824
FXUS66 KMTR 201048
AFDMTR
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SAN FRANCISCO CA
248 AM PST FRI DEC 20 2024
..NEW SYNOPSIS, SHORT TERM, LONG TERM, MARINE
SYNOPSIS
ISSUED AT 234 AM PST FRI DEC 20 2024
A PARADE OF IMPACTFUL STORMS WILL IMPACT THE REGION LATE TONIGHT
THROUGH NEXT WEEK. LIFE-THREATENING BAY, OCEAN, AND BEACH CONDITIONS
BEGIN SATURDAY AND LINGER THROUGH NEXT WEEK.
SHORT TERM
(TODAY THROUGH SUNDAY)
ISSUED AT 234 AM PST FRI DEC 20 2024
TWO SHORTWAVE TROUGHS WILL TREK ACROSS THE REGION OVER THE WEEKEND
WITH THE FIRST SLATED FOR LATE FRIDAY NIGHT THROUGH SATURDAY AND THE
SECOND SLATED FOR SUNDAY. BOTH SYSTEMS WILL BE COMPARABLE IN TERMS
OF RAINFALL TOTALS WITH QPF NOT EXCEEDING 1.50" FOR EITHER OF THEM
AND RAINFALL TOTALS TAPERING OFF SIGNIFICANTLY FROM NORTH TO SOUTH.
SOUTHERLY WINDS WILL INCREASE AS THE SHORTWAVE TROUGHS MOVE ACROSS
THE AREA, BUT THEY WILL REMAIN BELOW WIND ADVISORY CRITERIA. WHILE
THESE TWO SYSTEMS ARE NOT LOOKING TO BE OVERLY IMPACTFUL IN AND OF
THEMSELVES, THEY WILL BE RESPONSIBLE FOR THE ANTECEDENT CONDITIONS
GOING INTO THE MORE IMPACTFUL SYSTEMS NEXT WEEK. AS SOILS APPROACH
SATURATION IT IS MORE LIKELY THAT TREES WILL FALL, MUD AND ROCK WILL
SLIDE, AND CREEKS AND STREAMS WILL RISE. SPC HAS HIGHLIGHTED MOST OF
MARIN AND SONOMA COUNTIES FOR GENERAL OR NON-SEVERE THUNDERSTORMS
BETWEEN 4 AM SATURDAY AND 4 AM SUNDAY. A HIGH SURF ADVISORY WILL GO
INTO EFFECT AT 6 AM SATURDAY AND RUN THROUGH 4 PM SUNDAY WITH
LIFE-THREATENING BAY, OCEAN, AND BEACH CONDITIONS LINGERING INTO
NEXT WEEK. IF YOU WANT TO SEE LARGE BREAKING WAVES, THERE'S AN APP
FOR THAT (SURFLINE), DO NOT GO TO THE BEACH.
LONG TERM
(MONDAY THROUGH THURSDAY)
ISSUED AT 234 AM PST FRI DEC 20 2024
MONDAY THROUGH THURSDAY WILL BE THE MOST CRITICAL TIME PERIOD AS
TWO MORE SHORTWAVE TROUGHS PLOW THROUGH THE REGION, THE FIRST
SLATED FOR MONDAY MORNING THROUGH TUESDAY MORNING AND THE SECOND
SLATED FOR WEDNESDAY AFTERNOON THROUGH THURSDAY. BOTH OF THESE
SYSTEMS WILL BRING WIDESPREAD IMPACTFUL RAINFALL WITH RAINFALL
TOTALS AS HIGH AS 2.50" WITH THE MONDAY-TUESDAY SYSTEM AND UP TO
3.50" WITH THE WEDNESDAY-FRIDAY SYSTEM. WPC HAS HIGHLIGHTED MARIN,
NAPA, AND SONOMA COUNTIES FOR A MARGINAL OR AT LEAST 5% RISK OF
RAINFALL EXCEEDING FLASH FLOOD GUIDANCE BETWEEN 4 AM MONDAY AND 4
AM TUESDAY. AS THE RIVERS RISE SO DO FLOODING CONCERNS WITH
DETERMINISTIC FORECASTS SHOWING A RAPID RISE BEGINNING MONDAY
NIGHT. THE GREATEST CHANCE FOR CONVECTION IS WITH THE MONDAY
MORNING-TUESDAY MORNING SYSTEM WITH CHANCES FOR THUNDERSTORMS UP
TO 20%. THERE IS UP TO A 30% CHANCE IN REACHING WIND ADVISORY
CRITERIA (WIND GUSTS 45+ MPH) WITH THESE SYSTEMS. LIFE-THREATENING
BAY, OCEAN, AND BEACH CONDITIONS WILL RETURN MONDAY AND CONTINUE
THROUGH NEXT WEEK WITH A HIGH SURF WARNING LIKELY NEEDED DURING
THIS TIME FRAME.
