717
FXUS66 KMTR 261130
AFDMTR
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SAN FRANCISCO CA
430 AM PDT WED AUG 26 2026
..NEW AVIATION, MARINE
KEY MESSAGES
UPDATED AT 1209 AM PDT WED AUG 26 2026
- TEMPERATURES NEAR TO SLIGHTLY BELOW SEASONAL AVERAGES PERSIST
WITHIN THE SHALLOW MARINE LAYER THROUGH THURSDAY
- SEASONABLY WARM AND VERY DRY CONDITIONS CONTINUE ABOVE 1000
FEET AND THE FAR INTERIOR THROUGH THURSDAY
- PATTERN CHANGE FRIDAY INTO THE WEEKEND BRINGS COOLER
TEMPERATURES AND MODERATE POTENTIAL FOR TROPICAL MOISTURE
SHORT TERM
ISSUED AT 1209 AM PDT WED AUG 26 2026
(TODAY AND TONIGHT)
STRATUS CLOUDS ARE DEVELOPING AT THE IMMEDIATE COAST AND WILL EXPAND
INTO THE COASTAL VALLEYS THROUGH THE NIGHT, BEFORE MIXING OUT
WEDNESDAY MORNING. THE WEATHER PATTERN TODAY REMAINS DOMINATED BY
THE BALANCE BETWEEN RIDGING IN THE DESERT SOUTHWEST AND TROUGHING IN
THE EASTERN PACIFIC, WITH A SLIGHT EDGE TO THE RIDGING AS REFLECTED
IN A GENERAL WARMING TREND ACROSS THE REGION. HIGHS IN THE INLAND
VALLEYS REACH THE MIDDLE 80S TO THE MIDDLE 90S, UP TO 106 WITHIN THE
WARMEST REGIONS OF SOUTHERN MONTEREY COUNTY, WITH THE BAYS REACHING
THE MIDDLE 70S TO THE MIDDLE 80S AND THE PACIFIC COAST REMAINING
RATHER COOL IN THE LOWER TO MIDDLE 60S. A GENTLE TO MODERATE ONSHORE
BREEZE DEVELOPS IN THE AFTERNOON AND EVENING HOURS WITH GUSTS OF 20
TO 30 MPH AT THE COAST, THROUGH GAPS AND PASSES, AND WITHIN THE
SALINAS VALLEY. THE MARINE LAYER WILL REMAIN AROUND 1000-1500 FT
TODAY, WITH WARM AND DRY CONDITIONS ABOVE THE MARINE LAYER
INVERSION. SEE THE FIRE WEATHER SECTION FOR THE IMPLICATIONS FOR
LOCAL FIRE WEATHER CONCERNS.
LONG TERM
ISSUED AT 1209 AM PDT WED AUG 26 2026
(THURSDAY THROUGH TUESDAY)
THE RIDGING REMAINS IN PLACE THROUGH THURSDAY WITH TEMPERATURE
AROUND THE SAME AS TODAY'S BEFORE THE TROUGH OVER THE EASTERN
PACIFIC BEGINS TO MIGRATE EASTWARDS LATE THURSDAY INTO FRIDAY,
STARTING A COOLING TREND THAT WILL LAST THROUGH THE EARLY PART OF
NEXT WEEK. AS THE TROUGH MOVES INTO THE WEST COAST, IT WILL PULL IN
TROPICAL MOISTURE PARTIALLY FROM WHAT WOULD BE THE REMNANTS OF
TROPICAL STORM ISELLE AND DIRECT IT TOWARDS THE STATE. THE MODEL
TREND FOR STEADILY INCREASING PRECIPITABLE WATER VALUES HAS
CONTINUED TO PLAY OUT, WITH ENSEMBLE MODEL PROBABILITIES SUGGESTING
THAT OAKLAND IS LIKELY TO SEE PRECIPITABLE WATER VALUES EXCEEDING
1.0 INCHES ON FRIDAY MORNING. FOR CONTEXT, THE 90TH PERCENTILE VALUE
