264
FXUS66 KMTR 200514
AFDMTR
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SAN FRANCISCO CA
914 PM PST THU DEC 19 2024
..NEW UPDATE, AVIATION
SYNOPSIS
ISSUED AT 132 PM PST THU DEC 19 2024
DRY CONDITIONS CONTINUE THROUGH LATE FRIDAY, WITH AN ACTIVE WEATHER
PATTERN BRINGING SEVERAL ROUNDS OF RAIN INTO THE REGION. TWO PERIODS
OF LIGHT TO MODERATE RAIN ARE EXPECTED SATURDAY AND SUNDAY BEFORE
MORE INTENSE RAINFALL MONDAY AND TUESDAY, WITH ANOTHER POTENTIAL
IMPACTFUL SYSTEM DURING THE DAYS AFTER CHRISTMAS.
UPDATE
ISSUED AT 901 PM PST THU DEC 19 2024
NO MAJOR CHANGES TO THE FORECAST THIS MORNING. A LARGE SWATH OF
CIRRUS IS MOVING OVER THE REGION; HOWEVER, YOU CAN SEE SOME SNEAKY
STRATUS AND FOG BEING HIGHLIGHTED BELOW IT. GIVEN LAST NIGHT'S
FORECAST AND WINDS REMAINING ELEVATED AGAIN, OPTED TO NOT HOIST A
DENSE FOG ADVISORY FOR THE AREAS. SITES IN THE NAPA COUNTY AND
OTHER EAST BAY COUNTIES SHOW REDUCED VIS, BUT THEY HAVE ONLY
DROPPED TO 4 TO 6 MILES WHILE CARRYING CEILINGS OF A COUPLE
HUNDRED FEET IN THE METARS. WILL LET THE NIGHT SHIFT REASSESS THE
SITUATION AND HOIST THE DENSE FOG ADVISORY IF CONDITIONS LOOK
BETTER TONIGHT.
SHORT TERM
(THIS EVENING THROUGH FRIDAY)
ISSUED AT 132 PM PST THU DEC 19 2024
LOW STRATUS PERSISTS ACROSS THE NORTH BAY VALLEYS AND THE INTERIOR
EAST BAY, MAINLY WITHIN CONTRA COSTA COUNTY. SOME MIXING OUT IS
POSSIBLE THROUGH THE REST OF THE AFTERNOON. TONIGHT, WITH HIGH
CLOUDS COMING INTO THE PICTURE, THE FORECAST FOR FOG AND LOW STRATUS
IS LESS CONFIDENT, ALTHOUGH WIDESPREAD DENSE FOG IS NOT EXPECTED TO
DEVELOP.
TODAY MARKS THE END OF A WARMING TREND WITH HIGH TEMPERATURES
RANGING FROM THE MIDDLE 60S TO MIDDLE 70S IN THE INTERIOR VALLEYS OF
THE NORTH BAY AND CENTRAL COAST, CLOSER TO THE UPPER 50S TO THE
LOWER 60S ALONG THE COAST, THE BAYSHORE, AND THE INTERIOR EAST BAY
VALLEYS. FRIDAY MORNING'S LOWS REACH THE UPPER 30S TO THE MIDDLE 40S
IN THE INLAND VALLEYS AND THE MIDDLE 40S TO THE LOWER 50S NEAR THE
COAST. AS UPPER LEVEL RIDGING BEGINS TO GIVE WAY TO A MORE ACTIVE
PATTERN THROUGH FRIDAY, HIGHS WILL BEGIN TO DIP A FEW DEGREES IN THE
INTERIOR VALLEYS OF THE NORTH BAY AND CENTRAL COAST, WITH HIGHS
SIMILAR TO TODAY'S IN THE REST OF THE FORECAST REGION. SOME COASTAL
DRIZZLE IS POSSIBLE IN THE LATER HOURS OF FRIDAY, BUT THE FIRST
TASTE OF THE MULTIPLE WEATHER SYSTEMS THAT ARE EXPECTED FOR THE REST
OF THE 7-DAY FORECAST WON'T COME UNTIL LATE FRIDAY NIGHT IN THE
NORTH BAY.
FOR THOSE OF YOU PLANNING TO HEAD TO THE BEACH, BE AWARE: BUILDING
LONG PERIOD SWELL WILL RESULT IN AN INCREASED RISK FOR SNEAKER WAVES
THROUGH THE REST OF THE DAY, WITH A BEACH HAZARDS STATEMENT IN
EFFECT THROUGH 6 PM TODAY (SEE THE BEACHES SECTION FOR FURTHER
DETAILS).
