT TERM...JM
LONG TERM....JM
AVIATION...CANEPA
MARINE...CANEPA
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