090
FXUS66 KMTR 201806
AFDMTR
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SAN FRANCISCO CA
1006 AM PST FRI DEC 20 2024
..NEW AVIATION, 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
(18Z TAFS)
ISSUED AT 947 AM PST FRI DEC 20 2024
LOW SUN ANGLE, LIGHT WINDS, COLDER OVERNIGHT, AMPLE LOW LEVEL
MOISTURE HAS LED TO IMPACTFUL FOG/LOW CIGS FOR THE BAY AREA THIS
MORNING, ESPECIALLY SFO/SJC. HIGH CLOUDS AND LIGHT WINDS HAS LED
TO A SLOW CLEARING/IMPROVEMENT. DO EXPECT SOME IMPROVEMENT BASED
ON TRENDS/GUIDANCE THROUGH 19Z. HOWEVER, GIVEN BROADER SATELLITE
PICTURE AND FLOW PATTERN WOULD NOT BE SURPRISED ONE BIT IF
PORTIONS OF THE N AND E BAY DIDN'T CLEAR MUCH OR AT ALL THROUGH
THE AFTERNOON. FOR TONIGHT, THE NEXT STORM APPROACHES FROM THE NW
LOWERING CIGS AND BRING -RA BACK TO THE REGION. SATURDAY AM RUSH
WILL BE IMPACTED WITH PRECIP AND LOWER CIGS. CONFIDENCE IS LOW TO
MEDIUM.
VICINITY OF SFO...NEAR TERM - CIGS THAT REDEVELOPED WILL LINGER
1830-19Z. SATELLITE DOES SHOW EDGE OF CLOUD DECK E OF THE
TERMINAL TRACKING WESTWARD. EXPECTING BETTER CONDITIONS THIS
AFTERNOON WITH VFR.
SFO BRIDGE APPROACH...SIMILAR TO SFO.
MONTEREY BAY TERMINALS...VFR. IFR CONDITIONS DEVELOP SATURDAY AM
WITH GUSTY SE WINDS AT SNS.
MARINE
(TODAY THROUGH WEDNESDAY)
ISSUED AT 947 AM PST FRI DEC 20 2024
A STORM SYSTEM OFF THE WILL BRING DETERIORATING CONDITIONS OVER
THE COASTAL WATERS FRIDAY INTO SATURDAY. THE STORM WILL BRING
RAIN, THUNDERSTORMS, INCREASING WINDS AND BUILDING SWELL.
OCCASIONAL GALE FORCE GUSTS NORTH OF POINT REYES 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 350 AM PST FRI DEC 20 2024
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
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 UNTIL 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...MM
MARINE...MM
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