927
FXUS66 KMTR 202357
AFDMTR
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SAN FRANCISCO CA
357 PM PST SAT DEC 20 2025
..NEW SHORT TERM, LONG TERM
KEY MESSAGES
UPDATED AT 346 PM PST SAT DEC 20 2025
- FLOOD WATCH IN EFFECT NOW THROUGH MONDAY AFTERNOON ACROSS THE
NORTH BAY
- MODERATE TO HEAVY RAINFALL TONIGHT INTO EARLY SUNDAY ACROSS THE
NORTH BAY
- LIGHT TO MODERATE RAIN SHIFTS SOUTH ONCE AGAIN TO BAY AREA AND
CENTRAL COAST DURING THE DAY SUNDAY
- IMPACTFUL AND HAZARDOUS WIND TUESDAY THROUGH FRIDAY ALONG OUR
ENTIRE COASTLINE, AND HIGHER ELEVATIONS INLAND
- HAZARDOUS BEACH CONDITIONS LIKELY WEDNESDAY THROUGH FRIDAY FOR
ALL PACIFIC COAST BEACHES
SHORT TERM
ISSUED AT 346 PM PST SAT DEC 20 2025
(THIS EVENING THROUGH SUNDAY)
THE ATMOSPHERIC RIVER MOISTURE PLUME CONTINUES TO OSCILLATE THIS
AFTERNOON, THE FOCUS HAS BEEN ON THE BAY AREA SINCE MID-MORNING AND
WILL THEN GRADUALLY MOVE BACK TOWARD THE NORTH BAY TONIGHT INTO
EARLY TOMORROW MORNING. AFTER SUNRISE SUNDAY, WE'LL SEE A NOTABLE
SHIFT SOUTH TOWARD THE CENTRAL COAST AS THE UPPER LEVEL TROUGH
ASSOCIATED WITH THE STRENGTHENING SYSTEM IN THE GULF OF ALASKA
DEEPENS. THE TWENTY-FOUR HOUR RAINFALL TOTALS IN THE NORTH BAY ARE
AHEAD OF PACE, WITH THE FLOOD WATCH BEGINNING THIS AFTERNOON AND
PERIODS OF MODERATE TO HEAVY RAINFALL EXPECTED OVERNIGHT WITHIN THE
AREA COVERED BY THE WATCH.
SATELLITE IMAGERY THIS AFTERNOON SHOWS A LARGE CLOUD SHIELD
EXTENDING FROM MONTEREY BAY WELL NORTH INTO SOUTHERN OREGON. THE
COMBINATION OF A SURFACE TROUGH SHIFTING SOUTH FROM NORCAL TO THE
SANTA CRUZ MOUNTAINS BY LATE SUNDAY, A FULLY SATURATED BOUNDARY
LAYER UP TO 850MB AND CONTINUOUS SHORTWAVE ENERGY EMBEDDED IN THE
500MB FLOW WILL RESULT IN RAINFALL TOTALS ACROSS THE NORTH BAY
AROUND 2-3" IN THE VALLEYS AND OTHER LOW-LYING AREAS, WITH HIGHER
ELEVATIONS POTENTIALLY SEEING UP TO 6" OR MORE LOCALLY. THE MARK
WEST CREEK NEAR MIRABEL HEIGHTS IS FORECAST TO REACH ACTION STAGE
BY LATE SUNDAY EVENING, TRAVELERS SHOULD BE CAUTIOUS DRIVING
THROUGH THROUGH THE NORTH BAY FOR THE REMAINDER OF THE EXTENDED
FORECAST.
LONG TERM
ISSUED AT 346 PM PST SAT DEC 20 2025
(SUNDAY NIGHT THROUGH NEXT FRIDAY)
MONDAY OFFERS A BIT OF A REPRIEVE FOR THE NORTH BAY AS THE
ATMOSPHERIC RIVER MOISTURE PLUME IS ONCE AGAIN PUSHED SOUTH TOWARD
THE SANTA CRUZ MOUNTAINS AND THE REMAINDER OF THE CENTRAL COAST. THE
DEEPENING AND EXPANDING UPPER LOW MOVING SOUTH OUT OF THE GULF OF
ALASKA BEGINS TO ASSERT ITS INFLUENCE OVER THE SYNOPTIC PATTERN AT
OUR LATITUDE. AS THE ATMOSPHERE RESETS TO THE WEST OVER OPEN
WATER WE'LL STILL SEE SCATTERED LIGHT RAIN ACROSS MOST OF OUR AREA
DURING THE DAY MONDAY WITH MINIMAL IMPACTS.
