852
FXUS66 KMTR 182149
AFDMTR
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SAN FRANCISCO CA
149 PM PST WED DEC 18 2024
..NEW SYNOPSIS, SHORT TERM, LONG TERM
SYNOPSIS
ISSUED AT 148 PM PST WED DEC 18 2024
FOG AND LOW STRATUS ARE SLOWLY MIXING OUT ACROSS THE BAY AREA AND
WILL LIKELY RETURN TONIGHT. ACTIVE WEATHER PATTERN BEGINS THIS
UPCOMING WEEKEND WITH MULTIPLE ROUNDS OF IMPACTFUL RAIN AND WIND
POSSIBLE.
SHORT TERM
(THIS EVENING THROUGH THURSDAY)
ISSUED AT 148 PM PST WED DEC 18 2024
FOG AND LOW STRATUS PERSISTS ACROSS EASTERN MARIN COUNTY AND ACROSS
THE INTERIOR EAST BAY. THE HIGHER SUN ANGLE IS BEGINNING TO MIX OUT
THE COASTAL AND BAYSIDE FOG, BUT WITH A ROBUST CLOUD DECK OVER THE
CENTRAL VALLEY, PORTIONS OF THE INTERIOR EAST BAY COULD REMAIN
SOCKED IN THROUGH THE REST OF THE DAY. TONIGHT, EXPECT A RETURN OF
DENSE FOG THROUGHOUT THE BAY AREA AND NORTH BAY VALLEYS, AND A
RENEWED DENSE FOG ADVISORY FOR THE REGION IS HIGHLY LIKELY.
OTHERWISE, A WARMING TREND CONTINUES TODAY INTO THURSDAY WITH HIGH
TEMPERATURES RANGING FROM THE MIDDLE 60S TO LOWER 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. THURSDAY 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, WITH HIGH TEMPERATURES SIMILAR OR
SLIGHTLY WARMER TO TODAY. 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 LATE TONIGHT INTO TOMORROW (SEE THE
BEACHES SECTION FOR FURTHER DETAILS).
LONG TERM
(THURSDAY NIGHT THROUGH NEXT TUESDAY)
ISSUED AT 148 PM PST WED DEC 18 2024
THE UPPER AIR PATTERN SHIFTS LATE ON FRIDAY INTO SATURDAY, AS THE
UPPER LEVEL RIDGE THAT'S BRINGING US THE WARMER TEMPERATURES MOVES
OFF TO THE EAST AND ALLOWS FOR A SERIES OF STORM SYSTEMS TO COME
INTO THE WESTERN UNITED STATES. THE INITIAL ROUND OF RAIN LATE
FRIDAY INTO SATURDAY WILL BRING AROUND 0.5-1.5" OF RAIN ACROSS THE
NORTH BAY, AROUND 0.1-0.3" IN THE BAY AREA, MONTEREY BAY REGION, AND
SANTA LUCIAS, AND A FEW SPRINKLES AT BEST IN THE INTERIOR CENTRAL
COAST. AROUND A 25-35% PROBABILITY REMAINS OF RAINFALL TOTALS ABOVE
2 INCHES ACROSS THE SONOMA COASTAL RANGES AND THE MAYACAMAS. THE
WEATHER PREDICTION CENTER IS MAINTAINING A MARGINAL RISK OF
EXCESSIVE RAINFALL (AT LEAST A 5% CHANCE OF EXCEEDING FLASH FLOOD
GUIDANCE) ON SATURDAY 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, ESPECIALLY
ACROSS THE NORTH BAY. THIS IS FURTHER REINFORCED BY ANOTHER ROUND OF
RAIN ON SUNDAY, WITH 0.25-0.75" IN THE NORTH BAY (LOCALLY UP TO 1"
IN THE MOUNTAINS) AND UP TO 0.25" IN THE BAY AREA. THERE IS ALSO A
LOW, BUT NONZERO, CHANCE FOR LOW TOPPED CONVECTION ON SATURDAY ALONG
THE COAST, ALTHOUGH DETAILS ARE VERY FUZZY AT THIS TIME. AS FOR ANY
CHANCE OF SEVERE THUNDERSTORMS, THAT'S PROBABLY NOT GOING TO GET
MUCH CLEARER FOR ONE OR TWO MORE DAYS.
BY MONDAY AND TUESDAY, MORE SIGNIFICANT RAINFALL AND WIND IMPACTS
ARE EXPECTED ACROSS THE BAY AREA AND CENTRAL COAST. 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, 0.5-1"
IN THE BAY AREA AND MONTEREY BAY REGION, AND 0.25-0.5" IN THE
INTERIOR CENTRAL COAST. IN ADDITION, HIGH SURF WILL LEAD TO
LOCALIZED COASTAL FLOODING IMPACTS (SEE THE BEACHES SECTION FOR
FURTHER DETAILS).
ENSEMBLE MODELS ARE CONVERGING ON ANOTHER ROUND OF RAINFALL,
POTENTIALLY SIGNIFICANT, INTO THE DAYS AFTER CHRISTMAS. EARLY
SIGNALS FROM THE ENSEMBLE MODELS SUGGEST THAT A RIDGING PATTERN
COULD SET UP FOR THE LAST FEW DAYS OF THE YEAR, BUT WITH THE NEW
YEAR'S HOLIDAY SO FAR OUT, THERE'S VERY LOW CONFIDENCE IN THAT RIGHT
NOW.
