265
FXUS66 KMTR 050006
AFDMTR
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SAN FRANCISCO CA
506 PM PDT TUE AUG 4 2026
..NEW AVIATION, MARINE
KEY MESSAGES
UPDATED AT 109 PM PDT TUE AUG 4 2026
- MODERATE HEATRISK IN THE INTERIOR TODAY DECREASING MIDWEEK.
- ELEVATED FIRE WEATHER THREAT ACROSS THE INTERIOR NORTH AND EAST
BAYS, AND THE DIABLO AND SANTA LUCIA RANGES THROUGH THE WEEK.
- WIDESPREAD MODERATE HEATRISK RETURNS FOR THE END OF THE WORK
WEEK.
- CRITICAL FIRE WEATHER CONDITIONS DEVELOP FRIDAY AND SATURDAY.
SHORT TERM
ISSUED AT 109 PM PDT TUE AUG 4 2026
(THIS EVENING THROUGH WEDNESDAY NIGHT)
REST OF TODAY: MARINE LAYER ROLLED BACK TO THE COAST, BUT IS
HANGING PRETTY SOLID ALONG THE COASTLINE. LINGERING MARINE LAYER
PLUS A SLIGHTLY STRONGER ONSHORE FLOW EQUALS AN IMPRESSIVE 24 HOUR
TREND. TEMPERATURES AS OF 1 PM ARE CURRENTLY RUNNING A FEW
DEGREES COOLER TO AS MUCH A 20 DEGREES THAN MONDAY. WARMEST
LOCATIONS IN THE FORECAST AREA ARE ACROSS THE INTERIOR WITH
TEMPERATURES STILL IN THE MID 90S TO LOW 100S EVEN WITH THE
COOLING TREND. WILL KEEP HEAT ADVISORY AS IS FOR NOW THROUGH 10
PM, BUT IT DOES APPEAR SOME SPOTS MAY FALL SHORT OF THEIR FORECAST
HIGHS.
ADDITIONALLY, VISIBLE SATELLITE IMAGERY ALSO SHOWS SMOKE LURKING
OVER THE COASTAL WATERS. THIS SMOKE IS ACTUALLY FROM THE PACNW
FIRES. LATEST SMOKE MODEL BRINGS SOME HIGH LEVEL SMOKE OVER THE
BAY AREA LATER TODAY, WHICH MAY CONTRIBUTE TO SOME HAZE OR JUST A
PRETTY SUNSET.
TONIGHT THROUGH WEDNESDAY NIGHT:
MARINE LAYER ALONG THE COAST WILL MARCH INLAND AGAIN TONIGHT. HAVE
ADDED ANOTHER ROUND OF COASTAL DRIZZLE. DEPTH OF THE MARINE LAYER
WILL REMAIN AROUND THE 1K FT MARK. ABOVE THE MARINE LAYER WILL
REMAIN MILD AND DRY WITH ACTIVE THERMAL BELTS.
THE COOLDOWN EXPERIENCE TODAY WILL CONTINUE ON WEDNESDAY THANKS
TO PERSISTENT ONSHORE FLOW, MARINE LAYER INFLUENCE, A WEAK
DISTURBANCE OVERHEAD RIDING THE PERIPHERY OF THE UPPER RIDGE.
EVENT WITH A "COOLDOWN" FAR INTERIOR LOCATIONS WILL BE WELL INTO
THE 90S WITH A FEW MAKING A RUN AT 100 DEGREES. HIGH PROBABILITY
OF EXCEEDING 100 DEGREE WILL BE INTERIOR MONTEREY/SAN BENITO
COUNTIES AND FAR INTERIOR EAST BAY. GIVEN THE SLIGHTLY COOLER
TEMPERATURES HEATRISK VALUES DECREASE. AS SUCH, WILL NOT BE
ISSUING A HEAT ADVISORY AT THIS TIME FOR WEDNESDAY.
WEDNESDAY NIGHT WILL FEATURE ANOTHER SOLID PUSH FROM THE MARINE
LAYER, BUT MAYBE A TAD MORE COMPRESSED GIVEN BUILDING H5.
LONG TERM
ISSUED AT 148 PM PDT TUE AUG 4 2026
(THURSDAY THROUGH NEXT MONDAY)
THURSDAY WILL BE A TRANSITION DAY AS MARINE LAYER COMPRESSES AND
THE UPPER LEVEL RIDGE MAKES ITS PRESENCE KNOWN AGAIN. TEMPERATURES
WILL BE MODERATING WITH A LARGE DIFFERENCE WITH COOL TEMPS AT
COAST AND MUCH HOTTER TEMPERATURES INLAND. BASICALLY, IN THE BIG
PICTURE NOTHING MAJOR FROM WHAT WE'VE BEEN SEEING. JUST THAT TEMPS
WILL BE COOL ENOUGH TO KEEP HEATRISK VALUES IN THE MINOR TO
MODERATE CATEGORIES.