BY TUESDAY, SOME UNCERTAINTY IS INTRODUCED INTO THE FORECAST. THE
MOST RECENT GUIDANCE SUGGEST A LESS DYNAMIC SURFACE RESPONSE TO
THE DEEPENING TROUGH OFFCOAST, ESPECIALLY EARLY ON. PREVIOUS
GUIDANCE INDICATED RAPID SURFACE PRESSURE FALLS DURING THE DAY
TUESDAY, WITH THE STRONG AREA OF LOW PRESSURE TAKING AIM AT THE
BAY AREA/NORTH BAY BY LATE TUESDAY NIGHT. TUESDAY INTO WEDNESDAY
IS NOW IN THE LATER TIME FRAME OF HIGHER RESOLUTION DATA AS WELL,
WITH THE NAM12 INDICATING A LESS ORGANIZED RESPONSE AT THE
SURFACE OVER THAT SAME TIME FRAME AS WELL. DETERMINISTIC GUIDANCE
DEPICTS A MORE ORGANIZED SURFACE RESPONSE LATER IN THE FORECAST
PERIOD AND FARTHER NORTH OFF THE COAST OF NORCAL BY LATE WEDNESDAY
NIGHT. THE DIFFERENCES ARE SOMEWHAT SUBTLE AND CONFIDENCE FOR
IMPACTFUL RAINFALL ACROSS THE NORTH BAY BETWEEN NOW AND THE END OF
THE WEEK REMAINS VERY HIGH.
FOR THE MOST PART ALL THE ENSEMBLE MEMBERS HAVE BEGUN TO PICK UP ON
THE SUBTLE CHANGES IN THE SURFACE RESPONSE AND PATTERN. WHILE SOME
OF THE INLAND RAINFALL TOTALS MAY COME DOWN SOMEWHAT AS WE MOVE
THROUGH THE WEEK, THE PATTERN REMAINS WET THROUGHOUT OUR ENTIRE
FORECAST AREA AND TRAVEL IMPACTS WILL PERSIST, ESPECIALLY THE
FARTHER NORTH YOU ARE. STORM FORCE TO NEAR HURRICANE FORCE WINDS
AT TIMES UP AND DOWN OUR COAST TUESDAY THROUGH EARLY FRIDAY WILL
CONTINUE TO PRODUCE EXCEPTIONALLY DANGEROUS CONDITIONS ALONG OUR
COASTAL BEACHES AND COASTAL WATERS.
AVIATION
(18Z TAFS)
ISSUED AT 951 AM PST SAT DEC 20 2025
FOG AND LOW CLOUDS CONTINUE TO PLAGUE THE NORTH BAY TERMINALS THIS
MORNING, WITH LIFR CONDITIONS PREVAILING, DESPITE RAIN STARTING TO
FILL IN ACROSS THE REGION. ELSEWHERE, MVFR CONDITIONS WILL
CONTINUE TO PERSIST, BUT MAY TEMPORARY DROPS TO IFR AND LIFR CIGS
ARE POSSIBLE THROUGH LATE THIS MORNING. GUIDANCE CONTINUES TO
FAVOR IFR CIGS, BUT CIGS ARE CURRENTLY RANGING BETWEEN IFR AND
MVFR. SIMILARLY, GUIDANCE IS SHOWING MORE SIGNIFICANT DROPS IN
VISIBILITY WHILE OBS SHOW IT REMAINING LARGELY STABLE SO FAR.
THINKING IS THAT VISIBILITY WILL INITIALLY REMAIN MORE STABLE BUT
DECREASE AS MORE PERSISTENT MODERATE SHOWERS ARRIVE THIS
AFTERNOON/TONIGHT. WINDS STRENGTHEN TOWARDS THE END OF THE TAF
PERIOD WITH GUSTS IN EXCESS OF 20 TO 25 KNOTS POSSIBLE ALONG THE
COAST, NORTH BAY, AND SF BAY SHORELINE.
