673
FXUS66 KMTR 110959
AFDMTR
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SAN FRANCISCO CA
259 AM PDT THU SEP 11 2025
..NEW SHORT TERM, LONG TERM
KEY MESSAGES
UPDATED AT 201 PM PDT WED SEP 10 2025
- UNSETTLED WEATHER CONTINUES INTO THURSDAY
- DRIER AND SLIGHTLY WARMER WEATHER FRIDAY AND SATURDAY.
- UNSETTLED WEATHER MAY RETURN TO THE BAY AREA ON SUNDAY.
SHORT TERM
ISSUED AT 239 AM PDT THU SEP 11 2025
(TODAY AND TONIGHT)
QUICK RECAP - AFTERNOON/EVENING PRECIP HAS DIMINISHED. THERE ARE A
FEW LINGERING ECHOES ABOUT 60 MILES WEST OVER THE OCEAN AND NEAR
MONTEREY BAY, BUT THEY'RE FADING FAST. KMUX HAS BEEN RETURNED TO
SURVEILLANCE/CLEAR AIR MODE. DECENT SEPTEMBER RAINFALL AMOUNTS
RECORDED OVER THE LAST 12-18 HOURS WITH A TRACE TO NEARLY THREE
QUARTERS OF AN INCH. ONE NOTABLE RAINFALL TOTAL IS SAN JOSE, WITH
0.41 INCHES, WHICH SETS A NEW DAILY RECORD.
TODAY AND TONIGHT: WE'VE GOT ONE MORE DAY OF PRECIP CHANCES
AROUND THE BAY AREA. THE REASON? A DOUBLE-BARREL UPPER LOW
CONTINUES TO SPIN OVER FAR NORCAL, WHICH IS EMBEDDED IN A
POSITIVELY TILTED UPPER LEVEL TROUGH. MODEL GUIDANCE HAS BEEN
RATHER PERSISTENT IN KEEPING PRECIP OVER THE NORTH BAY ONCE AGAIN
THIS AFTERNOON. WEDNESDAY THERE WERE CONCERNS OF EXCESSIVE
RAINFALL AND THUNDERSTORMS, BUT THAT THREAT HAS SHIFTED FARTHER N
AND E WITH BETTER DYNAMICS TODAY. SO IS THERE A LOW CHANCE FOR
THUNDERSTORMS AGAIN THIS AFTERNOON? SPC BRINGS THE DAY ONE OUTLOOK
JUST TO THE NAPA COUNTY LINE. FURTHER ANALYSIS OF CAMS REVEALS
SOME SOLID INSTABILITY AT THE SURFACE AND JUST ABOVE THE SURFACE.
HOWEVER, LAPSE RATES ALOFT ARE MEAGER AT BEST FROM 700-500MB.
ADDITIONALLY, POINT SOUNDINGS SHOW A WEAK CAP/INVERSION AROUND
650MB DEPENDING ON YOUR MODEL OF CHOICE. GIVEN THE POSITIVE TILT
OF A WEAKENING TROUGH DON'T THINK THAT WILL BE ENOUGH TO TIP THE
SCALES TOWARD THUNDER. THEREFORE, WILL KEEP PRECIP MENTION TO
SHOWERS OVER THE NORTH BAY. THERE COULD SOME BUILD UPS OVER THE
DIABLO AND GABILAN RANGES, BUT WILL NOT MENTION PRECIP AT THIS
TIME.
OTHERWISE, SATELLITE FOG PRODUCT OVERNIGHT SHOWS A PSUEDO-MARINE
LAYER OR MORE LIKE STRATO-CU LAYER BLANKETING THE BAY AREA AND
CENTRAL COAST. THIS LAYER WILL THIN BY LATE MORNING/EARLY
AFTERNOON, BUT GIVEN THE LIFT NEARBY SOME AFTERNOON CLOUDS WILL
LINGER. SPEAKING OF THE SATELLITE. ONE CAN STILL SEE A PRONOUNCED
HEAT SIGNATURE FROM THE GARNET FIRE IN THE SIERRA.
ANY PRECIP WILL DIMINISH BY TONIGHT AS THE LOW/TROUGH MOVE
EASTWARD AND WEAKENS FURTHER. IN ITS WAKE SUBSIDENCE DEVELOPS
WITH A REDEVELOPING MARINE LAYER AROUND 2K FEET.
LONG TERM
ISSUED AT 259 AM PDT THU SEP 11 2025
(FRIDAY THROUGH WEDNESDAY)
WARMER AND DRIER CONDITIONS DEVELOP ON FRIDAY AND INTO SATURDAY
THANKS TO SHORTWAVE RIDGING THAT DEVELOPS BEHIND THE DEPARTING
UPPER LOW. NIGHT AND MORNING MARINE LAYER CLOUDS WILL RETURN, BUT
COMPRESSED SLIGHTLY. TEMPERATURES RETURN TO THE 70S AND 80S WITH
INTERIOR CENTRAL COAST REACHING THE 90S.
