137
FXUS66 KMTR 031212
AFDMTR
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SAN FRANCISCO CA
512 AM PDT SAT OCT 3 2026
..NEW AVIATION, MARINE, FIRE WEATHER
KEY MESSAGES
UPDATED AT 1243 AM PDT SAT OCT 3 2026
- MODERATE TO MAJOR HEATRISK ACROSS THE BAY AREA AND CENTRAL
COAST SATURDAY AND SUNDAY
- MODERATE TO MAJOR HEATRISK ACROSS THE INTERIOR BAY AREA AND
CENTRAL COAST MONDAY THROUGH THURSDAY
- ELEVATED FIRE WEATHER CONDITIONS ACROSS THE HIGHER TERRAIN
THROUGH THURSDAY
SHORT TERM
ISSUED AT 1243 AM PDT SAT OCT 3 2026
(SATURDAY AND SUNDAY)
THE 00Z SOUNDING OBSERVED AN 850 MB TEMPERATURE OF 22.95 DEGREES
CELSIUS AND A 500 MB HEIGHT OF 5900 METERS, BOTH OF THESE ARE ABOVE
THE 90TH PERCENTILE. THE HEAT WILL PEAK THIS WEEKEND AS AN UPPER-
LEVEL LONGWAVE RIDGE DRIFTS IN FROM THE EASTERN PACIFIC OCEAN. A
HEAT ADVISORY WILL GO INTO EFFECT AT 11 AM SATURDAY AND RUN THROUGH
10 PM SUNDAY FOR MOST OF THE BAY AREA AND CENTRAL COAST. IT WAS
EXTENDED IN AREA TO INCLUDE THE CARMEL VALLEY, HOLLISTER VALLEY,
MARIN COASTAL RANGE, NORTHERN MONTEREY BAY, NORTHERN SALINAS VALLEY,
AND SAN FRANCISCO. NOW, THE ONLY PLACES THAT ARE NOT INCLUDED IS THE
NORTH BAY COAST, SAN FRANCISCO PENINSULA COAST, AND SOUTHERN
MONTEREY BAY; THIS IS BANKING ON A COMPRESSED MARINE LAYER KEEPING
THESE SPOTS COOL. IF THE COMPRESSED MARINE LAYER IS ABLE TO SURVIVE,
EXPECT REDUCED VISIBILITY FROM FOG ALONG THE COAST. IF IT IS NOT
ABLE TO SURVIVE, COASTAL CONDITIONS WILL BE HOTTER THAN CURRENTLY
FORECAST. MODERATE TO MAJOR HEATRISK WILL RESULT FROM MAXIMUM
TEMPERATURES 10 TO 20 DEGREES ABOVE NORMAL. MINIMUM TEMPERATURES 10
TO 20 DEGREES ABOVE NORMAL WITH WEAKER THAN NORMAL ONSHORE FLOW WILL
BRING LIMITED RELIEF OVERNIGHT, ALSO CONTRIBUTING TO HEATRISK. EVEN
LESS RELIEF IS EXPECTED IN THE HIGHER TERRAIN WHERE ELEVATED FIRE
WEATHER CONDITIONS CONTINUE WITH HOT AND DRY CONDITIONS, PROMINENT
THERMAL BELTING, AND PROLONGED BURN PERIODS.
LONG TERM
ISSUED AT 1243 AM PDT SAT OCT 3 2026
(MONDAY THROUGH FRIDAY)
THE HEAT ADVISORY WILL REMAIN IN EFFECT THROUGH 10 PM MONDAY FOR THE
INTERIOR BAY AREA AND CENTRAL COAST. UPPER-LEVEL SHORTWAVE TROUGHING
WILL UNDERCUT THE RIDGE AND BRING AN INCREASE IN ONSHORE FLOW
MONDAY; HOWEVER, THE INTERIOR WILL REMAIN HOT. GLOBAL ENSEMBLE
CLUSTERS ARE IN AGREEMENT THAT HEIGHTS WILL REBUILD TUESDAY AND PEAK
WEDNESDAY. WITH LITTLE CHANGE IN THE DAY-TO-DAY FORECAST AND THE
CUMULATIVE HEAT IMPACTS, WE COULD BE LOOKING AT AN EXTENDED HEAT
ADVISORY. THIS IS ESPECIALLY TRUE FOR THE EAST BAY AND SOUTH BAY
WHERE MAJOR HEATRISK IS LIKELY (60%+) THROUGH WEDNESDAY. THE MARINE
LAYER WILL REMAIN COMPRESSED DURING THIS TIME, KEEPING THE COAST
COOL AND LIKELY REDUCING VISIBILITY FROM FOG. ELEVATED FIRE WEATHER
CONDITIONS WILL CONTINUE IN THE HIGHER TERRAIN THROUGH THURSDAY FOR
HOT AND DRY CONDITIONS WITH PROMINENT THERMAL BELTING AND PROLONGED
BURN PERIODS. THURSDAY REMAINS UNCERTAIN ON RIDGE VS. TROUGH, BUT BY
FRIDAY IT IS LIKELY THAT HEIGHTS WILL BEGIN TO FALL.
