914
FXUS66 KMTR 190532
AFDMTR
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SAN FRANCISCO CA
932 PM PST THU DEC 18 2025
..NEW AVIATION, MARINE
KEY MESSAGES
UPDATED AT 317 PM PST THU DEC 18 2025
- AREAS OF DENSE FOG EXPECTED ONCE AGAIN TONIGHT
- MOSTLY LIGHT, BENEFICIAL RAINFALL LATE TONIGHT THROUGH SATURDAY
- SLIGHT CHANCE OF THUNDERSTORMS WITH INCREASING COVERAGE OF
RAINFALL AND GUSTY WINDS SUNDAY AFTERNOON AND EVENING
- WIDESPREAD SPREAD RAINFALL MODERATE TO HEAVY AT TIMES, GUSTY
WINDS, INCREASING CHANCES OF FLOODING AND TRAVEL IMPACTS
TUESDAY THROUGH THURSDAY (CHRISTMAS)
- PATTERN APPEARS TO REMAIN UNSETTLED BEYOND THE HOLIDAY INTO
NEXT WEEKEND
UPDATE
ISSUED AT 806 PM PST THU DEC 18 2025
WE JUST SWITCHED THE RADAR TO PRECIP MODE WHERE IT WILL REMAIN FOR
QUITE SOME TIME. VERY LIGHT RAIN HAS MOVED INTO THE NORTH BAY.
THIS IS ON THE SOUTHERN PERIPHERY OF AN ATMOSPHERIC RIVER
CURRENTLY PUMPING A BAND OF MOISTURE FROM HAWAII TO OREGON. LIGHT
AND BRIEF ISOLATED SHOWERS WILL CONTINUE IN THE NORTH BAY THROUGH
THE NIGHT BEFORE A MORE ORGANIZED BAND OF MORE MODERATE RAIN
PUSHES THROUGH FRIDAY AFTERNOON. WHILE MOSTLY LIGHT, THIS WILL BE
THE FIRST ROUND OF WHAT WILL BECOME A VERY WET WEEK. THE LATEST
FORECAST TREND HAS PUSHED THE TIMING OF THE HEAVIER RAIN BACK
ABOUT 12 HOURS, WHILE THE TOTAL ACCUMULATION HAS TRENDED HIGHER.
SPECIFICALLY THE 3RD ROUND OF RAIN FROM TUESDAY THROUGH FRIDAY NOW
LOOKS AT LEAST ON PAR WITH THE 2ND ROUND FROM SATURDAY THROUGH
TUESDAY. OVER THE NEXT WEEK WE EXPECT MOST OF THE BAY AREA AND
CENTRAL COAST TO HAVE RECEIVED AROUND 5-10" OF RAIN, WITH MORE IN
THE COASTAL MOUNTAINS. IF THAT HOLDS, IT'S NEARLY 25% OF THE
NORMAL PRECIPITATION FOR THE ENTIRE YEAR AND WILL CAUSE SOME
FLOODING. THERE IS ALSO A GOOD CHANCE FOR STRONG WINDS ALL WEEK,
BUT PARTICULARLY TUESDAY NIGHT THROUGH WEDNESDAY MORNING AS A
DEEP LOW PRESSURE SYSTEM DEVELOPS AND APPROACHES THE COAST. THIS
SYSTEM COULD ALSO HELP TRIGGER SOME THUNDERSTORMS DURING THE SAME
TIME FRAME.
SHORT TERM
ISSUED AT 317 PM PST THU DEC 18 2025
(THIS EVENING THROUGH FRIDAY)
THE REMAINDER OF TODAY AND TONIGHT ACROSS OUR AREA WILL REMAIN
MOSTLY DRY WITH THE EXCEPTION OF FAR NORTHERN SONOMA COUNTY, WHICH
MAY SEE THE ONSET OF LIGHT RAIN THIS EVENING. RAINFALL IS EXPECTED
TO CONTINUE TO BE LIGHT THROUGHOUT THE DAY FRIDAY ACROSS THE
REMAINDER OF THE NORTH BAY, AND MAY SHIFT AS FAR SOUTH AS THE BAY
AREA AND EAST BAY WITH NO IMPACTS. AREAS WHERE FOG AND/OR DRIZZLE
DEVELOPED LAST NIGHT WILL LIKELY SEE SIMILAR CONDITIONS TONIGHT INTO
FRIDAY MORNING.
