436
FXUS66 KMTR 192337
AFDMTR
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SAN FRANCISCO CA
437 PM PDT SAT SEP 19 2026
..NEW AVIATION, MARINE
KEY MESSAGES
UPDATED AT 1229 PM PDT SAT SEP 19 2026
- WARMER TEMPERATURES TODAY
- BRIEF COOLING SUNDAY THROUGH MONDAY
- MORE SUBSTANTIAL WARMING TREND TUESDAY THROUGH THURSDAY
SHORT TERM
ISSUED AT 1229 PM PDT SAT SEP 19 2026
(THIS EVENING THROUGH SUNDAY NIGHT)
THE MARINE LAYER IS AROUND 1,500 FEET DEEP AND THE MORNING CLOUDS
HAVE PULLED BACK TO THE COAST. THERE IS A WEAK OFFSHORE GRADIENT
(SFO-WMC -3MB) THAT CAUSED SOME MODERATE NE WINDS ACROSS THE NORTH
BAY AND EAST BAY MOUNTAINS EARLY THIS MORNING. THE SEA BREEZE IS
NOW TAKING OVER, FLIPPING WINDS BACK ONSHORE AS THE MESOSCALE
GRADIENT WEAKENS. A 500 MB SHORT WAVE RIDGE AXIS WILL MOVE OVER
THE BAY AREA THIS AFTERNOON. THIS BUILDING RIDGE IS CAUSING
SUBSIDENCE AND WARMER CONDITIONS IN THE LOWER ATMOSPHERE. SURFACE
TEMPERATURES ARE AROUND 5 DEGREES WARMER THAN THIS TIME YESTERDAY
OUTSIDE OF THE CLOUDY COAST. THAT PUTS US RIGHT AROUND NORMAL FOR
THIS TIME OF YEAR.
A WEAK CUT-OFF LOW WILL START TO MOVE IN FROM THE WEST SUNDAY. THIS
WILL REVERSE THE WARMING TREND AND BRING TEMPERATURES AROUND 5-10
DEGREES BELOW NORMAL AGAIN. IT WILL ALSO ENCOURAGE THE THE MARINE
LAYER TO EXPAND A BIT.
LONG TERM
ISSUED AT 1229 PM PDT SAT SEP 19 2026
(MONDAY THROUGH NEXT FRIDAY)
THE CUT-OFF LOW WILL MOVE OVERHEAD MONDAY. THIS WILL KEEP THE COOLER
TEMPERATURES IN PLACE, DEEPEN THE MARINE LAYER, AND MAY BRING
SOME MORNING DRIZZLE TO THE COAST AND WINDWARD SLOPES. THE ECMWF
SHOWS SOME DECENT 850 MB VORTICITY, WHICH WILL HELP CREATE THE
LIFT NECESSARY TO FORM DRIZZLE DROPS WITHIN THE DEEPER CLOUD
LAYER. THESE ARE STILL TINY DRIZZLE DROPS THOUGH, SO ANY
ACCUMULATION WILL BE VERY LIGHT.
BY TUESDAY WE WILL BE ON THE BACKSIDE OF THE LOW AND A MORE
SUBSTANTIAL WARMING TREND WILL BEGIN. A RELATIVELY LOW-AMPLITUDE
500 MB RIDGE WILL BUILD THROUGH THE MIDDLE OF THE WEEK, BUT 850
TEMPERATURES WILL CLIMB TO 20 TO 23C BY WEDNESDAY AND THURSDAY.
THAT RANGE IS APPROXIMATELY THE 75TH TO 95TH PERCENTILE FOR THIS
TIME OF YEAR. OUR CURRENT FORECAST HAS NEAR NORMAL TEMPERATURES
ACROSS THE INTERIOR TUESDAY, STEADILY BUILDING TO 10 TO 15 DEGREES
ABOVE NORMAL BY THURSDAY. WITH NO SIGN OF STRONG OFFSHORE WINDS,
A SHALLOW MARINE LAYER WILL LIKELY SURVIVE THIS WARM-UP, AT LEAST
THROUGH WEDNESDAY. HEAT ADVISORIES ARE POSSIBLE, BUT WE'RE GETTING
TO THE TIME OF YEAR WHERE THE NIGHTS ARE JUST AS LONG AS THE
DAYS, WHICH REALLY HELPS DULL THE ACCUMULATING IMPACTS.
