988
FXUS66 KMTR 180003
AFDMTR
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SAN FRANCISCO CA
503 PM PDT WED SEP 17 2025
..NEW AVIATION, MARINE
KEY MESSAGES
UPDATED AT 232 PM PDT WED SEP 17 2025
- SHOWERS WITH ISOLATED TO SCATTERED THUNDERSTORMS AS EARLY AS
LATE TONIGHT THROUGH FRIDAY
- COOLER AFTERNOON TEMPERATURES THROUGH LATE WEEK
- SLIGHT WARM UP FOR THE WEEKEND
SHORT TERM
ISSUED AT 232 PM PDT WED SEP 17 2025
(THIS EVENING THROUGH THURSDAY)
UPPER LEVEL MOISTURE IS STARTING TO SPREAD ACROSS THE CENTRAL COAST
THIS AFTERNOON AS REMNANTS OF MARIO HAS ARRIVED. THERE HAVE BEEN
SHOWERS AND ISOLATED THUNDERSTORMS SOUTH OF THE REGION EARLIER THIS
MORNING AND RAIN SHOWERS ALONG AND OFF OF THE BIG SUR COAST EARLY
THIS AFTERNOON. TONIGHT INTO THURSDAY MORNING THE POTENTIAL
INCREASES FOR ISOLATED TO SCATTERED RAIN SHOWERS AND ISOLATED
THUNDERSTORMS AS DEEPER MOISTURE MOVES NORTHWARD FROM THE SOUTH.
PRECIPITABLE WATER VALUES ARE FORECAST TO REACH FROM 1.00"-1.40"
ACROSS JUST ABOUT ALL OF THE REGION AS WE HEAD INTO THURSDAY
MORNING. THUS, THE POTENTIAL FOR DRY LIGHTNING ALMOST ENDS ENTIRELY!
HOWEVER, MUCAPE AND LAPSE RATES DO INCREASE THROUGH THE DAY THURSDAY
SUGGESTING THE THREAT FOR EMBEDDED THUNDERSTORMS REMAIN. CAMS
(CONVECTIVE-ALLOWING MODELS) ALSO SUPPORTS THIS.
FROM PREVIOUS FORECASTER: "ANY THUNDERSTORM ACTIVITY EARLY THURSDAY
MORNING IS EXPECTED TO REMAIN MOSTLY OFFSHORE, BUT THINGS GET MORE
INTERESTING BY LATE MORNING INTO THURSDAY AFTERNOON AS THE
ENVIRONMENT BECOMES MORE FAVORABLE FOR SCATTERED THUNDERSTORMS TO
DEVELOP ACROSS THE CENTRAL COAST INTO THE SOUTH BAY. GIVEN THE NEAR
RECORD PWATS, MUCAPE VALUES BETWEEN 200-400 J/KG, MODERATE PVA, AND
BULK SHEAR UP TO 30KTS BY EARLY THURSDAY AFTERNOON, A FEW STRONG
THUNDERSTORMS CAN'T BE RULED OUT ESPECIALLY ALONG THE SANTA LUCIA
AND THE BIG SUR COASTLINE WHERE TERRAIN COULD ALSO ENHANCE LIFT AT
TIMES NEAR THE SURFACE. THE PRIMARY CONCERN WOULD BE STRONG WIND
GUSTS UP TO 50 MPH, CLOUD-TO-GROUND LIGHTNING AND BRIEF DOWNPOURS
GIVEN THE HIGH PWATS THROUGH EARLY THURSDAY EVENING."
AFTERNOON TEMPERATURES ON THURSDAY WILL COOL TO NEAR OR SLIGHTLY
BELOW SEASONAL AVERAGES AS A RESULT OF THE INCREASED CLOUD COVER AND
THE APPROACHING TROUGH.
LONG TERM
ISSUED AT 232 PM PDT WED SEP 17 2025
(THURSDAY NIGHT THROUGH NEXT TUESDAY)
ISOLATED TO SCATTERED RAIN SHOWERS WILL LINGER INTO FRIDAY LATE
AFTERNOON OR EARLY EVENING BEFORE THE DEEPER MOISTURE SHIFTS
EASTWARD IN RESPONSE TO AN UPPER LEVEL TROUGH APPROACHING THE COAST.
