379
FXUS66 KMTR 111540
AFDMTR
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SAN FRANCISCO CA
840 AM PDT THU SEP 11 2025
..NEW UPDATE, MARINE
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.
UPDATE
ISSUED AT 834 AM PDT THU SEP 11 2025
SATELLITE IMAGERY SHOWS EXTENSIVE STRATUS COVERAGE ACROSS THE BAY
AREA AND CENTRAL COAST, EXPECTED TO CONTINUE DIMINISHING THROUGH
THE MORNING HOURS. MAIN FOCUS FOR TODAY REMAINS THE CHANCES FOR
SHOWERS IN THE NORTH BAY THROUGH THE AFTERNOON AND EVENING HOURS.
CHANCES REMAIN SLIGHT BUT STILL PRETTY SIGNIFICANT (15-30%
PROBABILITY) ACROSS NORTHERN AND CENTRAL SONOMA AND NAPA COUNTIES,
BUT ACCUMULATIONS SHOULD REMAIN BELOW A TENTH OF AN INCH.
MEANWHILE, NOT EXPECTING AS MUCH OF A DIP IN TEMPERATURES ON
SUNDAY WITH THE MODELS SHOWING MORE OF A ZONAL UPPER LEVEL FLOW
OVER CENTRAL CALIFORNIA, AS OPPOSED TO A SLIGHTLY MORE PRONOUNCED
TROUGHING PATTERN WHICH WAS DEPICTED IN MODEL RUNS AT THIS TIME
YESTERDAY. NO OTHER CHANGES TO THE FORECAST.
DIALH
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-WISE 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
ENSEMBLES EVEN SHOW SOME WEAK OFFSHORE FLOW AROUND SEPT 16.
AVIATION
(12Z TAFS)
ISSUED AT 448 AM PDT THU SEP 11 2025
MVFR CIGS TO CONTINUE THROUGH LATE MORNING. CONFIDENCE IS MODERATE
IN THE TIMING OF STRATUS CLEARING THIS MORNING WITH WITH GUIDANCE
SUGGESTING MOST SITES CLEARING BY 18/19Z. FOR THE CENTRAL COAST,
CLEARING TIMES MAY BE MORE OPTIMISTIC WITH SOME MODELS SHOWING
CLEARING LATER AROUND THE TIMEFRAME OF 20/21Z. A MORE TYPICAL MARINE
LAYER PATTERN WILL RETURN TONIGHT AS THE UPPER LEVEL LOW DEPARTS THE
BAY AREA. CURRENT THINKING IS THE MARINE LAYER WILL BE AROUND 2000
FT (FAVORING MVFR CIGS) AND OVERCAST CONDITIONS WILL RETURN LATE
OVERNIGHT. THE EXCEPTION IS ALONG THE COAST (HAF, MRY, SNS) WHERE
CONFIDENCE IS MODERATE TO HIGH THAT STRATUS WILL RETURN EARLY IN THE
EVENING.
VICINITY OF SFO...MVFR BECOMING VFR DURING THE AFTERNOON/EVENING
BEFORE MVFR CONDITIONS RETURN OVERNIGHT. CEILINGS ARE EXPECTED TO
CLEAR BY 19Z BUT LAMP GUIDANCE DOES SUGGEST CLEARING COULD BE
DELAYED TO 20Z. ONSHORE WINDS STRENGTHEN DURING THE
AFTERNOON/EVENING WITH GUSTS TO 21 KNOTS EXPECTED. ECMWF ENSEMBLE
GUIDANCE SHOWS SOME POTENTIAL FOR SLIGHTLY STRONGER GUSTS UP TO 25
KNOTS TO DEVELOP AT SFO TODAY. CONFIDENCE IN TIMING OF STRATUS
RETURN TONIGHT IS LOW TO MODERATE. CURRENTLY THINKING STRATUS WILL
RETURN CLOSER TO 09Z BUT THERE IS SOME POTENTIAL FOR IT TO RETURN AS
EARLY AS 06Z.
SFO BRIDGE APPROACH...SIMILAR TO SFO.
MONTEREY BAY TERMINALS...MVFR CONDITIONS CONTINUE THROUGH LATE
MORNING BEFORE A BRIEF PERIOD OF VFR CONDITIONS THIS AFTERNOON.
HIGHEST CONFIDENCE IN STRATUS CLEARING BY 18/19Z BUT THIS MAY BE ON
THE MORE OPTIMISTIC SIDE WITH SOME ENSEMBLE MEMBERS INDICATING
CLEARING BY 20/21Z. MVFR CIGS RETURN LATE THIS AFTERNOON/EARLY THIS
EVENING WITH CEILINGS TO GRADUALLY LOWER TO IFR OVERNIGHT. MODERATE
CONFIDENCE IN TIMING OF TRANSITION FROM MVFR TO IFR OVERNIGHT
TONIGHT.
MARINE
(TODAY THROUGH TUESDAY)
ISSUED AT 834 AM PDT THU SEP 11 2025
NORTHWEST WINDS INCREASE BEGINNING THURSDAY, BECOMING MODERATE TO
FRESH ACROSS THE MAJORITY OF THE COASTAL WATERS. LOCALIZED STRONG
GUSTS ARE POSSIBLE ACROSS THE NORTHERN OUTER WATERS. MODERATE TO
ROUGH SEAS DEVELOP FRIDAY AND PERSIST INTO NEXT WEEK. CONDITIONS
TEMPORARILY IMPROVE SATURDAY, AS WINDS DECREASE AND SEAS EASE,
BEFORE ANOTHER ROUND OF FRESH TO STRONG NW WINDS RETURNS SUNDAY
INTO NEXT WEEK WITH THE STRONGEST WINDS LOCATED ACROSS THE FAR
NORTHERN OUTER 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.
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 3 PM THIS AFTERNOON TO 3 AM PDT
SATURDAY FOR PT ARENA TO PT REYES 10-60 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...KENNEDY
MARINE...RGASS
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