912
FXUS66 KMTR 151917
AFDMTR
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SAN FRANCISCO CA
1117 AM PST MON DEC 15 2025
..NEW AVIATION, MARINE
KEY MESSAGES
UPDATED AT 343 AM PST MON DEC 15 2025
- DENSE FOG WILL CONTINUE TO IMPACT BAYSHORE, COASTAL, AND VALLEY
LOCATIONS THROUGH THE MORNING
- WET WEATHER RETURNS LATE TODAY AND PERSISTS THROUGH THE WEEK
AND LIKELY INTO NEXT WEEK
UPDATE
ISSUED AT 822 AM PST MON DEC 15 2025
NEAR TERM WEATHER IMPACTS ARE ALL ABOUT FOG. CURRENT
OBSERVATIONS, WEBCAMS, AND SATELLITE IMAGERY INDICATE DENSE FOG
ACROSS INLAND VALLEYS, WEST DELTA, AND BAYS. AS A RESULT, A DENSE
FOG ADVISORY WAS ISSUED EARLIER THIS MORNING. THE ADVISORY IS
SLATED TO EXPIRE AT 11 AM, WHICH SEEMS REASONABLE AT THIS TIME
GIVEN LIGHT WINDS AND HIGH CIRRUS FILTERING OVER THE BAY AREA.
NO UPDATES AT THIS TIME, BUT WILL MONITOR HOW THE FOG LINGERINGS
THROUGH THE MORNING.
AFTERNOON FORECAST UPDATE WILL FOCUS ON RAIN CHANCES THE NEXT
24-48HR AND A MORE NOTABLE PATTERN CHANGE IN THE 7-10 DAY
TIMEFRAME. SEE BELOW FOR THOSE PATTERN CHANGES...
SHORT TERM
ISSUED AT 343 AM PST MON DEC 15 2025
(TODAY AND TONIGHT)
TODAY WILL START OFF FOGGY ONCE AGAIN FOR BAYSHORE, COASTAL, AND
VALLEY LOCATIONS. LOW VISIBILITY COULD MAKE DRIVING CONDITIONS
HAZARDOUS. 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.
A CHANGE IS ON THE WAY THOUGH! IN FACT IT CAN BE SEEN IN THE FORM OF
HIGH CLOUDS STREAMING IN FROM THE WEST. THESE HIGH CLOUDS ARE
ASSOCIATED WITH A STORM FORCE LOW OFF THE COAST OF THE
OREGON/WASHINGTON BORDER THAT IS HEADED TO BRITISH COLUMBIA. THE
ACCOMPANYING COLD FRONT WILL LOSE STEAM AS IT APPROACHES THE AREA,
ALL BUT BECOMING STATIONARY. WHILE RAINFALL IS POSSIBLE AS EARLY AS
TONIGHT, IT WILL MORE THAN LIKELY HAVE TO WAIT UNTIL TOMORROW. THIS
IS WHEN SOME FORM OF UPPER-LEVEL SUPPORT (LONGWAVE TROUGH) SKIRTS
THE REGION. THE AFOREMENTIONED FEATURE WILL ACT TO SWEEP THROUGH
WHAT IS LEFT OF THE FIRST COLD FRONT BY BRINGING A GALE FORCE LOW
AND ITS ATTENDANT COLD FRONT ALONG WITH IT. RAINFALL WILL BE LIGHT
AND BENEFICIAL, GENERALLY REMAINING CONFINED NORTH OF THE GOLDEN
GATE WITH THE CENTRAL COAST REMAINING DRY OUTSIDE OF MAYBE SOME
COASTAL/HIGHER TERRAIN DRIZZLE. PROBABLY OF MORE INTEREST IS THAT
THIS PATTERN CHANGE WILL FINALLY PUT AT LEAST A TEMPORARY END TO THE
GLOOMY DAYS AS THE ATMOSPHERE BECOMES TOO TURBULENT TO SUPPORT
RADIATION FOG.