SATURDAY WILL REMAIN SLIGHTLY BELOW SEASONAL AVERAGES AS FAR AS
TEMPERATURES GO. TEMPERATURES WARM BY SUNDAY AND MONDAY TO ABOVE
AVERAGE AS A WEAK RIDGE OF HIGH PRESSURE BUILDS IN FROM THE EAST.
UNSETTLED WEATHER RETURNS BY MONDAY NIGHT AND WILL CONTINUE INTO
TUESDAY AS ANOTHER ROUND OF TROPICAL MOISTURE ADVECTS NORTHWARD.
CHANCES GENERALLY REMAIN BELOW 30%, BUT BE SURE TO CHECK BACK FOR
THE LATEST FORECAST INFORMATION.
AVIATION
(00Z TAFS)
ISSUED AT 503 PM PDT WED SEP 17 2025
CURRENTLY VFR AT ALL TAF SITES WITH LIFR-IFR EXPECTED ALONG THE
COAST. MODELS ARE MORE BULLISH THAT IFR-MVFR CONDITIONS WILL BE MORE
WIDESPREAD TONIGHT BUT FORECASTER CONFIDENCE IN THAT SCENARIO IS
LOW. CURRENT THINKING IS THAT THE INCOMING TROPICAL MOISTURE AND
APPROACHING SHOWERS WILL DISRUPT THE MARINE LAYER AND PREVENT
STRATUS FROM REALLY DEVELOPING/MOVING INLAND. FOR COASTAL AREAS, LOW
CONFIDENCE IN STRATUS FORECAST. THE SAME UNCERTAINTY OF APPROACHING
SHOWERS/TROPICAL MOISTURE WILL INFLUENCE THE POTENTIAL FOR LIFR-IFR
CIGS OVERNIGHT. CURRENTLY LEANING TOWARDS LIFR CIGS INITIALLY THAT
WILL GRADUALLY RISE OVERNIGHT TO IFR. SHOWERS AND THUNDERSTORMS
BECOME MORE LIKELY BEGINNING TOMORROW MORNING WITH TEMPORARILY
LOWERED CEILINGS AND VISIBILITIES EXPECTED IF SHOWERS MOVE OVER AN
AIRPORT. CURRENTLY CONFIDENCE IS LOW ON INCLUDING THUNDERSTORMS IN
THE TAF BUT WILL MONITOR AND AMEND AS NEEDED. THE TWO AIRPORTS MOST
LIKELY TO SEE THUNDERSTORM ACTIVITY WILL BE MRY AND SNS WITH
GUIDANCE INDICATING INCREASING POTENTIAL LATE THURSDAY AFTERNOON
INTO EARLY FRIDAY MORNING.
VICINITY OF SFO...VFR THROUGH THE TAF PERIOD. GUIDANCE INDICATES A
PERIOD FROM 12-16Z WHERE MVFR CONDITIONS ARE POSSIBLE AT SFO BUT
CONFIDENCE IS LOW IN THIS SCENARIO. APPROACHING SHOWERS AND TROPICAL
MOISTURE SHOULD DISRUPT THE MARINE LAYER AND KEEP CEILING BASES
HIGH. SHOWER ACTIVITY INCREASES EARLY THURSDAY MORNING AND WILL
CONTINUE THROUGH THE END OF THE TAF PERIOD. THUNDERSTORM POTENTIAL
CONTINUES FOR THURSDAY BUT CONFIDENCE IS NOT HIGH ENOUGH TO INCLUDE
IN TAF AT THIS TIME.
SFO BRIDGE APPROACH...SIMILAR TO SFO.
MONTEREY BAY TERMINALS...CURRENTLY VFR. SHOWERS ARE APPROACHING ON
RADAR WITH THUNDER OBSERVED OFFSHORE OF SOUTHERN MONTEREY COUNTY.
FORECASTER WILL KEEP AN EYE ON THESE SHOWERS AND AMEND FOR
THUNDERSTORMS AS NEEDED AS THEY MOVE FURTHER INTO THE COUNTY.
