204
FXUS66 KMTR 151748
AFDMTR
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SAN FRANCISCO CA
1048 AM PDT FRI AUG 15 2025
..NEW AVIATION, MARINE
KEY MESSAGES
UPDATED AT 1211 AM PDT FRI AUG 15 2025
- STRONG NW WINDS THROUGH SATURDAY NIGHT.
- MODERATE HEATRISK TODAY IN PORTIONS OF THE INTERIOR NORTH AND
EAST BAY.
- TEMPERATURES WILL COOL THIS WEEKEND.
UPDATE
ISSUED AT 1000 AM PDT FRI AUG 15 2025
MORNING VISIBLE SATELLITE PAINTS A DIFFERENT PICTURE THIS MORNING
THAN 24 HOURS AGO. MUCH LESS CLOUD COVER OVER THE NORTH AND EAST
BAY, INCLUDING THE NORTH BAY COAST. DRIER AIR MIXING IN AND A
DECENT N-S GRADIENT ARE CULPRITS. THE BIGGER IMPACT IN THE NEAR
TERM CONTINUES TO BE INCREASING WINDS THIS AFTERNOON AND EVENING.
IF YOU'RE HEADING TO THE BEACH, PLANNING AFTERNOON HIKE, OR JUST
PLAIN HANGING OUT OUTSIDE AT YOUR HOUSE, WINDS WILL INCREASE THIS
AFTERNOON AND PEAK LATE AFTERNOON/EVENING. WINDS WILL BE STRONGEST
ALONG THE COAST AND OUR FAVORED INLAND SPOTS LIKE THE EAST BAY
GAP/PASSES. GUSTS IN THE 30-40 MPH RANGE ARE POSSIBLE...BUT THERE
IS A 40-50% CHC AT SEEING SOME GUSTS OVER 40 MPH.
NO UPDATE PLANNED.
SHORT TERM
ISSUED AT 1211 AM PDT FRI AUG 15 2025
(TODAY AND TONIGHT)
THE MARINE LAYER HAS COMPRESSED OVER THE LAST 24 HOURS AND DRY AIR
HAS INTRUDED INTO THE LESS STRATIFIED BOUNDARY LAYER. THE 24 HOUR
RH CHANGE SHOWS ANYWHERE FROM 5-15% DRIER CONDITIONS ACROSS THE
CWA. THE GOES WEST NIGHT FOG PRODUCT SHOWS CLEAR SKIES ACROSS THE
NORTH AND EAST BAY, WITH A MUCH SMALLER AREA OF STRATUS CONFINED
TO THE SF PENINSULA COAST AND MONTEREY BAY REGION. THIS CHANGE IS
CAUSED BY BUILDING SURFACE HIGH PRESSURE OVER FAR NW CALIFORNIA.
THE SFO-ACV GRADIENT HAS INCREASED FROM -2.1 MB TO -5.9 MB OVER
THE LAST 24 HOURS. WHILE THE HIGH PRESSURE HAS WORKED TO COMPRESS
THE MARINE LAYER (PARTICULARLY IN THE NORTH BAY), THE PRESSURE
GRADIENT HAS GENERATED STRONG NNW WINDS THAT ARE MECHANICALLY
MIXING MUCH DRIER AIR ALOFT INTO THE MARINE LAYER. THE CLEAR SKIES
WILL BRING WARMER TEMPERATURES THIS AFTERNOON DUE TO ENHANCED
INSOLATION. THE MONTEREY BAY REGION IS FAR ENOUGH SOUTH TO BE
PROTECTED FROM THIS CHANGE. THE FT. ORD PROFILER SHOWS THE MARINE
LAYER IS MAINTAINING AROUND 2,000 FEET DEEP WHILE THE LATEST
SOUNDING FROM OAKLAND FOUND IT TO BE ROUGHLY 850 FEET DEEP IN THE
BAY AREA. AS THE SACRAMENTO VALLEY WARMS INTO THE 90S AND THE
TYPICAL DIURNAL W-E GRADIENT BUILDS THIS AFTERNOON, THE
COMBINATION OF THE TWO GRADIENTS WILL SUPPORT STRONG NW WINDS
THROUGH THE AFTERNOON AND EVENING. GUSTS ARE EXPECTED TO REACH AS
HIGH AS 40 MPH ALONG THE COAST AND IN HIGHER TERRAIN.