LONG TERM
ISSUED AT 343 AM PST MON DEC 15 2025
(TUESDAY THROUGH SUNDAY)
SOME LINGERING RAIN SHOWERS ARE POSSIBLE WEDNESDAY AND THURSDAY, BUT
GENERALLY SPEAKING IT WILL BE DRY. THE NEXT SYSTEM ARRIVES FRIDAY AS
A SURFACE LOW PRESSURE SYSTEM ENTERS INTO NORTHERN CALIFORNIA. THE
ATTENDANT COLD FRONT WILL BECOME A STATIONARY FRONT SATURDAY INTO
SUNDAY. THIS WILL BE THE THING TO WATCH AS STATIONARY FRONTS OFFER
AN AREA OF CONVERGENCE AND ARE A CONVEYOR BELT OF MOISTURE. STILL,
AS OF NOW, EVERYTHING THIS WEEK SEEMS BENEFICIAL, ESPECIALLY COMING
OFF OF A NOTABLE DRY SPELL FOR NOVEMBER/DECEMBER. WHEN ALL IS SAID
AND DONE, THE OFFICIAL RAINFALL TOTAL FORECAST FOR THE WEEK (MONDAY
THROUGH SUNDAY) HAS 2.50"-4.00" FOR THE HIGHER TERRAIN OF THE NORTH
BAY, 1.25"-2.50" FOR NORTH BAY INTERIOR VALLEYS, 0.50"-1.25" FOR THE
EAST BAY, SOUTH BAY, SAN FRANCISCO PENINSULA, AND CENTRAL COAST, AND
0.50" OR LESS FOR THE INTERIOR CENTRAL COAST.
THE CLIMATE PREDICTION CENTER CONTINUES TO HIGHLIGHT A MODERATE RISK
FOR PRECIPITATION MONDAY, DECEMBER 22ND THROUGH FRIDAY, DECEMBER
26TH, MODERATE RISK FOR HIGH WINDS MONDAY, DECEMBER 22ND THROUGH
SUNDAY, DECEMBER 28TH, AND A HIGH RISK FOR PRECIPITATION FOR THE
NORTH BAY MONDAY, DECEMBER 22ND THROUGH THURSDAY, DECEMBER 25TH. ALL
OF THE RAINFALL THAT WE RECEIVE THIS PRECEDING WEEK WILL
UNDOUBTEDLY PLAY A ROLE IN POTENTIAL IMPACTS NEXT WEEK.
AVIATION
(18Z TAFS)
ISSUED AT 1117 AM PST MON DEC 15 2025
IT WAS A FOGGY START TO THE MORNING ACROSS THE BAY AREA WITH FOG
LINGERING OVER THE MAJORITY OF THE SF BAY TERMINALS. CONFIDENCE IS
INCREASING THAT WE WILL SEE CLEARING ALONG THE BAY SHORELINE BY LATE
THIS MORNING AS CLOUD COVER STARTS TO BREAK UP OVER THE BAY.
STARTING TO SEE SOME IMPROVEMENTS IN VISIBILITY AS WELL WHICH
SUGGESTS FOG CHANCES ARE DIMINISHING. FOG IS LIKELY TO RETURN AGAIN
TONIGHT INTO TOMORROW MORNING BUT AN INCOMING WEAK SYSTEM MAY IMPACT
THE TIMING OF FOG RETURNING. CURRENT THINKING IS THAT WE WILL HAVE
ONE MORE NIGHT OF FOGGY CONDITIONS (MONDAY INTO TUESDAY) WITH THE
SYSTEM SET TO ARRIVE LATER IN THE DAY ON TUESDAY. KEPT THE OVERALL
TIMING SIMILAR TO PERSISTENCE BUT MADE SOME MINOR ADJUSTMENTS TO THE
ARRIVAL TIMING OF FOG.