VICINITY OF SFO...LIGHT SHOWERS ARE MOVING THROUGH THE BAY AREA WITH
CEILING HEIGHTS FLUCTUATING BETWEEN MVFR AND VFR. MODERATE
CONFIDENCE THAT MVFR CIGS WILL GENERALLY PREVAIL THROUGH THE
AFTERNOON AS THE RAIN FILLS IN ACROSS THE REGION TODAY. SFO IS
CURRENTLY ON THE SOUTHERN EDGE OF THE RAIN BAND, SO IF IT SAGS
SOUTHWARD THROUGH THE DAY, THINK THERE IS A GOOD CHANGE (60%) OF
MVFR CIGS AND RAIN PREVAILING THROUGH THE DAY. WINDS STRENGTHEN BY
MID TO LATE TOMORROW MORNING WITH GUSTS BETWEEN 25 TO 30 KNOTS
LIKELY.
SFO BRIDGE APPROACH...SIMILAR TO SFO.
MONTEREY BAY TERMINALS...CIGS REMAIN ON THE IFR-MVFR BORDER WITH
LIGHT OFFSHORE WINDS CONTINUING. SHOWERS ARE DEVELOPING IN THE
VICINITY OF MRY AND SNS OVER THE MONTEREY BAY, BUT THEY ARE NOT
EXPECTED TO CAUSE ANY MAJOR IMPACTS TODAY. RAIN SHOWERS BECOME
MORE WIDESPREAD TONIGHT INTO TOMORROW MORNING, WITH LIGHT TO
MODERATE RAIN REACHING BOTH TERMINALS BY 08/09Z TOMORROW.
GENERALLY EXPECTING OVERCAST CONDITIONS TO PERSIST FOR MUCH OF
TODAY, BUT MAY SEE SOME CLEARING AT SNS DURING THE AFTERNOON.
MARINE
(TODAY THROUGH THURSDAY)
ISSUED AT 918 AM PST SAT DEC 20 2025
WET AND UNSETTLED WEATHER TO PREVAIL THROUGH TUESDAY, WITH
INCREASING COVERAGE IN THE SHOWERS ACTIVITY TODAY. RAIN INTENSITY
INCREASES OVER THE NORTHERN WATERS BY SUNDAY. WINDS REMAIN LIGHT
AND SOUTHERLY THROUGH TONIGHT WHEN WINDS STRENGTHEN TO FRESH TO
LOCALLY STRONG AHEAD OF COLD FRONTAL PASSAGE SUNDAY INTO MONDAY.
WINDS DIMINISH EARLY MONDAY BEFORE RESTRENGTHENING LATE TUESDAY AS
A MORE SUBSTANTIAL, STRONGER SYSTEM ARRIVES TUESDAY INTO
WEDNESDAY. THIS SYSTEM WILL BRING WIDESPREAD GALE FORCE TO NEAR
GALE FORCE WINDS AND THE POTENTIAL FOR ISOLATED HURRICANE FORCE
GUSTS ACROSS THE INTERIOR COASTAL WATERS FROM POINT SUR TO POINT
PINOS. SEAS BUILD THROUGH THE SECOND HALF OF NEXT WEEK, BECOMING
VERY HAZARDOUS FOR MARINERS WITH THE POTENTIAL FOR WAVE HEIGHTS IN
EXCESS OF 20 FEET.
MTR WATCHES/WARNINGS/ADVISORIES
CA...FLOOD WATCH THROUGH MONDAY AFTERNOON FOR CAZ502>506.
PZ...SMALL CRAFT ADVISORY FROM 9 PM THIS EVENING TO 9 PM PST SUNDAY
FOR PT ARENA TO PT REYES 0-10 NM-PT ARENA TO PT REYES 10-60
NM-PT REYES TO PIGEON PT 0-10 NM-SF BAY N OF BAY BRIDGE.
SMALL CRAFT ADVISORY FROM 9 AM TO 9 PM PST SUNDAY FOR MRY BAY-PT
PINOS TO PT PIEDRAS BLANCAS 0-10 NM.
SMALL CRAFT ADVISORY FROM 3 AM TO 9 PM PST SUNDAY FOR PIGEON PT
TO PT PINOS 0-10 NM-PIGEON PT TO PT PINOS 10-60 NM.
SHORT TERM...JM
LONG TERM....JM
AVIATION...PALMER
MARINE...PALMER
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