LONG TERM
(FRIDAY NIGHT THROUGH NEXT WEDNESDAY)
ISSUED AT 132 PM PST THU DEC 19 2024
MULTIPLE ROUNDS OF RAIN BEGIN TO IMPACT THE WIDER BAY AREA AND
CENTRAL COAST LATE ON FRIDAY INTO SATURDAY WITH A SERIES OF
SHORTWAVES DURING THE WEEKEND. THE INITIAL ROUND OF RAIN THOSE TWO
DAYS WILL BRING AROUND 0.5-1" OF RAIN ACROSS THE NORTH BAY (LOCALLY
UP TO 1.5" IN THE HIGHER ELEVATIONS), AROUND 0.1-0.3" IN THE COASTAL
AND BAYSIDE BAY AREA, MONTEREY BAY REGION, AND SANTA LUCIAS, AND A
FEW SPRINKLES AT BEST IN THE INTERIOR EAST BAY, SANTA CLARA VALLEY,
AND THE INTERIOR CENTRAL COAST. IN ADDITION TO THE IMMEDIATE IMPACTS
OF THE RAINFALL, THIS SYSTEM WILL SET UP ANTECEDENT CONDITIONS FOR
FURTHER SYSTEMS TO CONTINUALLY INCREASE THE FLOODING RISK AS SOILS
SATURATE AND CREEKS FILL, ESPECIALLY ACROSS THE NORTH BAY. ANOTHER
ROUND OF RAIN ON SUNDAY WILL REINFORCE THE FLOODING CONCERNS WITH
FORECAST RAIN TOTALS FROM THIS SYSTEM QUITE SIMILAR TO THOSE FROM
SATURDAY'S SYSTEM. TO TOP IT ALL OFF, HIGH SURF WILL BEGIN TO IMPACT
THE COASTLINES, CREATING DANGEROUS CONDITIONS FOR INEXPERIENCED
SURFERS, INCLUDING LARGE BREAKING WAVES AND AN INCREASED RISK FOR
RIP CURRENTS (SEE THE BEACHES SECTION FOR FURTHER DETAILS).
BY LATE MONDAY AND TUESDAY, MORE SIGNIFICANT RAINFALL AND WIND
IMPACTS ARE EXPECTED ACROSS THE BAY AREA AND CENTRAL COAST WITH A
STRONGER LOW PRESSURE SYSTEM COMING INTO THE WESTERN UNITED STATES.
ALTHOUGH THE RAINFALL TOTALS ARE STILL BEING REFINED, THE CURRENT
MOST LIKELY SCENARIO SUGGESTS 1-3 INCHES OF RAIN FOR THE NORTH BAY
VALLEYS, UP TO 5" IN THE NORTH BAY MOUNTAINS, 1-2" IN THE COASTAL
RANGES AND NEAR SAN FRANCISCO AND OAKLAND, 0.5-1" IN THE INTERIOR
BAY AREA AND MONTEREY BAY REGION, AND 0.25-0.5" IN THE INTERIOR
CENTRAL COAST. WIND CONCERNS WILL ALSO RISE THAT DAY, WITH
PROBABILISTIC NBM GUIDANCE SUGGESTING A MODERATE TO BORDERLINE HIGH
CONFIDENCE (40-70% PROBABILITY) OF WIND GUSTS ABOVE 35 MPH ALONG THE
COAST; THROUGH GAPS, PASSES, AND VALLEYS; AND AT THE RIDGETOPS.
COMPLETING THE TRIFECTA OF HAZARDS WILL BE EVEN HIGHER SURF ALONG
THE PACIFIC COAST, AS SWELL WAVES REACH 20 FEET OR MORE IN THE OPEN
WATERS WITH PERIODS 20 SECONDS AND ABOVE. CONVECTIVE ACTIVITY CAN'T
BE RULED OUT EITHER WITH THE ECMWF SUGGESTING A PERIOD OF MUCAPE 200-
400 J/KG LATE MONDAY INTO TUESDAY, ALTHOUGH ANY SPECIFICS WILL
PROBABLY NEED TO WAIT A COUPLE OF DAYS FOR MORE GUIDANCE TO COME IN.
ENSEMBLE MODELS ARE CONVERGING ON ANOTHER ROUND OF RAINFALL,
POTENTIALLY SIGNIFICANT, INTO THE DAYS AFTER CHRISTMAS. CONFIDENCE
IN THE FORECAST FOR THAT SYSTEM REMAINS LOW. FOR THE 24 HOUR PERIOD
FROM CHRISTMAS AFTERNOON TO THURSDAY AFTERNOON, ENSEMBLE MODEL
CLUSTER ANALYSIS REVEALS A 50-60% PROBABILITY OF ANOTHER SIGNIFICANT
RAIN EVENT FOR THE NORTH BAY THAT DAY, AROUND A 30% PROBABILITY OF
LIGHTER RAINFALL TOTALS ACROSS THE REGION, AND A 10-20% CHANCE THAT
THE REGION REMAINS MOSTLY DRY. BY SATURDAY THE CHANCES FOR NO RAIN
RISE TO 40% WHILE THE CHANCES FOR SIGNIFICANT RAINFALL DROP TO 30%.
THEREFORE, IT'S WAY TOO EARLY TO START TALKING ABOUT SPECIFICS WITH
THIS SYSTEM, SO IT'S A GOOD IDEA TO KEEP TRACK OF FORECAST UPDATES
THROUGH THE WEEKEND AND THE EARLY PART OF NEXT WEEK AS THE IMPACTS
BECOME MORE CLEAR.
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
(TONIGHT THROUGH NEXT WEDNESDAY)
ISSUED AT 847 PM PST THU DEC 19 2024
DRY WEATHER CONTINUES THROUGH FRIDAY. AN ACTIVE WEATHER PATTERN
ACROSS THE PACIFIC WILL THEN BRING WET AND GUSTY WEATHER THIS
WEEKEND AND AGAIN EARLY NEXT WEEK. 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. GALE FORCE GUSTS COULD
BE POSSIBLE FOR SATURDAY.
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 3 AM TO 9 PM PST FRIDAY FOR PT ARENA
TO PT REYES 10-60 NM.
SHORT TERM...DIALH
LONG TERM....DIALH
AVIATION...KR
MARINE...KR
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