BELOW ARE MAINSTEM FORECAST POINTS AND THE ENSEMBLE FORECAST OF
EXCEEDING (ACTION/MONITOR STAGE), (MINOR FLOOD STAGE) BETWEEN MONDAY
AND NEXT SUNDAY.
SONOMA COUNTY:
RUSSIAN RIVER - GUERNEVILLE (GUEC1): 39%, 34%
RUSSIAN RIVER - HEALDSBURG (HEAC1): 11%, N/A
NAPA COUNTY:
NAPA RIVER - ST. HELENA (SHEC1): 43%, 20%
NAPA RIVER - NAPA (APCC1): 30%, 11%
SANTA CLARA COUNTY:
GUADALUPE RIVER - SAN JOSE AT ALMADEN EXPRESSWAY (GUDC1): <2%, <2%
SANTA CRUZ COUNTY:
SAN LORENZO RIVER - BIG TREES (BTEC1): 5%, N/A
MONTEREY COUNTY:
CARMEL RIVER - ROBLES DEL RIO (RDRC1): <2%, <2%
AVIATION
(06Z TAFS)
ISSUED AT 901 PM PST THU DEC 19 2024
SATELLITE IMAGERY SHOWS HIGH CLOUD FLOWING OVER THE BAY AREA WITH
THESE CLOUDS GRADUALLY COVERING THE CENTRAL COAST. UNDERNEATH
THESE CLOUDS LURKS STRATUS AND FOG FOR AREAS IN THE NORTH AND
EAST BAY. CONFIDENCE IS LOW FOR WIDESPREAD LIFR FOG, WITH KSTS
LIKELY BEING THE MAIN CONTENDER. ELSEWHERE MVFR TO IFR VIS IS
POSSIBLE IF WINDS EASE, BUT SHOULD THE NOT LOOK FOR IFR OR PERHAPS
LIFR CEILINGS. WINDS STAY LIGHT TO MODERATE THROUGH THE TAF
PERIOD. AS THE NEXT RAIN SYSTEM APPROACHES, WINDS ALOFT INCREASE
LEADING TO LLWS CONCERNS INTO FRIDAY NIGHT, WITH LIGHT RAIN
FOLLOWING. IT'S TOO EARLY, DUE TO CONFIDENCE BEING TOO LOW, TO
ADD THUNDER TO THE TAFS, BUT WE'LL NEED TO BE MINDFUL OF THAT FOR
AT LEAST OUR NORTH BAY COUNTIES.
VICINITY OF SFO...VRF SHOULD LAST THROUGH THE LATE NIGHT BEFORE
MIST AND FOG BEGIN TO AFFECT THE SF BAY. MIST/FOG FILLS OVER SFO
INTO EARLY FRIDAY AND LASTS THROUGH THE LATE MORNING. WINDS STAY
LIGHT AND VARIABLE UNTIL FRIDAY AFTERNOON, BEFORE MORE MODERATE
EASTERLY WINDS ARRIVE. WINDS TURN SOUTHERLY INTO THAT NIGHT AS
SHOWERS APPROACH, WITH SOME CONCERNS FOR LLWS AS STRONG
SOUTHEASTERLY WINDS DEVELOP ALOFT.