A LITTLE BIT OF A ROLLER COAST TEMP-WSIE AS TEMPS DIP SLIGHTLY ON
SUNDAY THANKS TO A PASSING FRONT TO THE NORTH. A FEW SHOWERS
OVER THE NORTHERN COASTAL WATERS, BUT BY THE TIME THEY REACH THE
NORTH BAY THEY FALL APART.
EARLY NEXT WEEK LONGWAVE PATTERN CONTINUES TO FAVOR RIDGING OVER
THE WEST WITH A LOW/TROUGH NORTHERN ROCKIES. A FEW OF THE
ENSEMBLESEVEN SHOW SOME WEAK OFFSHORE FLOW AROUND SEPT 16.
AVIATION
(06Z TAFS)
ISSUED AT 916 PM PDT WED SEP 10 2025
SHOWERS HAVE ENDED AS THE MARINE LAYER STARTS TO REORGANIZE
TONIGHT. AS THE ATMOSPHERIC STABILITY RETURNS IN THE LOW LEVELS,
CUMULUS CLOUDS WILL TRANSFORM INTO A MORE UNIFORM STRATUS LAYER.
WHILE THE CLOUD COVERAGE WILL BE MORE EXTENSIVE THAN LAST NIGHT,
THERE IS STILL ENOUGH MIXING IN THE DEEP BOUNDARY LAYER TO KEEP
CEILINGS IN THE MVFR CATEGORY FOR ALL TERMINALS THROUGH THE NIGHT.
VICINITY OF SFO...FAIRLY HIGH CONFIDENCE IN MVFR CEILINGS THROUGH
THE NIGHT, ALTHOUGH THERE IS A 25% CHANCE FOR IFR CONDITIONS TO
SNEAK IN SOMETIME BEFORE 18Z. WHILE SOME GUIDANCE IS ACTUALLY
SUGGESTING CEILINGS WILL PERSIST THROUGH THE DAY TOMORROW, THE
TAFS ARE MORE OPTIMISTIC WITH VFR CONDITIONS IN THE AFTERNOON AND
EARLY EVENING. BASED ON THE CEILING HEIGHT, DRYING TREND, AND
COMPRESSING MARINE LAYER, THIS SEEMS MORE REASONABLE. OTHERWISE
MODERATE WESTERLY WINDS ARE EXPECTED FOR A FEW HOURS IN THE
AFTERNOON BEFORE DECREASING IN THE EVENING.
SFO BRIDGE APPROACH...SIMILAR TO SFO.
MONTEREY BAY TERMINALS...A POCKET OF DRY AIR APPROACHING THE COAST
MAKES THE SHORT TERM FORECAST A LITTLE TRICKY. THE WELL
ESTABLISHED CEILINGS MAY BREAK FOR A COUPLE HOURS BEFORE
RETURNING AROUND MIDNIGHT. FAIRLY HIGH CONFIDENCE IN A CLEARING
TREND FROM LATE MORNING THROUGH THE AFTERNOON BEFORE CEILINGS
RETURN THURSDAY EVENING AND THE PATTERN RETURNS TO THE TYPICAL
MARINE LAYER SET-UP.
MARINE
(TONIGHT THROUGH NEXT TUESDAY)
ISSUED AT 916 PM PDT WED SEP 10 2025
BUOY AND SATELLITE DATA CONFIRM GENTLE TO MODERATE NW WINDS AND
MODERATE SEA HEIGHTS ACROSS THE COASTAL WATERS. SIMILAR
CONDITIONS WILL PERSIST THROUGH THURSDAY BEFORE STRONGER NW WINDS
AND ROUGH SEAS ARRIVE EARLY FRIDAY. CONDITIONS WILL BRIEFLY
IMPROVE SATURDAY BEFORE FRESH TO STRONG NORTHERLY WINDS RETURN
LATE SUNDAY, REBUILDING ROUGH SEAS IN THE NORTHERN WATERS.
MTR WATCHES/WARNINGS/ADVISORIES
CA...NONE.
PZ...SMALL CRAFT ADVISORY FROM 3 PM TO 9 PM PDT FRIDAY FOR MRY BAY-
PIGEON PT TO PT PINOS 0-10 NM-SF BAY N OF BAY BRIDGE.
SMALL CRAFT ADVISORY FROM 9 PM THIS EVENING TO 3 AM PDT SATURDAY
FOR PT ARENA TO PT REYES 0-10 NM-PT ARENA TO PT REYES 10-60
NM.
SMALL CRAFT ADVISORY FROM 9 PM THIS EVENING TO 9 AM PDT FRIDAY
FOR PT PINOS TO PT PIEDRAS BLANCAS 0-10 NM.
SMALL CRAFT ADVISORY FROM 3 PM FRIDAY TO 3 AM PDT SATURDAY FOR
PIGEON PT TO PT PINOS 10-60 NM-PT PINOS TO PT PIEDRAS
BLANCAS 0-10 NM.
SMALL CRAFT ADVISORY FROM 9 PM THIS EVENING TO 3 AM PDT FRIDAY
FOR PIGEON PT TO PT PINOS 10-60 NM.
SHORT TERM...MM
LONG TERM....MM
AVIATION...FLYNN
MARINE...FLYNN
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