FRIDAY THROUGH SATURDAY...THE UPPER LEVEL RIDGE BEGINS TO RE-ASSERT
ITS DOMINANCE WITH BUILDING 500MB HEIGHTS AND WARMING 850MB TEMPS
BACK TO CRITICAL LEVELS. THE BUILDING H5 WILL FURTHER COMPRESS THE
MARINE LAYER. THE MARINE LAYER WILL REMAIN HOWEVER. REALLY NEED
OFFSHORE FLOW TO GET RID OF THE MARINE LAYER AT THIS POINT. 850MB
TEMPS SOAR BACK INTO THE 28-30C RANGE, YIELDING INLAND MAX TEMPS
IN THE LOW 100S AND OVERNIGHT LOWS IN THE 70S. THAT COMBO WILL
INCREASE HEATRISK BACK INTO THE UPPER END OF MODERATE TO LOWER
MAJOR. THEREFORE, WE'LL LIKELY NEED A MIX OF HEAT ADV FOR INTERIOR
LOCATIONS FRIDAY/SATURDAY. STILL LOOKING ABOVE NORMAL AT THE
COAST/BAYS, BUT NATURAL AC WILL KEEP THE REAL HEAT INLAND.
INTERESTING LONGWAVE PATTERN IN THE EXTENDED AS THE UPPER LEVEL
RIDGE LOOKS TO BECOME MORE "SPLIT" WITH A SYSTEM SWEEPING THROUGH
PACNW. THE EASING UPPER LEVEL RIDGE WILL ALLOW FOR SUBTLE COOLING
ACROSS THE INTERIOR FOR SUNDAY AND MONDAY. WE'LL NEED TO TAKE A
CLOSER LOOK IF ANY HEAT ADV WILL BE NEEDED ON SUNDAY SINCE HEAT
IMPACTS ARE CUMULATIVE.
AVIATION
(00Z TAFS)
ISSUED AT 446 PM PDT TUE AUG 4 2026
A MORE ROBUST MARINE LAYER THAN THE PREVIOUS FEW DAYS/NIGHTS
REMAINS MOSTLY CONSTRAINED TO THE COASTLINE THIS AFTERNOON BUT
WILL BEGIN TO MAKE ITS WAY INLAND AROUND SUNSET TONIGHT, WITH ALL
TERMINALS EXPECTED TO SEE AT LEAST A SHORT PERIOD OF IFR/LIFR
CEILINGS THROUGH WEDNESDAY MORNING INTO THE EARLY AFTERNOON FOR
SOME.
VICINITY OF SFO...IFR/LIFR CEILINGS ARE EXPECTED TO SPREAD OVER
THE BAY AREA LATER THIS EVENING INTO THE OVERNIGHT HOURS WITH A
MORE ORGANIZED MARINE LAYER AND BREEZY ONSHORE FLOW HELPING
STRATUS TO SPILL OVER INTO THE BAY AREA BY MIDNIGHT. VFR
CONDITIONS ARE EXPECTED BY EARLY AFTERNOON, WITH A LOCAL OFFSHORE
CIRCULATION (OTTER EDDY) RESULTING IN MORE VARIABLE WIND
DIRECTIONS AT TIMES THROUGH MOST OF THE FORECAST PERIOD.
SFO BRIDGE APPROACH...SIMILAR TO SFO.
MONTEREY BAY TERMINALS...VFR CURRENTLY, HOWEVER STRATUS IS ALREADY
SPILLING INTO THE SALINAS VALLEY AND THE MONTEREY PENINSULA IN
VICINITY OF BOTH TERMINALS. ONCE CEILINGS SETTLE IN, IFR/LIFR IS
EXPECTED TO PERSIST THROUGH AT LEAST LATE MORNING, AND POSSIBLY INTO
EARLY AFTERNOON.
MARINE
(TONIGHT THROUGH NEXT SUNDAY)
ISSUED AT 446 PM PDT TUE AUG 4 2026
LIGHT TO GENTLE BREEZES WILL PERSIST ACROSS THE MAJORITY OF THE
COASTAL WATERS THROUGH LATE WEEK. A LOCALIZED GENTLE TO MODERATE
BREEZE CONTINUES ACROSS THE INNER WATERS. SEAS CONTINUE TO ABATE
THROUGH THURSDAY WITH WAVE HEIGHTS BETWEEN 4-8 FEET EXPECTED
THROUGH FRIDAY. THE PACIFIC HIGH STRENGTHENS AND SHIFTS EASTWARD
LATE THIS WEEK INTO THE WEEKEND, RESULTING IN STRENGTHENING WINDS
AND BUILDING SEAS WITH A RETURN OF HAZARDOUS CONDITIONS FOR SMALL
CRAFT.
FIRE WEATHER
ISSUED AT 155 PM PDT TUE AUG 4 2026
AFTER COORDINATING WITH NEIGHBORING OFFICES AND FIRE PARTNERS
FIRE WEATHER CONCERNS OVER THE NEXT 5 TO 7 DAYS REMAIN WITH
ELEVATED TO NEAR CRITICAL CONDITIONS.
