602
FXUS66 KMTR 171811
AFDMTR
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SAN FRANCISCO CA
1111 AM PDT WED SEP 17 2025
..NEW AVIATION, MARINE
KEY MESSAGES
UPDATED AT 945 AM PDT WED SEP 17 2025
- ABOVE NORMAL TEMPERATURES WITH WIDESPREAD MODERATE HEATRISK
ACROSS THE INTERIOR TODAY
- SHOWERS WITH ISOLATED TO SCATTERED THUNDERSTORMS AS EARLY AS
LATE TONIGHT THROUGH FRIDAY
UPDATE
ISSUED AT 945 AM PDT WED SEP 17 2025
THE DENSE FOG ADVISORY WILL BE ALLOWED TO EXPIRE AT 10 AM AS
VISIBILITIES CONTINUE TO IMPROVE ALONG COASTAL LOCATIONS.
THAT SAID, KEEPING AN EYE ON CONVECTION OVER SAN LUIS OBISPO
COUNTY THIS MORNING, WHICH HAS THE POTENTIAL TO MOVE INTO MONTEREY
COUNTY LATER THIS MORNING AND INTO THE AFTERNOON. HOWEVER,
PROBABILITIES REMAIN LESS THAN 20%. HAVE ADDED A SLIGHT CHANCE OF
SHOWERS AND THUNDERSTORMS TO THE OFFICIAL FORECAST THROUGH 00Z
THURSDAY FOR THE FAR SOUTHERN PORTIONS OF MONTEREY COUNTY.
OTHERWISE, THE FORECAST REMAIN ON TRACK AND WILL BE UPDATING THE
FIRE WEATHER SECTION BELOW.
RGASS
SHORT TERM
ISSUED AT 406 AM PDT WED SEP 17 2025
(TODAY AND TONIGHT)
AREAS OF DENSE FOG HAVE DEVELOPED ACROSS THE PACIFIC COAST AND THE
WATERS OF MONTEREY BAY WITH A DENSE FOG ADVISORY IN EFFECT UNTIL
10AM ONCE AGAIN THIS MORNING.
THERMAL BELTS REMAIN ACTIVE WITH A MAJORITY OF SITES ABOVE 1500FT AT
70 DEGREES OR HIGHER AND RH VALUES MOSTLY BETWEEN 25%-40%, WITH OAK
RIDGE THE LOWEST AT 16% AS OF 3AM. AS WE WARM TO ABOVE NORMAL
TEMPERATURES FOR THE LAST DAY OF THIS RELATIVELY SHORT HEAT WAVE,
WE'LL ALSO BE KEEPING AN EYE ON THE TROPICAL PLUME OF MOISTURE
WORKING ITS WAY NORTH FROM SOCAL. VANDENBERG RADAR IS PICKING UP
AN AREA OF ELEVATED SHOWERS OVER THE OPEN WATER MOVING DUE NORTH
PAST THE CHANNEL ISLANDS AND POINT CONCEPTION AT THIS HOUR, WHICH
MAY BE A LITTLE AHEAD OF SCHEDULE WITH A NUMBER OF INDIVIDUAL
HIRES CAMS SEEMING TO PICK UP ON THE GENERAL ACTIVITY SO FAR. THE
BULK OF THE FIRST WAVE OF SHOWER ACTIVITY AND ISOLATED
THUNDERSTORMS IS EXPECTED TO REMAIN OFFSHORE AS IT WORKS NORTH
TOWARD OUR LATITUDE LATER TODAY AND TONIGHT. BY LATE TONIGHT INTO
THE EARLY HOURS OF THURSDAY MORNING WE SEE INCREASING CHANCES OF
SHOWERS AND ISOLATED THUNDERSTORMS MOVING INTO SOUTHERN MONTEREY
COUNTY AND SAN BENITO COUNTY. THERE IS STILL A SLIGHT CHANCE OF
DRY THUNDERSTORM ACTIVITY AND LIGHTNING INITIALLY AS THE ACTIVITY
MOVES INTO OUR AREA LATE TONIGHT, BUT WE QUICKLY SHIFT TOWARD MORE
WETTING RAINFALL WITH ENSEMBLE MEAN PWATS INDICATING AROUND
1.40", ASSOCIATED WITH THE LEADING EDGE OF THE REMNANTS OF MARIO
OVER OUR SOUTHERN ZONES BY SUNRISE THURSDAY MORNING. THAT MEAN
VALUE IS 200% OF NORMAL, GIVING HIGH CONFIDENCE THAT WE'LL SEE
NEAR RECORD PWATS WITH THIS EVENT FOR THIS TIME OF THE YEAR.
LONG TERM
ISSUED AT 406 AM PDT WED SEP 17 2025
(THURSDAY THROUGH TUESDAY)
AS MENTIONED ABOVE, THE LEADING EDGE OF THE REMNANTS OF MARIO MOVE
INTO OUR AREA BY EARLY THURSDAY MORNING. 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. THUNDERSTORM ACTIVITY IS EXPECTED TO
GRADUALLY DECLINE AFTER SUNSET WITH SCATTERED SHOWER ACTIVITY
PERSISTING THROUGH THE OVERNIGHT INTO FRIDAY AS THE CENTER OF THE
REMNANTS OF MARIO SHIFTS INTO NORCAL. WEAK RIDGING BUILDS NORTH
OUT OF THE DESERT SOUTHWEST FOR THE WEEKEND, AS ANOTHER WEAK
DISTURBANCE APPROACHES THE WEST COAST FOR THE BEGINNING OF NEXT
WEEK. RAIN CHANCES INCREASE ONCE AGAIN MONDAY AFTERNOON AND
PERSIST INTO TUESDAY.
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 FROM 3 PM THIS AFTERNOON TO 9 AM PDT THURSDAY FOR
PT ARENA TO PT REYES 10-60 NM.
SMALL CRAFT ADVISORY FROM 3 PM THIS AFTERNOON TO 9 AM PDT
THURSDAY FOR PIGEON PT TO PT PINOS 10-60 NM.
SHORT TERM...JM
LONG TERM....JM
AVIATION...CANEPA
MARINE...CANEPA
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