LONG TERM
ISSUED AT 317 PM PST THU DEC 18 2025
(FRIDAY NIGHT THROUGH NEXT WEDNESDAY)
CONFIDENCE CONTINUES TO INCREASE THAT THE OVERALL SYNOPTIC PATTERN
WILL REMAIN ACTIVE THROUGH THE EXTENDED FORECAST AND BEYOND. IF
YOU'RE A REGULAR READER OF OUR AFD'S YOU WON'T BE SURPRISED TO READ
THAT THE NORTH BAY WILL SEE THE MOST RAINFALL BOTH INITIALLY AND OVER
THE COURSE OF THE NEXT WEEK. THE RAINFALL WE SEE TOMORROW AND
THROUGH THE WEEKEND WILL BE MOSTLY ON-AND-OFF AND BENEFICIAL WITH NO
IMPACTS ANTICIPATED. WE ARE EMERGING FROM A FAIRLY DRY STRETCH OF
WEATHER SO THE SOILS WILL BE ABLE TO ABSORB THIS FIRST ROUND OF
RAINFALL FAIRLY EASILY OVER THE NEXT COUPLE OF DAYS. TRAVEL IMPACTS
ON SUNDAY WILL BE RELEGATED MOSTLY TO THE NORTH BAY AND POINTS
NORTH, WITH LIGHT TO MODERATE RAIN AT TIMES SHIFTING SOUTH INTO THE
BAY AREA, EAST BAY SOUTH BAY AND SANTA CRUZ MOUNTAINS SUNDAY
AFTERNOON INTO SUNDAY NIGHT. SUNDAY AFTERNOON AND EVENING ALSO HAS A
SLIGHT CHANCE FOR OCCASIONAL THUNDERSTORMS THAT COULD PRODUCE BRIEF
DOWNPOURS AND GUSTY WINDS UP TO 50MPH AT HIGHER ELEVATIONS, 40MPH IN
LOWER LYING AREAS ACROSS THE NORTH BAY, BAY AREA AND EAST BAY.
BY LATE SUNDAY NIGHT A STRONG AREA OF LOW PRESSURE IN THE GULF OF
ALASKA WILL CONTINUE TO DEEPEN AND EVOLVE SOUTHWARD OFFSHORE
TOWARD NORCAL OVER THE COURSE OF NEXT WEEK, PRODUCING NUMEROUS
TROUGH AXIS' THAT WILL MOVE ONSHORE ACROSS THE CALIFORNIA PACIFIC
COAST OVER THAT SAME TIME PERIOD. THE DEEPENING AREA OF LOW
PRESSURE WILL ALSO TAP INTO SOUTHERN PACIFIC MOISTURE RESULTING IN
SEVERAL WAVES OF A DEVELOPING ATMOSPHERIC RIVER AS THE SHARPENING
TROUGH AXIS' INTERACT WITH THE CONTINUOUS CONVEYOR BELT OF
MOISTURE. THERE IS PLENTY OF UNCERTAINTY IN THE EXACT TIMING AND
LOCATION OF WHERE THE HEAVIEST RAIN AND STRONGEST WINDS WILL
ULTIMATELY IMPACT OUR AREA. THE STRONGEST PORTION OF THE UPPER
LEVEL LOW ATTM APPEARS TO APPROACH THE COAST AT SOME POINT ON
WEDNESDAY BRINGING VERY STRONG WINDS ALONG THE COAST, THAT WILL
SPREAD INLAND (BUT NOT AS STRONG AS THE COAST) AND A LARGER AREA
OF MODERATE TO HEAVY RAINFALL AT TIMES WITH MORE WIDESPREAD
IMPACTS. BY THE MIDDLE OF NEXT WEEK WE CAN EXPECT THE POTENTIAL OF
NUISANCE FLOODING AT THE VERY LEAST, RISING STREAMS AND RIVERS,
DOWNED TREES AND POWERLINES, MUD/ROCK SLIDES AND DANGEROUS
MARINE/BEACH CONDITIONS.