FOR PRECIPITABLE WATER AT OAK IS 1.04 INCHES, AND PRETTY MUCH ALL
THE DETERMINISTIC MODELS THAT GO OUT THIS FAR HAVE OAK EXCEEDING
THIS VALUE, WITH SOME OF THE WETTER MODELS MAKING A RUN FOR OR
EXCEEDING THE DAILY MAXIMUM VALUE, WHICH FOR THE 12Z (5 AM PDT)
SOUNDINGS ON AUGUST 28, WOULD BE 1.24 INCHES. THIS KIND OF SETUP
WOULD DEFINITELY BRING HIGH CLOUDS TO THE REGION AND ALSO BRINGS THE
RISK OF HIGH-BASED RAIN SHOWERS AND THUNDERSTORMS TO THE REGION. ONE
OF THE BIG CAVEATS OF THIS RISK, ESPECIALLY AS IT PERTAINS TO
THUNDERSTORMS, IS THAT MODEL OUTPUT ALSO SUGGESTS THAT INSTABILITY
IS LACKING WITH THE EUROPEAN MODEL SHOWING VIRTUALLY NO CAPE
ANYWHERE WITHIN THE ATMOSPHERE, SURFACE OR ELEVATED. WE WILL
CONTINUE TO MONITOR THE EVOLUTION OF THIS SETUP CLOSELY.
THE INCOMING TROUGH WILL ALSO LEAD TO AN TIGHTENING OF THE PRESSURE
GRADIENT, WHICH IN TURN WILL LEAD TO BREEZIER WINDS FRIDAY INTO THE
WEEKEND. GUSTS WILL RISE TO 25 TO 35 MPH ALONG THE COAST AND THROUGH
FAVORED GAPS, VALLEYS, AND PASSES. THE TROUGHING PATTERN WILL
CONTINUE TO DEVELOP INTO THE EARLY PART OF NEXT WEEK, WHEN
TEMPERATURES WILL DIP 5 TO 15 DEGREES BELOW THE SEASONAL AVERAGE,
WITH HIGHS IN THE 70S TO LOWER 80S IN THE INTERIOR VALLEYS. THE
CURRENT FORECAST HAS SOME RAIN CHANCES RETURNING TOWARDS THE
MIDDLE OF NEXT WEEK, BUT THIS IS CRITICALLY DEPENDENT ON THE
FUTURE EVOLUTION OF THE SITUATION IN THE TROPICAL EAST PACIFIC,
AND AS A RESULT THE CONFIDENCE IN THIS FORECAST IS VERY LOW AT
THIS TIME.
AVIATION
(12Z TAFS)
ISSUED AT 419 AM PDT WED AUG 26 2026
THE MID/HIGH CLOUDS MOVED OUT OF OUR AREA AND THE MARINE LAYER
QUICKLY REORGANIZED AND MADE A PUSH INLAND. IFR/LIFR HAS DEVELOPED
FOR A MAJORITY OF THE TERMINALS WITH KLVK LIKELY TO BE THE ONLY
SITE IMPACTED BY STRATUS CEILINGS THROUGH THE REMAINDER OF THE
FORECAST PERIOD.
VICINITY OF SFO...A STEADY FETCH OF ONSHORE FLOW CHANNELING
THROUGH THE BAY AREA WAS INTERRUPTED BRIEFLY BY HIGH CLOUDS
EARLIER TUESDAY NIGHT INTO THIS MORNING BUT HAS NOW BEGUN TO
INCREASE IN COVERAGE. VFR CEILINGS ARE EXPECTED BY MID-MORNING AS
STRATUS RETREATS BACK TOWARD THE COASTLINE.
SFO BRIDGE APPROACH...SIMILAR TO SFO.
MONTEREY BAY TERMINALS...IFR/LIFR CEILINGS DEVELOPED IN THE WAKE
OF UPPER LEVEL CLOUDS, AFTER IS SEEMED POSSIBLE STRATUS MIGHT NOT
FILL IN. COVERAGE IS STILL NOT AS EXTENSIVE AS NORMALLY SEEN AT
THIS TIME, WITH VFR EXPECTED BY MID TO LATE MORNING. IFR/LIFR
CEILINGS AREN'T EXPECTED TO RETURN UNTIL AROUND SUNSET.
