061
FXUS66 KMTR 172145
AFDMTR
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SAN FRANCISCO CA
145 PM PST TUE DEC 17 2024
..NEW SYNOPSIS, SHORT TERM, LONG TERM, BEACHES
SYNOPSIS
ISSUED AT 127 PM PST TUE DEC 17 2024
DRY CONDITIONS CONTINUE THROUGH EARLY FRIDAY WITH POSSIBLE FOG AND
LOW STRATUS TONIGHT INTO WEDNESDAY MORNING. ACTIVE WEATHER PATTERN
BEGINS THIS UPCOMING WEEKEND WITH MULTIPLE ROUNDS OF IMPACTFUL RAIN
AND WIND POSSIBLE.
SHORT TERM
(TODAY AND TONIGHT)
ISSUED AT 127 PM PST TUE DEC 17 2024
LOW STRATUS CLOUDS ARE SLOWLY CONTINUING TO MIX OUT INTO THE
AFTERNOON, WITH SOME PATCHES OF CLOUD COVER, INCLUDING EASTERN SAN
JOSE AND AREAS NEAR LIVERMORE, PERSISTING THROUGH THE DAY. LIGHT
WINDS WILL PREVAIL THROUGH THE DAY WITH HIGH TEMPERATURES RANGING
FROM THE LOWER TO MIDDLE 60S IN THE INLAND VALLEYS, INTO THE MIDDLE
50S TO THE LOWER 60S ALONG THE COAST AND BAYSHORE. TONIGHT SEES
CHILLY TEMPERATURES, WITH LOWS REACHING THE UPPER 30S TO THE LOWER
40S IN THE INLAND VALLEYS AND THE MIDDLE 40S TO NEAR 50S NEAR THE
COAST, WITH THE POTENTIAL FOR A RETURN OF WIDESPREAD FOG AND LOW
STRATUS, ESPECIALLY ACROSS THE NORTH BAY AND THE NORTHERN BAY AREA.
THERE'S NOT ENOUGH CONFIDENCE TO ISSUE A DENSE FOG ADVISORY JUST
YET, BUT ONE MAY BE ISSUED LATER TODAY AS UPDATED MODEL GUIDANCE
COMES IN.
LONG TERM
(WEDNESDAY THROUGH MONDAY)
ISSUED AT 127 PM PST TUE DEC 17 2024
WITH AN UPPER LEVEL RIDGE STICKING AROUND THROUGH THE EARLY PART OF
FRIDAY, DRY CONDITIONS REMAIN ACROSS THE REGION THROUGH THE NEXT
COUPLE OF DAYS WITH THE INLAND VALLEYS REACHING HIGHS IN THE UPPER
60S TO LOWER 70S ON WEDNESDAY AND THURSDAY. BUILDING LONG PERIOD
SWELL WILL RESULT IN AN INCREASED RISK FOR SNEAKER WAVES LATE
WEDNESDAY INTO THURSDAY (SEE THE BEACHES SECTION FOR FURTHER
DETAILS).
LATER ON FRIDAY, THE PATTERN SHIFTS TO BRING MORE ACTIVE WEATHER
INTO THE REGION. ENSEMBLE MODEL GUIDANCE IS BEGINNING TO COALESCE ON
MULTIPLE ROUNDS OF IMPACTFUL RAIN AND WIND BEGINNING THIS WEEKEND
AND POTENTIALLY EXTENDING PAST CHRISTMAS DAY. THE INITIAL ROUND OF
RAIN LATE FRIDAY INTO SATURDAY WILL BRING AROUND 0.5-1.5" OF RAIN
ACROSS THE NORTH BAY AND LESS THAN 0.3" EVERYWHERE ELSE (ALTHOUGH
SOME ENSEMBLE MEMBERS SHOW RAINFALL TOTALS SIGNIFICANTLY HIGHER),
WITH TOTALS DECREASING THE FURTHER SOUTH YOU GO. THE WEATHER
PREDICTION CENTER HAS WENT AHEAD WITH A MARGINAL RISK OF EXCESSIVE
RAINFALL (AT LEAST A 5% CHANCE OF EXCEEDING FLASH FLOOD GUIDANCE)
ACROSS SONOMA COUNTY AND NEARBY PORTIONS OF NORTHERN MARIN AND
WESTERN NAPA COUNTIES. 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. BY CHRISTMAS EVE, THE CLIMATE PREDICTION CENTER IS
ALREADY SHOWING A MODERATE RISK (40-60% PROBABILITY) OF HEAVY
PRECIPITATION AND HIGH WINDS. THE RISK FOR HIGH WINDS EXTENDS INTO
THE DAYS AFTER CHRISTMAS, WHILE THE CPC OUTLOOK SUGGESTS TWO
DISTINCT DANGER PERIODS FOR HEAVY PRECIPITATION, ONE ON THE 24TH AND
ANOTHER FOR THE DAYS AFTER CHRISTMAS. IN ADDITION, HIGH SURF WILL
LEAD TO LOCALIZED COASTAL FLOODING IMPACTS (SEE THE BEACHES SECTION
FOR FURTHER DETAILS).
THIS PATTERN SHIFT IS SOMETHING THAT THE OPERATIONS TEAM WILL WATCH
CLOSELY FOR THE REST OF THIS WEEK, WITH PARTICULAR EMPHASIS ON ANY
MIGRATION OF THE HEAVIEST IMPACTS SOUTH OF THE NORTH BAY AND
POTENTIAL FOR HEAVILY IMPACTFUL RAINFALL TOTALS ACROSS THE HIGHER
ELEVATIONS. AS OF TODAY, THE NORTH BAY MOUNTAINS SEE A 30-40%
PROBABILITY OF 24-HOUR RAINFALL TOTALS OF 4 INCHES OR MORE ON
CHRISTMAS EVE, AND THE SANTA CRUZ MOUNTAINS SEE AROUND A 10% PERCENT
CHANCE OF THE SAME. ENJOY THIS NICE WEATHER WHILE YOU CAN, BUT ALSO
TAKE SOME TIME TO PREPARE FOR POTENTIAL FLOODING AND HEAVY WIND
CONCERNS.
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 145 PM PST TUE DEC 17 2024
A BEACH HAZARDS STATEMENT WAS ISSUED FOR 6 PM WEDNESDAY TO 6 PM
THURSDAY FROM SONOMA COUNTY TO MONTEREY COUNTY. MODERATE TO LONG
PERIOD NORTHWESTERLY SWELL WILL RESULT IN ELEVATED SNEAKER WAVE
DEVELOPMENT WITH SNEAKER WAVES LIKELY TO BREAK BETWEEN 10 AND 13
FEET. THIS ALONG WITH RIP CURRENTS BOTH POSE A RISK TO 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 PERIOD OF DANGEROUS, ELEVATED SURF NEAR 15 FEET WILL OCCUR
SATURDAY INTO SUNDAY AS ANOTHER SYSTEM APPROACHES THE WEST COAST.
THEN, A VERY LARGE AND POWERFUL, LONG PERIOD NORTHWEST 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...BEACH HAZARDS STATEMENT FROM WEDNESDAY EVENING THROUGH THURSDAY
AFTERNOON FOR CAZ006-505-509-529-530.
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...DIALH
LONG TERM....DIALH
AVIATION...CANEPA
MARINE...CANEPA
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