AVIATION
(12Z TAFS)
ISSUED AT 512 AM PDT SAT OCT 3 2026
SATELLITE AND SURFACE OBSERVATIONS SHOW DENSE FOG WITH SURFACE
VISIBILITIES LESS THAN 1/4 MILE FROM THE SAN FRANCISCO PENINSULA
TO THE BIG SUR COASTLINE. STRONG RIDGING ALOFT HAS COMPRESSED THE
MARINE LAYER TO 500 TO 700 FEET. AWAY FROM THE IMMEDIATE COASTLINE
IT'S VFR. MARINE FOG IS EASIER TO SEE THIS MORNING WITH LESS HIGH
CLOUDINESS OBSCURING THE VIEW, WHICH IS ALSO ALLOWING FOR IMPROVED
NOCTURNAL RADIATIVE COOLING. IT MAY RADIATE ENOUGH HEAT OUT TO SPACE
THROUGH DAYBREAK TO ALLOW A FEW PATCHES OF VALLEY FOG /IFR-LIFR/ TO
TEMPORARILY FORM ACROSS THE INLAND VALLEYS. HOWEVER, THE PROXIMITY
OF THE WARMTH WITH THE LOWER LEVEL TEMPERATURE INVERSION IS LIKELY
AN OFFSET, BALANCING TO A HIGHER VALLEY FLOOR AIR TEMPERATURE MAKING
IT MORE DIFFICULT TO REACH THE DEW POINT TEMPERATURE (SATURATION).
HRRR OUTPUT SHOWS AT LEAST PATCHY LOW STRATUS AND FOG /IFR-LIFR/
ALONG THE COASTLINE IN THE VICINITY OF THE MONTEREY BAY AREA TONIGHT
AND SUNDAY MORNING, OTHERWISE VFR.
VICINITY OF SFO...LOW TO MODERATE CONFIDENCE VFR CONTINUES THROUGH
DAYBREAK WITHOUT RADIATIVE COOLING LEADING TO FOG DEVELOPMENT. VFR
IS OTHERWISE FORECAST FOR THE 12Z TAF. LIGHT WEST WIND BECOMING LIGHT
NORTHEAST THIS MORNING THEN NORTHWEST TO WEST 7 TO 13 KNOTS IN THE
AFTERNOON AND TONIGHT.
SFO BRIDGE APPROACH...SIMILAR TO SFO.
MONTEREY BAY TERMINALS...WITH THE LOSS OF HIGH CLOUDINESS,
RADIATIVE COOLING WILL DOMINATE THROUGH DAYBREAK COMBINING WITH
RESIDUAL COOLER AIR RELATIVE TO SEA SURFACE TEMPERATURES RESULTING
IN DENSE FOG THROUGH 16Z (9 AM PDT). THERE'S BEEN SOME DISRUPTION
IN THE FOG DUE TO COOL AIR DRAINAGE WINDS AND MIXING. DIURNAL MIXING
AND THE SHALLOW DEPTH OF THE MARINE LAYER I.E. A CLOSER PROXIMITY
TO THE LOWER LEVEL TEMPERATURE INVERSION WILL PRODUCE SUFFICIENT
MIXING TO ERODE THE FOG LATER IN THE MORNING. OTHERWISE VFR IS
FORECAST TODAY. EAST TO SOUTHEAST COOL AIR DRAINAGE WINDS AROUND
5 KNOTS KMRY AND UP TO 10 KNOTS AT KSNS DURING THE MORNING. WINDS
SHIFTING TO NORTHWEST 5 TO 10 KNOTS IN THE AFTERNOON.
LOW TO MODERATE CONFIDENCE LOW STRATUS AND FOG /LIFR/ RETURN
TONIGHT AND SUNDAY MORNING BASED ON RECENT HRRR OUTPUT. WINDS
BECOMING LIGHT AND VARIABLE IN THE EVENING, THEN LIGHT EAST TO
SOUTHEAST TONIGHT AND SUNDAY MORNING.
MARINE
(TODAY THROUGH THURSDAY)
ISSUED AT 426 AM PDT SAT OCT 3 2026
A SHALLOW MARINE LAYER HAS RESULTED IN AREAS OF DENSE FOG ALONG
THE COASTLINE TO THE MONTEREY BAY WITH VISIBILITY LESS THAN 1/4
MILE. DENSE FOG WILL MIX OUT LATER IN THE MORNING. NORTHWESTERLY
BREEZES REMAIN GENTLE TO MODERATE INTO EARLY WEEK, ALLOWING FOR
SLIGHT TO MODERATE SEAS TO PERSIST.
FIRE WEATHER
ISSUED AT 458 AM PDT SAT OCT 3 2026
HOT AND DRY CONDITIONS ARE FORECAST THROUGH NEXT WEEK, WHICH WILL
BE ACCOMPANIED WITH WEAK OFFSHORE FLOW. POOR TO VERY POOR
OVERNIGHT RECOVERY IS EXPECTED FOR THE THERMAL BELTS, GENERALLY
FOR ELEVATIONS ABOVE 1000-1500 FEET, LEADING TO ELEVATED FIRE
WEATHER CONDITIONS. THE MARINE LAYER IS EXPECTED TO BE CONFINED TO
THE IMMEDIATE COAST AND AROUND 500 FEET. A PATTERN CHANGE BEGINS
LATE THURSDAY INTO FRIDAY, WHICH MAY LEAD TO COOLER WEATHER AND
THE POTENTIAL FOR IMPROVED RH RECOVERY.
MTR WATCHES/WARNINGS/ADVISORIES
CA...HEAT ADVISORY FROM 11 AM THIS MORNING TO 10 PM PDT SUNDAY FOR
CAZ006-502-528-529.
HEAT ADVISORY FROM 11 AM THIS MORNING TO 10 PM PDT MONDAY FOR
CAZ503-504-506-508-510-512>518.
DENSE FOG ADVISORY UNTIL 9 AM PDT THIS MORNING FOR CAZ509-529-
530.
PZ...DENSE FOG ADVISORY UNTIL 9 AM PDT THIS MORNING FOR MRY BAY.
SHORT TERM...SARMENT
LONG TERM....SARMENT
AVIATION...CANEPA
MARINE...CANEPA
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