IF YOU, YOUR FRIENDS AND RELATIVES PLAN ON TRAVELING WITHIN OUR
FORECAST AREA OVER THE NEXT WEEK PREPARE FOR DELAYS AND ALLOW MORE
TIME TO REACH YOUR DESTINATION AND IT'S IMPERATIVE TO STAY IN TUNE
WITH THE FORECAST AS WE CONTINUE TO REFINE AND ADD MORE DETAILS
TO THE WIDESPREAD IMPACTS AND HAZARDS THAT WILL DEVELOP AND
COMPOUND OVER TIME BY THE END OF NEXT WEEK AND BEYOND.
AVIATION
(06Z TAFS)
ISSUED AT 932 PM PST THU DEC 18 2025
MVFR-IFR STRATUS DEVELOPING ACROSS THE BAY AREA UNDERNEATH A THIN
LAYER OF HIGH CLOUDS, WITH THE SOUTH BAY AND CENTRAL COAST REMAINING
GENERALLY VFR FOR THE TIME BEING. STRATUS IS EXPECTED TO EXPAND
THROUGH THE NIGHT. IN THE NORTH BAY AND THE NORTHERN SF BAY
TERMINALS, LIFTING STRATUS WILL GIVE WAY TO A FRONTAL RAIN BAND WITH
MVFR CEILINGS AND IMPACTS TO VISIBILITY THROUGH FRIDAY. AT SJC AND
TO THE SOUTH, A BRIEF PERIOD OF CLEARING WILL ENSUE EARLY FRIDAY
AFTERNOON BEFORE THE FRONTAL BAND COMES IN LATE AFTERNOON THROUGH
THE EARLY EVENING HOURS. BY THE END OF THE 24-HOUR TAF PERIOD,
SHOWERY CONDITIONS WILL EXTEND ACROSS THE BAY AREA AND INTO THE
NORTH BAY WITH DRIZZLE POSSIBLE ACROSS THE MONTEREY BAY REGION.
LIGHT WINDS OVERNIGHT WILL BECOME BREEZY AND SOUTHERLY TO
SOUTHWESTERLY ON FRIDAY, LIGHTENING AGAIN IN THE EVENING HOURS.
VICINITY OF SFO... MVFR CEILINGS THROUGH THE TAF PERIOD. CHANCES FOR
SHOWERS BEGIN OVERNIGHT, BUT THE BULK OF THE CHANCES LIE TO THE WEST
OF THE TERMINAL AND THE SAN MATEO MOUNTAINS. GREATER CONFIDENCE IN
RAINFALL IN ADDITION TO GUSTY SOUTH-SOUTHWEST WINDS ARRIVING WITH
THE FRONTAL RAIN BAND FRIDAY AFTERNOON, WITH THE WINDS DECREASING
BUT THE SHOWERS CONTINUING THROUGH THE END OF THE TAF PERIOD.
SFO BRIDGE APPROACH... SIMILAR TO SFO.
MONTEREY BAY TERMINALS... VFR CONDITIONS WILL CONTINUE FOR A FEW
MORE HOURS BEFORE IFR STRATUS ROLLS IN LATER TONIGHT. STRATUS CLEARS
OUT LATE FRIDAY MORNING AS GENTLE NORTHWEST BREEZES DEVELOP. THE
MVFR CEILINGS FROM THE APPROACHING RAIN BAND WILL COME TO THE REGION
FRIDAY EVENING, WITH THE BEST CHANCES FOR SCATTERED SHOWERS COMING
AFTER THE END OF THE TAF PERIOD.
MARINE
(TONIGHT THROUGH NEXT WEDNESDAY)
ISSUED AT 932 PM PST THU DEC 18 2025
LIGHT TO MODERATE ONSHORE BREEZES PREVAIL WITH MODERATE SEAS
THROUGH LATE WEEK. RAIN CHANCES INCREASE FRIDAY WITH MODERATE TO
HEAVY RAIN OVER THE NORTHERN WATERS SUNDAY. MORE SUBSTANTIAL
RAINFALL AND A STRONG STORM SYSTEM DEVELOPS AROUND THE MIDDLE OF
NEXT WEEK.
MTR WATCHES/WARNINGS/ADVISORIES
CA...NONE.
PZ...SMALL CRAFT ADVISORY FROM 9 AM TO 3 PM PST FRIDAY FOR PT ARENA
TO PT REYES 10-60 NM.
SHORT TERM...JM
LONG TERM....JM
AVIATION...DIALH
MARINE...DIALH
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