789
FXUS66 KMTR 151225
AFDMTR
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SAN FRANCISCO CA
525 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.
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
(12Z TAFS)
ISSUED AT 524 AM PDT FRI AUG 15 2025
MVFR CIGS ARE AFFECTING HAF AND THE MONTEREY BAY TERMINALS. CIGS
LOOK TO LAST INTO THE MID TO LATE MORNING AROUND THE MONTEREY BAY,
BUT LAST THROUGH THE TAF PERIOD FOR HAF. WINDS LOOK TO STAY LIGHT TO
MODERATE THROUGH THE MORNING AND INCREASE INTO LATE THE LATE MORNING
AND AFTERNOON, BECOMING BREEZY TO GUSTY. EXPECT THESE WINDS TO
REDUCE INTO EVENING BUT STAY MODERATE INTO THE NIGHT. WINDS ALOFT
WILL STAY ELEVATED IN THE EAST BAY, BUT FAIL TO REACH LLWS CRITERIA.
CIGS BUILD AGAIN ALONG THE COAST AND MONTEREY BAY INTO THE EVENING
AND PUSH INLAND INTO THE NIGHT, OFFERING MVFR/IFR CIGS FOR ALL BUT
THE NORTH BAY SITES. CIGS FALL TO LIFR LEVEL ALONG THE IMMEDIATE
COAST AND AT HAF INTO THE LATE NIGHT.
VICINITY OF SFO...VFR LASTS INTO THE NIGHT. WINDS STAY LIGHT THROUGH
THE LATE MORNING BEFORE BECOMING MORE MODERATE, THEN BECOMING
STRONG AND GUSTY FOR THE AFTERNOON. GUSTS ARE EXPECTED TO PEAK
ABOVE 30 KTS THROUGH THE AFTERNOON AND EVENING BEFORE REDUCING
INTO THE NIGHT. WINDS STILL STAY BREEZY THROUGH THE NIGHT AND
SATURDAY MORNING, WITH IFR CIGS BUILDING INTO THE NIGHT AND
LASTING INTO SATURDAY AFTERNOON.
SFO BRIDGE APPROACH...SIMILAR TO SFO.
MONTEREY BAY TERMINALS...MVFR CIGS WITH LIGHT WINDS LAST INTO THE
LATE MORNING. WINDS BECOME MODERATE AND BREEZY INTO THE LATE MORNING
AND EARLY AFTERNOON AS CIGS ERODE OVER THE TERMINALS, BUT EXPECT
CLOUD COVER TO LINGER OVER THE MONTEREY BAY. WINDS WEAKEN AGAIN INTO
THE EVENING WITH MVFR CIGS MOVING OVER THE TERMINALS. MIST AND
DRIZZLE BUILD AROUND THE BAY LATER INTO THE NIGHT WITH CIGS FALLING
TO IFR LEVELS.
MARINE
(TODAY THROUGH WEDNESDAY)
ISSUED AT 524 AM PDT FRI AUG 15 2025
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 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 FROM 9 AM THIS MORNING TO 3 AM PDT SATURDAY FOR
PIGEON PT TO PT PINOS 0-10 NM.
SMALL CRAFT ADVISORY UNTIL 9 AM PDT THIS MORNING FOR PT PINOS TO
PT PIEDRAS BLANCAS 0-10 NM.
GALE WARNING FROM 9 AM THIS MORNING TO 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.
SHORT TERM...FLYNN
LONG TERM....FLYNN
AVIATION...MURDOCK
MARINE...MURDOCK
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