445
FXUS66 KMTR 161056
AFDMTR
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SAN FRANCISCO CA
256 AM PST TUE DEC 16 2025
..NEW SHORT TERM, LONG TERM, MARINE
KEY MESSAGES
UPDATED AT 253 AM PST TUE DEC 16 2025
- PATCHY DENSE FOG THROUGH THE MORNING
- WET WEATHER RETURNS TODAY AND PERSISTS THROUGH THE WEEK
- CONFIDENCE IS INCREASING THAT IMPACTFUL WEATHER WILL ARRIVE FOR
NEXT WEEK'S TRAVEL
SHORT TERM
ISSUED AT 253 AM PST TUE DEC 16 2025
(TODAY AND WEDNESDAY)
TULE FOG IN THE CENTRAL VALLEY HAS SEEPED INTO THE DELTA AND
SUBSEQUENTLY INTO THE NORTH BAY INTERIOR VALLEYS AND EAST BAY
INTERIOR VALLEYS. GIVEN THE SLOWER ARRIVAL OF THE BENEFICIAL, LIGHT
RAIN AND ITS ACCOMPANYING CLOUD SHIELD, EXPECT CONDITIONS TO
DETERIORATE THROUGH THE NIGHT, ALTHOUGH THEY WILL NOT BE AS
ENCOMPASSING AS LAST NIGHT. IF DRIVING, SLOW DOWN, USE YOUR LOW-BEAM
HEADLIGHTS, AND LEAVE PLENTY OF DISTANCE AHEAD OF YOU. IF COMMUTING,
ALLOW EXTRA DRIVE TIME TO REACH YOUR DESTINATION SAFELY. NOW ONTO
THE RAIN. AS MENTIONED IT IS ARRIVING BEHIND SCHEDULE WITH NO
MEASURABLE PRECIPITATION FALLING YET. IN FACT, YOU WILL HAVE TO LOOK
UPSTREAM AT EUREKA'S RADAR (KBHX) TO SEE ANYTHING AT ALL. THERE'S
ALSO BEEN A SMALL CLUSTER OF LIGHTNING ACTIVITY ABOUT 200 MILES OFF
THE MENDOCINO COUNTY COAST JUST TO THE NORTH OF OUR AREA. THERE'S A
SLIGHT (UP TO 15% CHANCE) FOR THUNDERSTORMS TODAY FOR FAR NORTHERN
AREAS OF THE NORTH BAY AND ADJACENT COASTAL WATERS. THE CRITICAL
INGREDIENTS FOR THUNDERSTORMS OF LIFT, INSTABILITY, AND MOISTURE ARE
THERE, BUT BARELY. FRONTOLYSIS OF THE COLD FRONT AND CONDITIONALLY
UNSTABLE LAPSE RATES OF 6 DEGREES C/KM PRODUCING LOW CAPE OF 50 J/KG
ARE NOT IDEAL FOR THE FIRST TWO INGREDIENTS. MOISTURE IS HOW WE EVEN
HAVE A SLIGHT CHANCE. THE 00Z OAK SOUNDING OBSERVED A PWAT VALUE OF
0.84 INCHES WHICH IS NEAR THE 90TH PERCENTILE (0.89 INCHES) FOR THE
DATE AND TIME. THE MOISTURE TAP GOES BACK TO THE SUBTROPICS AND IS
ESSENTIALLY ON A CONVEYOR BELT BETWEEN A STORM FORCE LOW IN THE GULF
OF ALASKA AND SURFACE HIGH PRESSURE OFF THE CALIFORNIA/MEXICO
BORDER. PWATS AND IVT VALUES WILL CONTINUE TO INCREASE THROUGH THE
DAY. STILL, ONLY LIGHT AND BENEFICIAL RAIN IS EXPECTED AS OUR REGION
REMAINS ON THE PERIPHERY OF THE MAIN EVENT TO THE NORTH. MORE
BENEFICIAL LIGHT RAIN IS EXPECTED INTO WEDNESDAY AS A SECOND COLD
FRONT WRINGS OUT THE LEFTOVER MOISTURE FROM THE PAST TWO DAYS.
RAINFALL TOTALS THROUGH WEDNESDAY: COASTAL NORTH BAY UP TO 0.50",
REST OF BAY AREA LESS THAN 0.10", CENTRAL COAST COASTAL/HIGHER
TERRAIN DRIZZLE IF NOT DRY.
LONG TERM
ISSUED AT 253 AM PST TUE DEC 16 2025
(THURSDAY THROUGH MONDAY)
SOME MORE BENEFICIAL, LIGHT RAIN IS POSSIBLE THURSDAY AS THE COLD
FRONT BECOMES A STATIONARY FRONT ACROSS THE STATE OF CALIFORNIA. BY
THURSDAY, GLOBAL ENSEMBLE CLUSTERS ARE IN AGREEMENT THAT UPPER-LEVEL
HIGH PRESSURE NEAR THE CALIFORNIA/MEXICO BORDER WILL BEGIN TO WEAKEN
AND EXIT EAST THANKS TO AN ANOMALOUSLY DEEP LONGWAVE TROUGH
DEVELOPING OVER THE NORTHEAST PACIFIC OCEAN. THIS SWITCH TO
MERIDIONAL FLOW FROM ZONAL FLOW WILL ALLOW THE STORM DOOR TO OPEN.