TEMPORARY DECREASES IN CEILING HEIGHT AND VISIBILITY ARE EXPECTED IF
A STRONGER SHOWER MOVES DIRECTLY OVER THE AIRPORT. LOW CONFIDENCE IN
CIG FORECAST FOR TONIGHT GIVEN APPROACHING SHOWERS AND TROPICAL
MOISTURE. CIGS INITIALLY START OUT AS LIFR BUT GRADUALLY BECOME IFR-
MVFR OVERNIGHT. SHOWER AND THUNDERSTORM ACTIVITY WILL INCREASE
HEADING INTO THURSDAY WITH GUIDANCE SUGGESTING A PARTICULARLY ACTIVE
PERIOD FOR MRY AND SNS THURSDAY AFTERNOON TO EARLY FRIDAY MORNING
(JUST BEYOND THIS TAF PERIOD).
MARINE
(TONIGHT THROUGH NEXT TUESDAY)
ISSUED AT 503 PM PDT WED SEP 17 2025
EXPECT HAZARDOUS CONDITIONS OVER THE OUTER WATERS THROUGH FRIDAY
DUE TO STRONG NORTHERLY BREEZES AND ROUGH SEAS. GALE FORCE GUSTS
AND VERY ROUGH SEAS ARE LIKELY IN THE NORTHERN OUTER WATERS.
THERE'S A SLIGHT CHANCE OF THUNDERSTORMS THROUGH TONIGHT AND
TOMORROW, POSING THE RISK OF GUSTY OUTFLOW WINDS, ROUGH SEAS AND
LOCALLY HEAVY RAINFALL. ISOLATED RAIN SHOWERS WILL LINGER THROUGH
FRIDAY.
FIRE WEATHER
ISSUED AT 945 AM PDT WED SEP 17 2025
- NEAR CRITICAL FIRE WEATHER CONDITIONS THROUGH TODAY
- THREAT FOR DRY LIGHTNING HAS DIMINISHED, BUT DIDN'T COMPLETELY GO
AWAY FROM EARLY THURSDAY MORNING THROUGH FRIDAY MORNING
NEAR CRITICAL FIRE WEATHER CONDITIONS CONTINUE THROUGH THIS EVENING
DUE TO HOT, DRY, AND AFTERNOON BREEZY ONSHORE WINDS. WHILE THE
THREAT FOR DRY LIGHTNING HAS DIMINISHED AS IT REMAINS OFFSHORE, ANY
LIGHTNING STRIKES WILL HAVE THE POTENTIAL FOR FIRE STARTS BEFORE WE
TRANSITION TO WETTING RAINS. THIS IS ESPECIALLY SO ACROSS THE
SOUTHERN AREAS OF THE CENTRAL COAST WHERE HIGHER ELEVATIONS REMAIN
DRY THROUGH THIS AFTERNOON AND EVENING.
THIS FORECAST IS LOW CONFIDENCE, YET HIGH IMPACT SCENARIO THROUGH
THIS AFTERNOON AND EVENING IF ANY FIRE STARTS WERE TO HAPPEN. THE
THREAT FOR DRY LIGHTNING GREATLY DIMINISHES LATE TONIGHT INTO
THURSDAY MORNING AS THE MOISTURE PROFILE DEEPENS AND WE TRANSITION
TO WETTING RAINS ON THURSDAY THROUGH FRIDAY MORNING. IF THE THREAT
SHIFTS EAST WE'LL HAVE TO RE-EVALUATE.
RGASS
MTR WATCHES/WARNINGS/ADVISORIES
CA...NONE.
PZ...GALE WARNING UNTIL 9 AM PDT THURSDAY FOR PT ARENA TO PT REYES 10-
60 NM.
SMALL CRAFT ADVISORY UNTIL 9 AM PDT THURSDAY FOR PIGEON PT TO PT
PINOS 10-60 NM.
SHORT TERM...RGASS
LONG TERM....RGASS
AVIATION...KENNEDY
MARINE...CANEPA
VISIT US AT WWW.WEATHER.GOV/SANFRANCISCO
FOLLOW US ON FACEBOOK, X, AND YOUTUBE AT:
WWW.FACEBOOK.COM/NWSBAYAREA
X.COM/NWSBAYAREA
WWW.YOUTUBE.COM/NWSBAYAREA
CLICK HERE TO GO TO PREVIOUS BULLETINS.
Main Text Page