147
FXUS66 KMTR 241827
AFDMTR
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SAN FRANCISCO CA
1127 AM PDT MON AUG 24 2026
..NEW AVIATION, MARINE
KEY MESSAGES
UPDATED AT 1200 AM PDT MON AUG 24 2026
- TEMPERATURES NEAR TO SLIGHTLY BELOW SEASONAL AVERAGES PERSIST
WITHIN THE MARINE LAYER THROUGH THE REST OF THE WEEK
- WARM AND DRY CONDITIONS CONTINUE ABOVE 1000 FEET
- PATTERN CHANGE FRIDAY INTO THE WEEKEND BRINGS COOLER
TEMPERATURES AND POSSIBLE TROPICAL MOISTURE
SHORT TERM
ISSUED AT 1200 AM PDT MON AUG 24 2026
(TODAY AND TONIGHT)
FOR THE LAST COUPLE OF DAYS WE'VE WRITTEN THE TALE OF A BATTLE
BETWEEN THE EASTERN PACIFIC TROUGH AND THE DESERT SOUTHWEST RIDGE
THAT HAS DOMINATED OUR WEATHER PATTERN. TODAY IT'S THE TROUGHING
THAT WILL TAKE THE UPPER HAND AS A CUTOFF LOW INCHES TOWARDS THE
PACIFIC NORTHWEST, LEADING TO SLIGHTLY COOLER TEMPERATURES AND
CLOUDIER MORNINGS ACROSS THE REGION. ANOTHER INTERESTING FACTOR
TODAY IS A WEAK SHORTWAVE TROUGH COMING INTO THE REGION THROUGH THE
MORNING. THE TWO MAIN GLOBAL WEATHER MODELS, THE EUROPEAN ECMWF AND
THE AMERICAN GFS, ARE SHOWING THAT THERE COULD BE ENOUGH
INSTABILITY, MOISTURE, AND LIFT TO MAYBE, JUST MAYBE, SUPPORT A FEW
HIGH-BASED THUNDERSTORMS DEVELOPING ACROSS THE NORTH BAY,
PARTICULARLY OVER NAPA COUNTY. THIS IS A VERY LOW PROBABILITY
FORECAST (AROUND 5% CHANCE THROUGH AROUND 11 AM), ALONG WITH A LOW
CONFIDENCE FOR STORM DEVELOPMENT. THE HIGHER RESOLUTION NAM, HRRR,
AND RRFS MODELS DO NOT SHOW ANY SIGNS OF DEVELOPING STORMS, LAPSE
RATES ALOFT ARE MARGINAL AT BEST, AND K-INDEX VALUES BELOW 20
DEGREES CELSIUS SUGGEST NO CHANCE FOR DEVELOPING THUNDERSTORMS. ANY
PRECIPITATION THAT DOES DEVELOP IS ALSO LIKELY TO END UP AS VIRGA,
EVAPORATING WITHIN THE VAST DRY LOW LAYER WHERE RELATIVE HUMIDITY
VALUES AS OF THE 0Z (5 PM PDT) OAK SOUNDING FELL INTO THE SINGLE
DIGITS.
TODAY'S HIGHS RANGE FROM THE 80S INTO THE LOWER 90S FOR THE INLAND
VALLEYS, THE MIDDLE 90S TO THE TRIPLE DIGITS ACROSS THE WARMEST
INTERIOR SPOTS, THE UPPER 60S TO THE UPPER 70S NEAR THE BAYS, AND
THE UPPER 50S TO THE MIDDLE 60S ALONG THE PACIFIC COAST. THE HIGHER
ELEVATIONS ABOVE THE MARINE LAYER INFLUENCE WILL REMAIN RATHER DAY,
ESPECIALLY DURING THE AFTERNOON AND EVENING HOURS. BREEZY ONSHORE
PATTERN WINDS WILL DEVELOP THIS AFTERNOON AND EVENING WITH WIND
GUSTS REACHING 20 TO 30 MPH ALONG COASTAL JET REGIONS, THROUGH
FAVORED GAPS AND PASSES, AND WITHIN THE NORTHERN SALINAS VALLEY.
SMOKE FROM THE TIMBER FIRE WILL CONTINUE IMPACTING THE IMMEDIATE
AREA AROUND THE ACTIVELY BURNING FIRE THROUGH THE DAY, WITH WINDS
ALOFT LOFTING THE SMOKE PLUME OVER SALINAS AND HOLLISTER. FOR AIR
QUALITY INFORMATION, REFER TO PRODUCTS ISSUED BY THE MONTEREY BAY
AIR RESOURCES DISTRICT.
LONG TERM
ISSUED AT 1200 AM PDT MON AUG 24 2026
(TUESDAY THROUGH SUNDAY)
TEMPERATURES REBOUND TUESDAY AND WEDNESDAY AS THE RIDGE REASSERTS
ITSELF, WITH THE INLAND VALLEYS REACHING HIGHS IN THE MIDDLE 80S TO
THE MIDDLE 90S ON WEDNESDAY AND THURSDAY WHILE THE BAYS REACH THE
LOWER 70S TO THE LOWER 80S. A PATTERN CHANGE WILL BEGIN LATER ON
THURSDAY AS A DEEP TROUGH BUILDS INTO THE WEST COAST WHILE THE RIDGE
BEGINS TO INCH ITS WAY EASTWARDS TOWARDS THE SOUTHERN PLAINS. IT
WILL BE INTERESTING TO SEE WHAT THE TROUGH WILL DO AS THE UPCOMING
WEEKEND COMES CLOSER AND WE ARE BETTER ABLE TO REFINE THE FORECAST.