SFO BRIDGE APPROACH...SIMILAR TO SFO.
MONTEREY BAY TERMINALS...VFR CONDITIONS LASTS INTO THE EARLY
MORNING HOURS, WITH LOWERING CEILINGS BEING POSSIBLE NEAR
DAYBREAK. MOST GUIDANCE SUGGEST MVFR CIGS WITH THIS AND THE
CLEARING OUT BY THE AFTERNOON, BUT THERE IS A SMALL CHANCE WE
COULD GO IFR. CONFIDENCE IS TOO LOW TO ADD IT BUT SOME MODELS HAVE
HINTED AT IT. IN TERMS OF WINDS, AROUND MRY THEY STAY LIGHT AND
VARIABLE THROUGH THE TAF PERIOD. WINDS FOR SNS STAY RELATIVELY
LIGHT UNTIL SOUTHEASTERLY DRAINAGE WINDS BUILD OVERNIGHT.
MARINE
(TODAY THROUGH WEDNESDAY)
ISSUED AT 234 AM PST FRI DEC 20 2024
DRY WEATHER CONTINUES THROUGH FRIDAY BEFORE AN ACTIVE WEATHER
PATTERN DEVELOPS ACROSS THE PACIFIC BRINGING RAIN AND GUSTY WINDS
THIS WEEKEND AND AGAIN EARLY NEXT WEEK. GALE FORCE GUSTS COULD BE
POSSIBLE ACROSS THE NORTHERN WATERS ON SATURDAY. WAVE HEIGHTS
WILL REMAIN ELEVATED THROUGH LATE NEXT WEEK WITH 15 TO 20 FEET
WAVES MONDAY THROUGH WEDNESDAY. PERSISTENT DANGEROUS CONDITIONS
FOR SMALL CRAFTS ARE EXPECTED FRIDAY INTO NEXT WEEK.
BEACHES
ISSUED AT 132 PM PST THU DEC 19 2024
A BEACH HAZARDS STATEMENT REMAINS IN EFFECT THROUGH 6 PM TODAY
FROM SONOMA COUNTY TO MONTEREY COUNTY. MODERATE TO LONG PERIOD
NORTHWESTERLY SWELL WILL RESULT IN ELEVATED SNEAKER WAVES 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 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 OF 15 TO 18 FEET, WITH
OCCASIONAL BREAKERS UP TO 20 FEET, WILL OCCUR SATURDAY MORNING TO
SUNDAY AFTERNOON AS ANOTHER SYSTEM APPROACHES THE WEST COAST,
WITH A HIGH SURF ADVISORY NEWLY ISSUED FOR THE PACIFIC COAST FROM
6 AM SATURDAY THROUGH 4 PM SUNDAY.
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...HIGH SURF ADVISORY FROM 6 AM SATURDAY TO 4 PM PST SUNDAY FOR
CAZ006-505-509-529-530.
PZ...SMALL CRAFT ADVISORY FROM 9 AM THIS MORNING TO 3 PM PST SATURDAY
FOR PT ARENA TO PT REYES 0-10 NM-PT ARENA TO PT REYES 10-60
NM.
SMALL CRAFT ADVISORY FROM 9 PM THIS EVENING TO 3 PM PST SATURDAY
FOR PIGEON PT TO PT PINOS 0-10 NM-PIGEON PT TO PT PINOS 10-
60 NM-PT REYES TO PIGEON PT 0-10 NM.
SMALL CRAFT ADVISORY FROM 3 PM THIS AFTERNOON TO 3 PM PST
SATURDAY FOR PT PINOS TO PT PIEDRAS BLANCAS 0-10 NM.
SHORT TERM...SARMENT
LONG TERM....SARMENT
AVIATION...KR
MARINE...RGASS
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