THE NEXT SYSTEM IS A LITTLE COMPLICATED WITH THE SURFACE FEATURE
SEPARATED FROM THE MOISTURE SOURCE. WE'LL START WITH THE GALE FORCE
LOW THAT IS CURRENTLY NORTH OF HAWAII. THIS WILL MOVE VERY SLOWLY TO
THE NORTHEAST, ULTIMATELY BECOMING STATIONARY. ITS MOISTURE WILL GET
PULLED INTO A GALE FORCE LOW IN BRITISH COLUMBIA. THIS TRAJECTORY
WILL ALLOW FOR THE FIREHOSE OF MOISTURE TO GET DIRECTED AT THE
PACIFIC NORTHWEST, AT LEAST INITIALLY. THE PLUME OF MOISTURE WILL
SLINK DOWN THE WEST COAST INTO CALIFORNIA ON FRIDAY WITH A COLD
FRONT FOLLOWING SUIT ON SATURDAY. THIS WILL BRING WIDESPREAD
RAINFALL FROM NORTH TO SOUTH FRIDAY INTO SATURDAY. IT IS IMPORTANT
TO NOTE THAT EVERYTHING AS OF NOW LOOKS BENEFICIAL UP UNTIL THIS
POINT AND RAINFALL TOTALS HAVE TRENDED DOWN. YES, IT MAY RAIN EVERY
DAY BETWEEN NOW AND NEXT TUESDAY, BUT WE HAVE BEEN DRY FOR THE LAST
THREE WEEKS OR SO. THE AFOREMENTIONED PLUME OF MOISTURE THAT IS TIED
TO THE STATIONARY FRONT NORTH OF HAWAII IS EXPECTED TO GAIN STEAM
WITH THE DEVELOPMENT OF A NEW LOW AND LINGER INTO AT LEAST MONDAY
BASED ON ECMWF AND GFS IVT FORECASTS. GEFS AND ECMWF ENSEMBLE IVT
FORECASTS GENERALLY SHOW THE ENSEMBLE MEANS AND +/- 1 STANDARD
DEVIATION GENERALLY IN THE 250-500 KG/MS RANGE. RAINFALL TOTALS
THURSDAY THROUGH MONDAY: COASTAL NORTH BAY UP TO 5.00", REST OF
NORTH BAY: 1.50"-4.00", REST OF BAY AREA 0.50"-1.50", CENTRAL COAST:
0.10"-1.50". ANOTHER POTENTIAL IMPACT COULD BE WIND SUNDAY INTO
NEXT WEEK. IT IS IMPORTANT TO KNOW THAT THE DETAILS OF THE LONG
TERM FORECAST WILL BE DEPENDENT ON WHAT HAPPENS BETWEEN NOW AND
THEN AS IT WILL BE A CASE OF CUMULATIVE IMPACTS. IT IS ALSO
IMPORTANT TO NOTE THAT ANY DETAILS BEYOND SEVEN DAYS ARE BEYOND
THE REACHES OF THE OFFICIAL FORECAST AND ARE INCREDIBLY DIFFICULT
TO PREDICT WITH ANY KIND OF ACCURACY. IT CAN BE CONTINUED TO BE
SAID THOUGH THAT WE ARE EXPECTING THE WET PATTERN TO CONTINUE AT
LEAST THROUGH CHRISTMAS DAY (60% CONFIDENCE) WITH THE POTENTIAL
(20-40% CONFIDENCE) FOR IT TO LINGER THROUGH DECEMBER 29TH.
WHETHER YOU ARE TRAVELLING OR STAYING HOME FOR THE HOLIDAY, NOW IS
THE TIME TO BEGIN PREPARING BY CLEANING OUT YOUR GUTTERS AND
ENSURING THAT LOOSE OUTDOOR ITEMS ARE SECURED (LIKE YOUR CHRISTMAS
INFLATABLES). IF YOU ARE TRAVELLING OUT OF THE AREA BY CAR, PLEASE
TAKE THE WEATHER INTO ACCOUNT AND CHECK THE FORECAST OF THE
NATIONAL WEATHER SERVICE FOR THAT AREA AND THE AREAS IN BETWEEN
HERE AND THERE.