LONG TERM
ISSUED AT 1211 AM PDT FRI AUG 15 2025
(SATURDAY THROUGH THURSDAY)
A STRONG LOW PRESSURE SYSTEM IS CURRENTLY BRINGING AN UNUSUAL
AMOUNT OF RAIN TO THE PACIFIC NORTHWEST FOR THIS TIME OF YEAR. BY
SATURDAY A ROBUST PLUME OF MOISTURE ASSOCIATED WITH THIS SYSTEM
WILL MOVE OVER THE BAY AREA. MOST MODEL GUIDANCE AGREES THIS WILL
BRING THE PW TO NEAR 1.5" BY 18Z. THIS IS WELL ABOVE THE 90TH
PERCENTILE FOR THIS TIME OF YEAR (1.04"). WITH SUCH HIGH
ATMOSPHERIC MOISTURE, WE HAVE TO CONSIDER THE POSSIBILITY OF RAIN
OR CONVECTION. THE EXPERIMENTAL 3KM RRFS SHOWS 567 J/KG OF CAPE
ABOVE SANTA ROSA AT 21Z ON SATURDAY, AND THE 06Z HRRR RUN IS OVER
800 J/KG. THE CAPE PROFILE IS VERY LONG AND SKINNY HOWEVER, WHICH
MEANS IT'S HIGHLY SENSITIVE TO SMALL CHANGES IN SURFACE
TEMPERATURE. FOR EXAMPLE THE ECMWF SHOWS 0 CAPE AT THE SAME TIME
MAINLY BECAUSE THE SIMULATED SURFACE TEMPERATURE IS A FEW DEGREES
COOLER. SINCE THIS CAPE IS SURFACE BASED, THERE IS REALLY NO
CHANCE FOR CONVECTION TO POP-UP ANYWHERE ABOVE COASTAL LOCATIONS
STUCK IN THE MARINE LAYER. THE NBM DOES BRING A 1-3% CHANCE OF
THUNDERSTORMS TO THE INTERIOR NORTH BAY, WHICH MAKES SENSE DUE TO
THE SMALL WINDOW OF INSTABILITY BEFORE THE SUN STARTS TO GO DOWN.
MOST LIKELY NOTHING WILL HAPPEN, BUT THERE IS A CHANCE FOR CUMULUS
CLOUDS, SLIGHT CHANCE FOR RAIN SHOWERS, AND AN OUTSIDE
POSSIBILITY FOR A THUNDERSTORM IN THE NORTH BAY SATURDAY.
OTHERWISE THE STRONG WINDS DESCRIBED IN THE SHORT TERM SECTION
WILL PERSIST THROUGH SATURDAY, PARTICULARLY IN THE AFTERNOON.
CLOUD COVER WILL REBUILD SATURDAY NIGHT AS THE WINDS DECREASE AND
MARINE LAYER RETURNS TO FORM BY SUNDAY MORNING. THE REST OF THE
WEEK WILL FEATURE A GRADUAL WARMING TREND AS HIGH PRESSURE OVER
THE 4 CORNERS GRADUALLY NUDGES THE EAST PACIFIC TROUGH FURTHER
OFFSHORE. THE CURRENT FORECAST BRINGS MID 90S BACK TO THE WARMER
AREAS BY THE END OF THE WORK-WEEK.
AVIATION
(18Z TAFS)
ISSUED AT 1046 AM PDT FRI AUG 15 2025
VFR CONDITIONS ARE RETURNING TO SITES THAT HAD BEEN MVFR EARLIER
THIS MORNING WITH ALL SITES EXPECT FOR HAF WHERE IFR/MVFR CONDITIONS
MAY PERSIST THROUGH MUCH OF THE TAF PERIOD. A MODERATE TO STRONG
WESTERLY TO NORTHWESTERLY BREEZE WILL CONTINUE TO INCREASE THROUGH
THE AFTERNOON AND GRADUALLY DIMINISH INTO EARLY SATURDAY MORNING.