TEMPERATURES REMAIN AROUND 10-15 DEGREES ABOVE NORMAL ACROSS THE
INTERIOR WITH THE EXCEPTION OF WEDNESDAY AND THURSDAY WHERE
TEMPERATURES ARE MORE SEASONAL. HIGH TEMPERATURES LARGELY REMAIN
IN THE UPPER 80S TO 90S WITH THE WARMEST LOCATIONS REACHING THE
LOW 100S. DAYTIME HUMIDITY RETENTION REMAINS POOR ACROSS THE
INTERIOR (15-30%) WITH HUMIDITY VALUES DROPPING INTO THE 10S
ACROSS THE INTERIOR CENTRAL COAST, EAST BAY HILLS/VALLEYS, AND THE
HIGHER ELEVATIONS. PORTIONS OF THE INTERIOR CENTRAL COAST MAY SEE
DAYTIME HUMIDITY VALUES DROP INTO THE SINGLE DIGITS TUESDAY, THEN
AGAIN TOWARDS THE END OF THE WEEK INTO THE WEEKEND. OVERNIGHT RH
RECOVERY REMAINS POOR AT LOCATIONS ABOVE 2,000 FEET WITH VALUES
BETWEEN 25 TO 40% EXPECTED WITH SOME FAVORED LOCATIONS STRUGGLING
TO REACH EVEN 25%. THIS WILL BE PARTICULARLY TRUE ACROSS THE
MAYACAMAS, HIGHEST PEAKS OF THE EAST BAY HILLS, THE DIABLO RANGE,
THE SANTA CRUZ MOUNTAINS, THE SANTA LUCIA AND GABILAN RANGES.
NOCTURNAL DRYING (RAPID DECREASE IN RH THROUGH THE PRE- DAWN
HOURS) MAY ALSO TRANSPIRE WHICH WILL INCREASE THE BURN PERIOD OR
TIME IN WHICH FIRE BEHAVIOR MAY REMAIN ACTIVE. ENERGY RELEASE
COMPONENT (ERC) VALUES HAVE CLIMBED ABOVE THE 97TH PERCENTILE
WITHIN THE INTERIOR CENTRAL COAST AND DIABLO-SANTA CRUZ (DIABLO
MOUNTAINS AND SANTA CRUZ MOUNTAINS) ZONES WITH THE MID COAST TO
MENDOCINO ZONE (NORTH BAY) TO REACH THE 97TH PERCENTILE THIS WEEK.
LARGE FIRES BECOME MORE FREQUENT AFTER ERC VALUES CROSS THE 90TH
PERCENTILE WITH EXTREME BURNING CONDITIONS EXPECTED WITH ERC
VALUES ABOVE THE 97TH PERCENTILE. 100 HR FUELS ARE ALSO RESPONDING
TO THE HOT AND DRY CONDITIONS WITH VALUES REACHING CRITICAL
LEVELS ACROSS THE REGION. LATEST INTEL ALSO SHOWS LIVE FUEL
SAMPLINGS ARE ALSO HEADING TOWARD CRITICAL LEVELS. THE ONE SAVING
GRACE IS THAT WE'RE NOT PREDICTING ANY LARGE WIND EVENTS OR
OFFSHORE FLOW WIND EVENTS DURING THIS TIME PERIOD. THAT BEING
SAID, DIURNALLY BREEZY ONSHORE WINDS ARE EXPECTED ALONG THE COAST,
MOUNTAIN GAPS AND PASSES, AND ALONG THE RIDGELINES EACH
AFTERNOON/EVENING. GIVEN THE ELEVATED FIRE WEATHER CONCERNS AND
VERY DRY FUELS, INDIVIDUAL ACROSS THE HIGHEST RISK AREAS (INTERIOR
NORTH AND EAST BAYS, THE DIABLO RANGE, THE SANTA LUCIA RANGE, AND
INTERIOR CENTRAL COAST) ARE ADVISED TO AVOID ACTIVITIES THAT MAY
SPARK A FIRE. THIS INCLUDES CAMPFIRES/BARBECUES AND MAKING SURE
CHAINS ARE SECURED TO AVOID SPARKS IF TOWING ANYTHING. FIRE CREWS
ARE URGED TO EXERCISE EXTRA CAUTION WHEN EXECUTING ANY PRESCRIBED
BURNS, ESPECIALLY WHERE FUELS, TOPOGRAPHY, AND WEATHER ALIGN.
MM/KR
MTR WATCHES/WARNINGS/ADVISORIES
CA...HEAT ADVISORY UNTIL 10 PM PDT THIS EVENING FOR CAZ510-513>515.
PZ...NONE.
SHORT TERM...MM
LONG TERM....MM
AVIATION...JM
MARINE...DIALH
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