AVIATION
(06Z TAFS)
ISSUED AT 930 PM PST MON DEC 15 2025
GENERALLY VFR ACROSS THE REGION WITH SOME HIGH LEVEL CLOUDS, BARRING
SNS WHERE RADIATIVELY FORCED VISIBILITY REDUCTIONS HAVE BEGUN, AND
THE INTERIOR EASTERN BAY AREA AND THE VICINITY OF APC WHERE THE TULE
FOG HAS GROWN OVER CCR, BUT NOT LVK. WITH THE LACK OF STRATUS AND
FOG DEVELOPMENT SO FAR TONIGHT, HAVE PULLED BACK STRATUS FORMATION
TIMES ACROSS THE REGION. LOWEST CONFIDENCE FOR STRATUS FORMATION AT
THE MONTEREY BAY TERMINALS WHERE THERE IS A GOOD CHANCE BOTH MRY AND
SNS REMAIN VFR OVERNIGHT. WILL CONTINUE TO MONITOR STRATUS
DEVELOPMENT THROUGH THE NIGHT. EXPECTED ARRIVAL OF HIGH CLOUD COVER
ON TUESDAY MAKES THE CLEARING TIMES UNCERTAIN, AND OPTED TO
GENERALLY RETAIN THE PREVIOUS FORECAST. LIGHT TO GENTLE ONSHORE
BREEZES DEVELOP ON TUESDAY WITH LIGHT RAIN SHOWERS DEVELOPING IN THE
NORTH BAY, SPREADING SOUTHWARDS IN THE EVENING HOURS.
VICINITY OF SFO... VFR WITH MID- TO HIGH LEVEL CLOUDS AT PRESENT.
LATEST MODEL OUTPUT HAS DELAYED THE ONSET OF MVFR CEILINGS TO AROUND
THE 12-13Z TIMEFRAME, BUT HAVE OPTED TO PUSH THE ONSET TO 09Z TO
ACCOUNT FOR ANY INTERACTION BETWEEN COASTAL STRATUS AND TULE FOG
IMPACTS. LOW CONFIDENCE THAT DENSE FOG DIRECTLY IMPACTS THE
TERMINAL, BUT SOME REDUCTION IN VISIBILITY IS EXPECTED OVERNIGHT.
AFTERWARDS, MODERATE CONFIDENCE THAT THE STRATUS PERSISTS THROUGH
THE REST OF THE TAF PERIOD. WINDS WILL REMAIN LIGHT TO GENTLE
THROUGHOUT THE FORECAST PERIOD, WITH WEST-NORTHWEST FLOW DEVELOPING
BY TUESDAY. LOW TO MODERATE CONFIDENCE OF SHOWERS DEVELOPING AT THE
TERMINAL BY TUESDAY EVENING.
SFO BRIDGE APPROACH... LOCALIZED STRATUS AND POTENTIAL FOR DENSE FOG
IS EXPECTED TONIGHT THROUGH TUESDAY MORNING ACROSS THE SOUTHERN SAN
FRANCISCO BAY. OTHERWISE, SIMILAR TO SFO.
MONTEREY BAY TERMINALS... CONFIDENCE IN THE RETURN OF STRATUS
TONIGHT HAS DECREASED REMARKABLY AS THE STRATUS DECK REMAINS WELL
OFF THE COAST. HAVE CONVERTED THE LIFR STRATUS AND FOG FORECASTS TO
TEMPO GROUPS AS A RESULT, AND GOING BY THE LATEST MODEL OUTPUT, EVEN
THAT MIGHT BE OVERLY PESSIMISTIC. GREATER CONFIDENCE IN STRATUS
RETURNING TO THE REGION TUESDAY EVENING AS THE STRATUS DECK
INCHES ONSHORE. LIGHT DRAINAGE FLOWS CONTINUES OVERNIGHT BEFORE
LIGHT TO GENTLE NORTHWEST WINDS RESUME ON TUESDAY AFTERNOON.
MARINE
(TODAY THROUGH SUNDAY)
ISSUED AT 253 AM PST TUE DEC 16 2025
A PLUME OF HUMID AIR FROM THE PACIFIC WILL ARRIVE TODAY AND
TONIGHT AHEAD OF A COOL FRONT MOVING SOUTHEAST ACROSS THE WATERS
AND BAYS WEDNESDAY. THE INTERACTION BETWEEN THE PLUME OF HUMID
AIR, CHILLY AIR ENTRENCHED ACROSS THE BAYS AND COOL FRONT ARRIVING
WEDNESDAY WILL RESULT IN PERIODIC LIGHT RAIN, MAINLY OVER THE
NORTHERN WATERS AND BAYS LATER TODAY INTO WEDNESDAY. MODERATE SEAS
WILL PREVAIL DURING THE WEEK.
MTR WATCHES/WARNINGS/ADVISORIES
CA...NONE.
PZ...SMALL CRAFT ADVISORY UNTIL 9 PM PST THIS EVENING FOR PT PINOS TO
PT PIEDRAS BLANCAS 0-10 NM.
SHORT TERM...SARMENT
LONG TERM....SARMENT
AVIATION...DIALH
MARINE...CANEPA
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