AVIATION
(18Z TAFS)
ISSUED AT 1109 AM PST WED DEC 18 2024
AREAL COVERAGE OF VLIFR-IFR IN FOG AND DENSE FOG IS STARTING TO
SHOW SOME SIGNS OF SLOW IMPROVEMENT PER SATELLITE IMAGERY, SURFACE
OBSERVATIONS AND WEBCAMS, HOWEVER NOT ALL LOCATIONS ARE SHOWING
IMPROVEMENT AT THIS TIME. THE SOUTHERN SAN FRANCISCO BAY AND
SHORELINE TO THE SANTA CLARA VALLEY STILL HAS A FAIR AMOUNT OF FOG
TO MIX OUT, FOR EXAMPLE KSQL-KNUQ OBSERVATIONS ARE STILL AT OR LESS
THAN 1/4 MILE IN FOG. RECENT PILOT REPORTS OF ~ 500 FEET THICKNESS
FROM CLOUD TOP TO BASE, AND WITH AFTERNOON SUN SHOULD HELP STEADILY
IMPROVE CONDITIONS. FOG AND LOW CLOUDS ARE ALSO MAKING A LATE MORNING
RUN TO THE EAST BAY AND NORTH BAY ON EASTERLY WINDS THROUGH THE DELTA.
EXPECTING SLOW IMPROVEMENT IN GENERAL THROUGH THE AFTERNOON AND
EARLY EVENING, HOWEVER THE 18Z TAFS ARE PERSISTENCE FOR FOG AND
DENSE FOG RETURN TONIGHT AND THURSDAY MORNING BASED ON AIR MASS
STABILITY, NO CHANGE IN AIR MASS, LIGHT WINDS, LONG DECEMBER NIGHT-
TIME RADIATIVE COOLING HOURS (CIRRUS IS FORECAST THROUGH ABOUT LATE
EVENING OR MIDNIGHT TONIGHT THEN IT'LL BE MAINLY CLEAR TO CLEAR TO
THURSDAY MORNING). AREAS OF FOG AND DENSE FOG /VLIFR-IFR/ REDEVELOPING
TONIGHT AND THURSDAY MORNING
VICINITY OF SFO...A SMALL AREA OF FOG TO DENSE FOG IS HOVERING AROUND
THE SFO TERMINAL. FORECASTING VFR TO RETURN 20Z TODAY, LIGHT NORTHEAST
WIND CONTINUING THROUGH THE AFTERNOON PER STATISTICAL GUIDANCE. FOR
TONIGHT AND THURSDAY, PERSISTENCE FORECAST WITH FOG REDEVELOPING
BY 09Z TONIGHT/THURSDAY MORNING, MIXING OUT SIMILARLY APPROX 20Z
THURSDAY.
SFO BRIDGE APPROACH...THICKER FOG STILL COVERING THE APPROACH, OTHERWISE
EXPECTING A GRADUAL IMPROVEMENT TO VFR THROUGH THE AFTERNOON.
MONTEREY BAY TERMINALS...HIGH CONFIDENCE VFR FOR THE 18Z TAFS. LIGHT
AND VARIABLE WINDS TODAY, THEN EAST TO SOUTHEAST NEAR 5 KNOTS EXCEPT
INCREASING TO 10 TO 12 KNOTS IN THE SALINAS VALLEY TONIGHT AND THURSDAY
MORNING.
MARINE
(TODAY THROUGH MONDAY)
ISSUED AT 822 AM PST WED DEC 18 2024
DENSE FOG ACROSS THE SAN FRANCISCO BAY UNTIL 11 AM TODAY. LOCALLY
MODERATE WINDS ARE POSSIBLE ACROSS THE SOUTHERN COASTAL WATERS
THROUGH MID MORNING WITH LIGHT WINDS THEN EXPECTED TO THEN
CONTINUE THROUGH THURSDAY. MODERATE TO LONG PERIOD NORTHWESTERLY
TO 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 ARRIVES FRIDAY INTO THE
WEEKEND BRINGING LIGHT TO MODERATE RAIN, FRESH TO STRONG WINDS,
AND ELEVATED WAVE HEIGHTS BETWEEN 15 TO 19 FEET. THIS WILL RESULT
IN DANGEROUS CONDITIONS FOR SMALL CRAFTS FRIDAY INTO THE WEEKEND.
BEACHES
ISSUED AT 1036 AM PST WED DEC 18 2024
A BEACH HAZARDS STATEMENT WILL BE IN EFFECT FROM 6 PM TODAY 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. THE COMBINATION OF ELEVATED SNEAKER WAVE THREAT AND 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 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...BEACH HAZARDS STATEMENT FROM 6 PM PST THIS EVENING THROUGH
THURSDAY AFTERNOON FOR CAZ006-505-509-529-530.
PZ...NONE.
SHORT TERM...DIALH
LONG TERM....DIALH
AVIATION...CANEPA
MARINE...CANEPA
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