156
FXUS66 KMTR 161747
AFDMTR
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SAN FRANCISCO CA
1047 AM PDT TUE SEP 16 2025
..NEW AVIATION, MARINE
KEY MESSAGES
UPDATED AT 412 AM PDT TUE SEP 16 2025
- DENSE FOG ADVISORY FOR PORTIONS OF THE CENTRAL COAST UNTIL 10AM
- ABOVE NORMAL TEMPERATURES WITH MODERATE HEATRISK PERSISTS TODAY
AND WEDNESDAY
- ISOLATED TO SCATTERED THUNDERSTORMS POSSIBLE THURSDAY INTO
EARLY FRIDAY
SHORT TERM
ISSUED AT 412 AM PDT TUE SEP 16 2025
(TODAY AND TONIGHT)
AREAS OF DENSE FOG HAVE DEVELOPED OVERNIGHT FROM THE SAN FRANCISCO
PENINSULA COAST SOUTH THROUGH SANTA CRUZ, MONTEREY BAY, THE SALINAS
VALLEY AND THE BIG SUR COASTLINE, WITH A DENSE FOG ADVISORY OUT
UNTIL 10AM. OTHERWISE WE'RE LOOKING AT ANOTHER DAY WITH TEMPERATURES
WELL ABOVE NORMAL AND WIDESPREAD MODERATE HEATRISK, EXPECT DAYTIME
HIGHS TODAY TO BE SLIGHTLY HIGHER THAN YESTERDAY. REMEMBER TO REMAIN
HYDRATED WITH PLENTY OF WATER AND ELECTROLYTES, LIMIT TIME OUTDOORS
DURING PEAK HEATING IF POSSIBLE, AND NEVER LEAVE CHILDREN OR PETS
UNATTENDED IN VEHICLES.
KEEPING WITH THE WARM TREND, OVERNIGHT LOWS INTO WEDNESDAY MORNING
WILL CONTINUE TO BE ABOVE NORMAL AS WELL, WITH SOME ELEVATED AREAS
IN THE BAY AREA, EAST BAY HILLS, DIABLO RANGE, AND SANTA LUCIAS
REMAINING IN THE 70S WITH POOR RH RECOVERY.
LONG TERM
ISSUED AT 412 AM PDT TUE SEP 16 2025
(WEDNESDAY THROUGH MONDAY)
WEDNESDAY WILL BE THE LAST DAY OF THE THREE DAY HEAT WAVE, WITH
TEMPERATURES SIMILAR TO TODAYS HIGHS AND WIDESPREAD MODERATE
HEATRISK. A PATTERN SHIFT FOR THURSDAY AND FRIDAY INTO THE WEEKEND
WILL CONTINUE TO BRING COOLER TEMPERATURES, RAINFALL CHANCES AND
ELEVATED THUNDERSTORM CHANCES. HOWEVER, THERE HAS BEEN A NOT SO
SUBTLE SHIFT IN GUIDANCE ACROSS THE BOARD IN THE MOST RECENT
UPDATES. ISOLATED TO SCATTERED THUNDERSTORMS REMAIN IN THE FORECAST
FOR NOW FROM THE BAY AREA SOUTH THROUGH THE CENTRAL COAST DURING THE
DAY THURSDAY INTO EARLY FRIDAY. THE UPPER LEVEL PATTERN HAS SHIFTED
QUITE A BIT FROM MONDAY AFTERNOONS FORECAST UPDATE TO THIS MORNING.
AN UNUSUAL SYNOPTIC PATTERN (A DOUBLE OMEGA BLOCK ACROSS CONUS?),
AGREED UPON IN NUMEROUS FORMS OF DETERMINISTIC GUIDANCE HAS THE
REMNANTS OF MARIO BECOMING THE MORE DOMINANT FEATURE AS IT LIFTS
NORTH INTO SOCAL. AS A RESULT, THE BULK OF RAINFALL AND
INSTABILITY HAS TAKEN A NOTABLE SHIFT EAST AND SOUTH AWAY FROM OUR
FORECAST AREA. THAT DOESN'T MEAN WE WON'T SEE ANY SHOWERS OR
THUNDERSTORMS OVER THE NEXT 72 HOURS, BUT CONFIDENCE IS LOWER THAN
IT WAS YESTERDAY AND THE TREND APPEARS TO BE DRIER. THERE IS TIME
FOR THE FORECAST TO WHIPLASH BACK TO WETTER AND MORE UNSTABLE FOR
OUR AREA, ESPECIALLY ACROSS THE CENTRAL COAST. BUT FOR NOW
(INCLUDING MOST RECENT 06Z GFS UPDATE, AND SLOWER NORTHERLY
PROGRESSION OF 06Z HRRR), IT APPEARS THAT MARIO GETS ABSORBED
INLAND ACROSS SOCAL UNDER THE NEGATIVELY TILTED RIDGE AXIS FROM SE
OREGON TO SOUTHERN ARIZONA. PWATS WILL STILL BE WELL ABOVE NORMAL
AND EVEN IF WE DON'T SEE ANY RAINFALL IT WILL FEEL MUGGY. WE
OFTEN SAY 'CHECK BACK FOR UPDATES', TODAY IS DEFINITELY ONE OF
THOSE DAYS.