VICINITY OF SFO...FOG/STRATUS IS CLEARING OVER THE NORTHERN PORTIONS
OF THE SF BAY WHICH HAS ALLOWED CONDITIONS TO IMPROVE DIRECTLY OVER
SFO. CONFIDENCE IS LOW TO MEDIUM ON THE RETURN OF STRATUS AND FOG
TONIGHT WITH CURRENT THINKING LEANING MORE TOWARDS STRATUS IMPACTING
SFO. LAMP GUIDANCE SHOWS INCREASING LIKELIHOOD OF STRATUS AFTER 08Z
WITH HIGHEST CONFIDENCE IN STRATUS RETURNING BY 09Z. FOR NOW, KEPT
IN LINE WITH MOS GUIDANCE SHOWING A SLIGHTLY EARLIER RETURN BY 06Z
BUT THIS MAY NEED TO BE PUSHED BACK DEPENDING ON HOW FAST STRATUS IS
ABLE TO RETURN TONIGHT. CONFIDENCE IS LOW THAT DENSE FOG WILL
DIRECTLY IMPACT SFO BUT SOME REDUCTION IN VISIBILITIES IS EXPECTED
OVERNIGHT. CONFIDENCE IS MODERATE THAT MVFR STRATUS WILL PERSIST FOR
MUCH OF TOMORROW AS A RESULT OF THE APPROACHING SYSTEM.
SFO BRIDGE APPROACH...LOCALIZED FOG/STRATUS IS EXPECTED WITHIN THE
SOUTHERN SAN FRANCISCO BAY ALONG THE BRIDGE APPROACH THROUGH EARLY
THIS AFTERNOON. FOG IS DISSIPATING MORE SLOWLY OVER THE BAY WITH
LOCALIZED DENSE FOG (1/4SM VIS) EXPECTED TO CONTINUE. SATELLITE
SHOWS THE FOG IS BEGINNING TO ERODE WHICH INCREASES CONFIDENCE THAT
THE BRIDGE APPROACH WILL SEE VAPS FOR AT LEAST SOME PORTION OF THE
AFTERNOON.
MONTEREY BAY TERMINALS...FOG HAS LARGELY DISSIPATED ACROSS THE
CENTRAL COAST WITH VISIBILITIES IMPROVING AND CLOUD COVER
DISSIPATING. LOW TO MODERATE CONFIDENCE IN THE RETURN OF FOG
TONIGHT. LEANED ON A MIXTURE OF PERSISTENCE AND LAMP GUIDANCE TO
PUSH THE RETURN OF LOWER VISIBILITIES BACK TONIGHT. WINDS GENERALLY
STAY LIGHT BUT A MORE MODERATE SEA BREEZE IS EXPECTED ALONG THE
COAST DURING THE AFTERNOON/EVENING HOURS.
MARINE
(TODAY THROUGH SATURDAY)
ISSUED AT 1117 AM PST MON DEC 15 2025
SOUTHERLY FLOW WILL PREVAIL NORTH OF PIGEON POINT AHEAD OF AN
APPROACHING FRONTAL SYSTEM. DENSE FOG CONTINUES ACROSS THE
MONTEREY BAY AND SAN FRANCISCO BAY. CONDITIONS ARE LIKELY TO
IMPROVE BY LATE THIS MORNING BUT PATCHY DENSE FOG IS LIKELY TO
PERSIST IN THE NORTHERN SAN FRANCISCO BAY AND WEST DELTA INTO THE
AFTERNOON. MODERATE TO FRESH WINDS CONTINUE ACROSS THE SOUTHERN
WATERS WITH PERIODS OF MODERATE WINDS EXPECTED ACROSS THE
NORTHERN WATERS. A WEAK SYSTEM WILL BRING MODERATE LONG PERIOD
NORTHWEST SWELL TUESDAY INTO THE WEEKEND. MODERATE SEAS RETURN
WITH WAVE HEIGHTS BUILDING UP TO 9 FEET. RAIN CHANCES INCREASE
LATE TONIGHT AND REMAIN ELEVATED THROUGH THE END OF THE FORECAST
PERIOD.
MTR WATCHES/WARNINGS/ADVISORIES
CA...NONE.
PZ...SMALL CRAFT ADVISORY FROM 3 PM THIS AFTERNOON TO 9 PM PST
TUESDAY FOR PT PINOS TO PT PIEDRAS BLANCAS 0-10 NM.
SHORT TERM...SARMENT
LONG TERM....SARMENT
AVIATION...KENNEDY
MARINE...KENNEDY
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