THE RIDGE WILL START TO BREAK DOWN FRIDAY AS A 500 MB TROUGH
MOVES OVER THE PACIFIC NORTHWEST. THIS WILL BRING TEMPERATURES
BACK DOWN. THERE'S STILL NO REAL CHANCE FOR RAIN UNTIL THE
FOLLOWING WEEK.
AVIATION
(00Z TAFS)
ISSUED AT 437 PM PDT SAT SEP 19 2026
VFR PREVAILS EXCEPT FOR COASTAL STRATUS AND MIST/FOG /IFR/. SFO-SAC
PRESSURE GRADIENT IS 2.4 MB WITH ONSHORE WINDS BRINGING STRATUS AND
MIST/FOG /IFR-LIFR/ INLAND TONIGHT AND SUNDAY MORNING. CONDITIONS
IMPROVE TO MVFR-VFR NEAR THE COASTLINE SUNDAY AFTERNOON WHILE VFR
CONTINUES FARTHEST INLAND.
VICINITY OF SFO...VFR AND A WEST WIND 20 TO 25 KNOTS DURING THE
EVENING, WEST WIND THEN DIMINISHING TO NEAR 10 KNOTS TONIGHT AND
SUNDAY MORNING. MVFR STRATUS CEILING FORECAST 06Z-19Z SUNDAY. WEST
WIND 10 TO 15 KNOTS SUNDAY AFTERNOON AND EVENING.
SFO BRIDGE APPROACH...SIMILAR TO SFO.
MONTEREY BAY TERMINALS...STRATUS AND MIST/FOG /IFR-LIFR/ ARE NEARBY
AND WILL MOVE INLAND TONIGHT AND SUNDAY MORNING. CONDITIONS IMPROVE
TO MVFR-VFR BY LATE SUNDAY MORNING AND AFTERNOON. MAINLY ONSHORE
WINDS 5 TO 15 KNOTS.
MARINE
(TONIGHT THROUGH NEXT THURSDAY)
ISSUED AT 428 PM PDT SAT SEP 19 2026
MODERATE NORTHWEST WINDS WILL CONTINUE TONIGHT INTO SUNDAY THEN
INCREASE SUNDAY AFTERNOON AND EVENING AS A WEAK UPPER LOW
APPROACHES THE REGION. FRESH WIND WAVE SEAS WILL CONTINUE OVER A
LONG PERIOD SOUTHERLY SWELL. HIGH PRESSURE BUILDS TUESDAY THROUGH
THURSDAY WITH WINDS EASING NEAR SHORE.
FIRE WEATHER
ISSUED AT 1229 PM PDT SAT SEP 19 2026
THE MARINE LAYER IS AROUND 1,500 FEET DEEP AND COMPRESSING. THERE
WERE SOME OFFSHORE WINDS THIS MORNING, BUT THE SEA BREEZE IS
TAKING OVER AS THE OFFSHORE GRADIENT RELAXES. TODAY WILL BE WARMER
AND SLIGHTLY DRIER THAN RECENT DAYS, ALTHOUGH WINDS WILL BE
LIGHTER THROUGH THE PEAK BURN PERIOD. COOLER AND MORE HUMID
CONDITIONS ARRIVE SUNDAY-MONDAY BEFORE A LONGER WARMING TREND
TUESDAY THROUGH THURSDAY.
MTR WATCHES/WARNINGS/ADVISORIES
CA...NONE.
PZ...SMALL CRAFT ADVISORY UNTIL 9 AM PDT SUNDAY FOR PT ARENA TO PT
REYES 0-10 NM.
SMALL CRAFT ADVISORY UNTIL 3 AM PDT SUNDAY FOR PIGEON PT TO PT
PINOS 0-10 NM.
SMALL CRAFT ADVISORY FROM 3 PM TO 9 PM PDT SUNDAY FOR PIGEON PT
TO PT PINOS 0-10 NM.
SMALL CRAFT ADVISORY UNTIL 3 AM PDT MONDAY FOR PIGEON PT TO PT
PINOS 10-60 NM-PT PINOS TO PT PIEDRAS BLANCAS 0-10 NM.
SMALL CRAFT ADVISORY UNTIL 9 AM PDT MONDAY FOR PT ARENA TO PT
REYES 10-60 NM.
SHORT TERM...FLYNN
LONG TERM....FLYNN
AVIATION...CANEPA
MARINE...RW
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