AVIATION
(18Z TAFS)
ISSUED AT 1046 AM PDT TUE SEP 16 2025
VFR CONDITIONS HAVE RETURNED TO MOST SITES AWAY FROM THE IMMEDIATE
COAST WITH KHAF STILL SEEING LIFR CEILINGS/VISIBILITIES THAT SHOULD
SCATTERED OUT BY 22Z. ONSHORE WINDS WILL INCREASE THIS AFTERNOON
BEFORE EASING AFTER SUNSET AND MORE SO INTO WEDNESDAY MORNING. HIGH
CONFIDENCE OF VFR CONDITIONS PREVAILING THROUGH THE TAF PERIOD FOR
THE BAY AREA TERMINALS AND LIFR CONDITIONS FOR THE MONTEREY BAY
TERMINALS (AND KHAF).
VICINITY OF SFO...VFR. HIGH CONFIDENCE FOR ONSHORE WINDS TO INCREASE
THIS AFTERNOON BEFORE EASING INTO EARLY WEDNESDAY MORNING. HIGH
CONFIDENCE FOR VFR CONDITIONS TO PREVAIL THROUGH THE TAF PERIOD WITH
INCREASING ONSHORE WINDS ONCE AGAIN WEDNESDAY AFTERNOON.
SFO BRIDGE APPROACH...SIMILAR TO SFO.
MONTEREY BAY TERMINALS...VFR. ONSHORE WINDS INCREASE THIS AFTERNOON
BEFORE EASING AFTER SUNSET. HIGH CONFIDENCE FOR LIFR CONDITIONS TO
RETURN TO THE REGION LATE EVENING AND CONTINUE THROUGH ABOUT 16Z
WEDNESDAY.
MARINE
(TODAY THROUGH SUNDAY)
ISSUED AT 1046 AM PDT TUE SEP 16 2025
A GENTLE TO MODERATE NORTHERLY BREEZE WILL PREVAIL TODAY,
INCREASING TO BECOME FRESH TO STRONG FOR THE NORTHERN OUTER WATERS
WEDNESDAY NIGHT INTO THURSDAY. MODERATE SEAS WILL PREVAIL TODAY,
BUILDING TO BECOME ROUGH FOR THE OUTER WATERS WEDNESDAY THROUGH
FRIDAY. ISOLATED THUNDERSTORMS ARE POSSIBLE WEDNESDAY NIGHT AND
THURSDAY WITH ISOLATED RAIN SHOWERS LINGERING THROUGH SATURDAY.
FIRE WEATHER
ISSUED AT 624 AM PDT TUE SEP 16 2025
NEAR CRITICAL FIRE WEATHER CONDITIONS FOR TUESDAY THANKS TO HOT,
DRY, AND AFTERNOON BREEZY ONSHORE WINDS. TO START THE DAY ACTIVE
THERMAL BELTS IN PLACE WITH MILD AND DRY CONDITIONS OVER THE
HIGHER ELEVATIONS. OVERNIGHT HUMIDITY RECOVERY WAS MODERATE TO
POOR WITH THE HIGHEST PEAKS NOT EVEN REACHING 30% RH OVERNIGHT.
AMPLE SUNSHINE AND A WARM AIRMASS WILL YIELD TEMPERATURES WELL
INTO THE 90S AND LOW 100S ACROSS THE INTERIOR. COMPOUND THE HEAT
WITH LOW HUMIDITY THIS AFTERNOON IN THE TEENS TO 20% RANGE AND
TYPICAL GUSTS UP TO 20-25 MPH WILL RESULT IN NEAR CRITICAL FIRE
WEATHER CONDITIONS. THEREAFTER THE FORECAST FOCUS SHIFTS TO LOW
CONFIDENCE HIGH IMPACT SCENARIO AS TROPICAL MOISTURE BRINGS A
CHANCE FOR ELEVATED/HIGH-BASED THUNDERSTORMS. THE BIGGEST CONCERN
WILL BE THE CHANCE FOR DRY LIGHTNING WEDNESDAY INTO THURSDAY,
WHICH COMES ON THE HEELS OF A FEW DAYS OF HOT/DRY ACROSS THE
INTERIOR. WE'LL CONTINUE TO ASSESS THE SITUATION AND COORDINATE
WITH FIRE PARTNERS TUESDAY MORNING BEFORE MAKING ANY DECISIONS
REGARDING ANY FIRE WATCHES.
MM
MTR WATCHES/WARNINGS/ADVISORIES
CA...NONE.
PZ...NONE.
SHORT TERM...JM
LONG TERM....JM
AVIATION...RGASS
MARINE...RGASS
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