MARINE
(TODAY THROUGH MONDAY)
ISSUED AT 419 AM PDT WED AUG 26 2026
FRESH TO STRONG NORTHWEST WINDS WILL CONTINUE TODAY INTO THE
WEEKEND WITH MODERATE WIND DRIVEN SEAS. A LONG PERIOD SOUTHERLY
SWELL WILL BUILD LATE IN THE WEEK BECOMING 17-18 SECONDS BY FRIDAY
AND PERSIST THROUGH AT LEAST EARLY SUNDAY.
FIRE WEATHER
ISSUED AT 1209 AM PDT WED AUG 26 2026
NOT MUCH HAS CHANGED IN TERMS OF THE FIRE WEATHER THREAT, WITH NEAR
CRITICAL FIRE WEATHER CONDITIONS PERSISTING IN THE HIGHER ELEVATIONS
ABOVE 1000 FEET THROUGH THURSDAY DUE TO WARM AND DRY CONDITIONS.
OVERNIGHT HUMIDITY RECOVERIES REMAIN POOR TO VERY POOR WITHIN THESE
AREAS AND THE IMPACT OF THE MARINE LAYER INVERSION LEADS TO
TEMPERATURES WARMER THAN THE SEASONAL AVERAGE, ESPECIALLY WITHIN THE
SANTA LUCIA RANGE AND THE INTERIOR CENTRAL COAST WHERE TEMPERATURE
ARE RUNNING AS MUCH AS 15 TO 20 DEGREES ABOVE THE SEASONAL
AVERAGE. MODEL OUTPUT SUGGESTS THAT AN OFFSHORE FLOW HAS SET UP
OVER THE BIG SUR COAST AT THE 925 MB LEVEL, SUPPORTING THE RISK
FOR OVERNIGHT NOCTURNAL DRYING IN THE INTERIOR CENTRAL COAST AND
PARTICULARLY SURROUNDING THE TIMBER FIRE. LAST NIGHT I HAD NOTED
THAT THE SOUTHWEST WINDS SEEMED TO BRING IN MORE MOIST AIR INTO
THE SANTA LUCIA RANGE, AND THAT THE OVERNIGHT DIMINISHING OF WINDS
WHEN COMBINED WITH THE OFFSHORE PUSH LED TO AN UNUSUAL SITUATION
WHERE THE MAXIMUM DAILY RELATIVE HUMIDITIES TOOK PLACE DURING THE
DAY. THIS REMAINS THE CASE, UP UNTIL THE RIDGELINE PARALLEL TO THE
BIG SUR COAST WHEN THE SOUTHWEST WINDS BEGIN TO DOWNSLOPE AND DRY
THE REGION. UNFORTUNATELY THERE AREN'T A LOT OF WEATHER STATION
IN THESE AREAS TO VERIFY THE CONCEPTUAL MODEL. SMOKE TRANSPORT
FROM THE TIMBER FIRE WILL CONTINUE TO PEAK IN THE AFTERNOON AND
EVENING WITH THE PLUME SPREADING TOWARDS THE SALINAS AREA. FRIDAY
INTO THE WEEKEND, A PATTERN CHANGE SHOULD ALLOW FOR SOME RELIEF AS
AN UPPER LEVEL TROUGH COMES INTO THE REGION BRINGING COOLER
TEMPERATURES AND A DEEPER MARINE LAYER.
DIALH
MTR WATCHES/WARNINGS/ADVISORIES
CA...NONE.
PZ...SMALL CRAFT ADVISORY UNTIL 9 AM PDT FRIDAY FOR PIGEON PT TO PT
PINOS 0-10 NM-PIGEON PT TO PT PINOS 10-60 NM-PT ARENA TO PT
REYES 0-10 NM-PT ARENA TO PT REYES 10-60 NM-PT PINOS TO PT
PIEDRAS BLANCAS 0-10 NM.
SHORT TERM...DIALH
LONG TERM....DIALH
AVIATION...JM
MARINE...JM
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