210
FXUS66 KMTR 172135
AFDMTR
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SAN FRANCISCO CA
235 PM PDT WED SEP 17 2025
..NEW SHORT TERM, LONG TERM
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
(18Z TAFS)
ISSUED AT 1111 AM PDT WED SEP 17 2025
SATELLITE IMAGERY AND SURFACE OBSERVATIONS SHOW COASTAL STRATUS /IFR/
OTHERWISE IT'S VFR. THE MARINE LAYER IS CURRENTLY A FEW HUNDRED FEET
TO 1,000 FEET DEEP. INCOMING MID TO UPPER LEVEL HUMIDITY TODAY, TONIGHT
AND THURSDAY WILL DISRUPT RADIATIVE PROCESSES, LIKELY DISRUPTING THE
MARINE LAYER CLOUDS AND FOG, BUT IT'S UNKNOWN AS TO WHAT EXTENT. NEED
TO MONITOR THE PRECIPITABLE WATER (TROPICAL ORIGIN AIR MASS) REACHING
OUR AREA AND ITS POTENTIAL TO MERGE E.G. WITH 700 MB TO 500 MB CYCLONIC
FLOW AND WARM AIR/COLD AIR TEMPERATURE ADVECTION WHICH MAY RESULT IN
HYBRID LOW PRESSURE DEVELOPMENT; RARE IN AUG, SEP, BUT NOT UNPRECEDENTED.
VICINITY OF SFO...VFR. WEST WIND NEAR 10 KNOTS INCREASING TO 12 TO
22 KNOTS DURING THE AFTERNOON AND EARLY EVENING, DECREASING TO 5
TO 10 KNOTS TONIGHT AND THURSDAY MORNING.
SFO BRIDGE APPROACH...SIMILAR TO SFO.
MONTEREY BAY TERMINALS...COASTAL STRATUS CONTINUES TO MIX OUT WITH
VFR FORECAST FOR THE REMAINDER OF THE LATE MORNING AND AFTERNOON.
LOW TO VERY LOW CONFIDENCE IN THE FORECAST TONIGHT AND THURSDAY
MORNING SINCE MID TO UPPER LEVEL HUMIDITY WILL INCREASE LIKELY
RESULTING IN A DISRUPTION TO THE MARINE LAYER STRATUS AND FOG, BUT
TO WHAT EXTENT IS UNKNOWN. 18Z TAFS CURRENTLY ADVERTISE IFR, BUT
IT'S A LOW TO VERY LOW CONFIDENCE FORECAST. OTHERWISE MAINLY ONSHORE
WINDS 5 TO 10 KNOTS EXCEPT TEMPORARILY LIGHT EAST TO SOUTHEAST WINDS
LATE TONIGHT AND THURSDAY MORNING.
MARINE
(TODAY THROUGH MONDAY)
ISSUED AT 1040 AM PDT WED SEP 17 2025
EXPECT HAZARDOUS CONDITIONS OVER THE OUTER WATERS THROUGH FRIDAY
DUE TO STRONG NORTHERLY BREEZES AND ROUGH SEAS THAT ARE DEVELOPING
TODAY. GALE FORCE GUSTS AND VERY ROUGH SEAS ARE LIKELY IN THE
NORTHERN OUTER WATERS. THERE'S A SLIGHT CHANCE OF THUNDERSTORMS
TODAY AND TOMORROW, POSING THE RISKS 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...SMALL CRAFT ADVISORY UNTIL 3 PM PDT THIS AFTERNOON FOR PT ARENA
TO PT REYES 10-60 NM.
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/JM
LONG TERM....RGASS
AVIATION...CANEPA
MARINE...CANEPA
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