ALSO WORTH A MENTION IS THE POSSIBILITY OF TROPICAL MOISTURE COMING
INTO THE REGION, WITH OUR COLLEAGUES AT THE NATIONAL HURRICANE
CENTER TRACKING TROPICAL STORM ISELLE AND THREE OTHER AREAS OF
INTEREST OFF THE COAST OF MEXICO. WHILE THE CIRCULATIONS REMAIN FAR
TO THE SOUTH OF OUR WATERS, THE RESULTANT MOISTURE WILL BE CAPTURED
BY THE DEVELOPING TROUGH WITH A WIDE VARIATION IN JUST HOW FAR NORTH
THE MOISTURE GOES. BY WAY OF EXAMPLE, THE DETERMINISTIC EUROPEAN
ECMWF MODEL BRINGS A SWATH OF TROPICAL MOISTURE INTO THE SAN
FRANCISCO BAY AREA BY FRIDAY MORNING, WHEREAS THE DETERMINISTIC GFS
KEEPS THE MOISTURE PLUME TO THE SOUTH OF MONTEREY COUNTY. IN
ADDITION, WAVE MODELS ARE ALSO SHOWING AN INCREASE IN SOUTHERLY
SWELLS AS THE TROPICAL EASTERN PACIFIC REMAINS ACTIVE INTO THE EARLY
PART OF NEXT WEEK.
AVIATION
(18Z TAFS)
ISSUED AT 1126 AM PDT MON AUG 24 2026
A BLANKET OF STRATUS HAS RETREATED TO THE COASTLINE RESULTING IN VFR
CONDITIONS FOR MOST TERMINALS, EXCEPT FOR HAF. HAF MAY BRIEFLY
SCATTER OUT THIS AFTERNOON, BUT WILL MAINLY REMAIN IFR THROUGH THE
TAF PERIOD. MODERATE ONSHORE FLOW PERSISTS DURING THE DAY WHICH WILL
ALLOW FOR A MORE PROMINENT INLAND PUSH OF STRATUS TONIGHT. THE
MARINE LAYER IS EXPECTED TO BE AROUND 1000 TO 1200 FEET OVERNIGHT
WHICH WILL BE SUFFICIENT ENOUGH TO REACH MOST TERMINALS. HIGH
CONFIDENCE FOR COASTAL SITES (HAF, MRY, AND SNS) TO DEVELOP IFR TO
LIFR CEILINGS AS EARLY AS SUNSET. MEDIUM CONFIDENCE ON THE EXACT
ARRIVAL OF IFR TO MVFR CEILINGS ELSEWHERE, THOUGH THEY MAY ARRIVE AS
EARLY AS 04-06Z TUESDAY.
VICINITY OF SFO...VFR THROUGH THE AFTERNOON AS WESTERLY WINDS
INCREASE TO AROUND 15 KT. BORDERLINE MVFR-IFR CEILINGS ARE EXPECTED
TONIGHT WITH THE SHALLOW MARINE LAYER AND PERSISTENT ONSHORE PUSH,
IT JUST BECOMES A MATTER OF WHEN. HIGH CONFIDENCE OAK WILL DEVELOP
CEILINGS BEFORE SFO, THOUGH MEDIUM CONFIDENCE ON THE ARRIVAL AS THEY
MAY ROLL IN A FEW HOURS LATER THAN SPECIFIED.
SFO BRIDGE APPROACH...SIMILAR TO SFO.
MONTEREY BAY TERMINALS...IFR TO LIFR CEILINGS WILL CONTINUE TO LIFT
THIS MORNING WITH VFR CONDITIONS TO PREVAIL THIS AFTERNOON. AN EARLY
RETURN OF IFR CONDITIONS IS LIKELY WITH CEILINGS GRADUALLY LOWERING
TO LIFR BY LATE THIS EVENING/OVERNIGHT. SOME POTENTIAL FOR
REDUCTIONS IN VISIBILITY EARLY TOMORROW MORNING BUT THAT WILL DEPEND
HOW MUCH THE MARINE LAYER COMPRESSES AND IF FOG IS ABLE TO DEVELOP.
BREEZY ONSHORE WINDS CONTINUE THIS AFTERNOON/EVENING BEFORE WINDS
EASE OVERNIGHT.
MARINE
(TODAY THROUGH SATURDAY)
ISSUED AT 1126 AM PDT MON AUG 24 2026
NORTHWEST LIGHT TO MODERATE BREEZES CONTINUE INTO TUESDAY AND
GRADUALLY INCREASE TO FRESH BY THE MIDDLE OF THE WEEK. WIND DRIVEN
SEAS REMAIN SLIGHT TO MODERATE, THOUGH A LONG PERIOD SWELL IS
EXPECTED TO APPROACH OUR COASTAL WATERS BY THE END OF THE WEEK.
SMOKE FROM THE TIMBER FIRE CONTINUES TO IMPACT VISIBILITY TO AS
LOW AS 2 MILES ALONG THE BIG SUR COAST.
MTR WATCHES/WARNINGS/ADVISORIES
CA...NONE.
PZ...NONE.
SHORT TERM...DIALH
LONG TERM....DIALH
AVIATION...NAVARRETE
MARINE...NAVARRETE
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