THERE IS HIGH CONFIDENCE FOR IFR/MVFR CONDITIONS TO RETURN TO THE
MONTEREY BAY TERMINALS THIS EVENING WITH MODERATE TO HIGH CONFIDENCE
FOR MVFR CONDITIONS RETURNING EARLY SATURDAY MORNING AROUND THE BAY
AREA TERMINALS (POTENTIALLY LOWERING TO IFR).
VICINITY OF SFO...VFR. ONSHORE WINDS WILL INCREASE THIS AFTERNOON
WITH GUSTS AT SFO GREATER THAN 35KT THROUGH ABOUT 05Z SATURDAY.
MODERATE TO HIGH CONFIDENCE FOR MVFR CEILINGS TO RETURN EARLY
SATURDAY MORNING WITH THE POTENTIAL TO LOWER TO IFR AROUND SUNRISE.
LOW CLOUDS WILL LIFT LATE SATURDAY MORNING AND POTENTIALLY LINGER
THROUGH ABOUT 20Z SATURDAY. WINDS ARE FORECAST TO BE WEAKER SATURDAY
AFTERNOON, YET GUSTY CONDITIONS WILL BE LIKELY.
SFO BRIDGE APPROACH...LOW CEILINGS ARE ANTICIPATED TO SCATTER OUT
SOONER ON SATURDAY MORNING OVER THE APPROACH. OTHERWISE, SIMILAR TO
SFO.
MONTEREY BAY TERMINALS...VFR. ONSHORE WINDS INCREASE THIS AFTERNOON
WITH GUSTY CONDITIONS THROUGH THIS EVENING BEFORE WINDS DIMINISH
AFTER SUNSET. HIGH CONFIDENCE FOR AN EARLY RETURN OF MVFR CEILINGS
THAT WILL THEN LOWER TO IFR EARLY SATURDAY MORNING.
MARINE
(TODAY THROUGH WEDNESDAY)
ISSUED AT 1046 AM PDT FRI AUG 15 2025
NORTHWESTERLY GALE FORCE GUSTS ARE BUILDING ACROSS MUCH THE
WATERS AND LOOK TO LAST INTO LATE SATURDAY NIGHT. THE BAYS WILL
EXPERIENCE HAZARDOUS CONDITIONS FRIDAY AND SATURDAY DUE TO FRESH
TO STRONG WESTERLY BREEZES WITH NEAR-GALE FORCE GUSTS. BREEZES
WILL SLOWLY DIMINISH BY LATE WEEKEND WITH ADDITIONAL EASING
OCCURING EARLY NEXT WEEK. MODERATE TO ROUGH SEAS WILL PREVAIL
THROUGH SATURDAY FOR THE INNER WATERS AND OUTER WATERS WITH
MODERATE SEAS BY SUNDAY.
MTR WATCHES/WARNINGS/ADVISORIES
CA...NONE.
PZ...SMALL CRAFT ADVISORY FROM 3 PM THIS AFTERNOON TO 9 PM PDT
SATURDAY FOR SF BAY N OF BAY BRIDGE.
SMALL CRAFT ADVISORY FROM 3 PM THIS AFTERNOON TO 3 AM PDT
SATURDAY FOR MRY BAY.
SMALL CRAFT ADVISORY FROM 9 AM TO 9 PM PDT SATURDAY FOR MRY BAY.
GALE WARNING UNTIL 3 AM PDT SATURDAY FOR PIGEON PT TO PT PINOS 0-
10 NM-PT ARENA TO PT REYES 0-10 NM-PT ARENA TO PT REYES 10-
60 NM.
SMALL CRAFT ADVISORY UNTIL 3 PM PDT THIS AFTERNOON FOR PT REYES
TO PIGEON PT 0-10 NM.
GALE WARNING FROM 3 PM THIS AFTERNOON TO 3 AM PDT SATURDAY FOR
PT REYES TO PIGEON PT 0-10 NM.
GALE WARNING UNTIL 9 AM PDT SATURDAY FOR PT PINOS TO PT PIEDRAS
BLANCAS 0-10 NM.
GALE WARNING UNTIL 3 PM PDT THIS AFTERNOON FOR PIGEON PT TO PT
PINOS 10-60 NM.
UPDATE...MM
SHORT TERM...FLYNN
LONG TERM....FLYNN
AVIATION...RGASS
MARINE...RGASS
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