688
FXUS66 KMTR 151052
AFDMTR
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SAN FRANCISCO CA
352 AM PDT MON SEP 15 2025
..NEW SHORT TERM, LONG TERM, AVIATION, MARINE
KEY MESSAGES
UPDATED AT 344 AM PDT MON SEP 15 2025
- ABOVE NORMAL TEMPERATURES TODAY THROUGH WEDNESDAY
- WIDESPREAD MODERATE HEATRISK TODAY THROUGH WEDNESDAY
- PATTERN SHIFT BRINGS CHANCES FOR ELEVATED DRY THUNDERSTORMS
THURSDAY AND FRIDAY
SHORT TERM
ISSUED AT 344 AM PDT MON SEP 15 2025
(TODAY AND TONIGHT)
A BUILDING RIDGE HAS BEGUN TO SHIFT ONSHORE OVERNIGHT. STRATUS WILL
CONTINUE TO HUG THE COASTLINE AS THE MARINE LAYER COMPRESSES AND
WEAK OFFSHORE FLOW DEVELOPS BY SUNRISE, WITH LOW STRATUS MIXING OUT
ENTIRELY BY MID/LATE MORNING. ONCE THE CLOUDS CLEAR, TEMPERATURES
WILL BEGIN TO RISE ABOVE NORMAL. INLAND TEMPERATURES, ESPECIALLY
HIGHER ELEVATIONS WILL SEE HIGHS RANGING FROM THE MID-80S TO UPPER
90S, WITH TEMPERATURES ALONG THE IMMEDIATE COAST IN THE 70S TO LOW
80S. ALTHOUGH A HEAT ADVISORY IS NOT NECESSARY TODAY, AREAS OF
MODERATE HEATRISK WILL MAKE BEING OUTSIDE FOR AN EXTENDED PERIOD OF
TIME UNCOMFORTABLE FOR WORKING OR RECREATION. REMEMBER TO REMAIN
HYDRATED WITH PLENTY OF WATER AND ELECTROLYTES, LIMIT TIME OUTDOORS
DURING PEAK HEATING IF POSSIBLE, AND NEVER LEAVE CHILDREN OR PETS
UNATTENDED IN VEHICLES.
WITH LITTLE TO NO MARINE LAYER INFLUENCE TONIGHT INTO EARLY TUESDAY
MORNING, WE'LL SEE POOR RH RECOVERY AWAY FROM THE DIRECT
COASTLINE, ESPECIALLY AT HIGHER ELEVATIONS. THE WARMER OVERNIGHT
LOWS AND DRIER AIRMASS WILL LEAD TO ACCELERATED DRYING OF FINER
FUELS (GRASSES/BRUSH) OVER THE NEXT FEW DAYS, WHICH WILL INCREASE
FIRE WEATHER CONCERNS LATER THIS WEEK, WITH MORE DETAILS IN THE
FIRE WEATHER SECTION BELOW.
LONG TERM
ISSUED AT 344 AM PDT MON SEP 15 2025
(TUESDAY THROUGH SUNDAY)
THE WARMEST TEMPERATURES AND LARGEST AREAL COVERAGE OF MODERATE
HEATRISK (AND SMALL POCKETS OF MAJOR HEATRISK) WILL OCCUR ON TUESDAY
WITH ONLY SLIGHTLY LOWER TEMPERATURES ON WEDNESDAY. THE TIMING AND
LOCATIONS OF A POTENTIAL HEAT ADVISORY FOR TUESDAY WILL BE MADE WITH
THE AFTERNOON UPDATE LATER TODAY. WHILE THE WARMER TEMPERATURES
PERSIST THROUGH THE AFTERNOON ON WEDNESDAY, AN UPPER LEVEL
DISTURBANCE OFF THE COAST OF SOCAL BEGINS TO LIFT NORTH TOWARD THE
CENTRAL COAST, BRINGING A LARGE PLUME OF MOISTURE ASSOCIATED WITH
TROPICAL STORM MARIO WITH IT. AS THE UPPER LEVEL LOW TRACKS
NORTH, WE'LL SEE AN INCREASE IN PWATS THAT CONTINUE TO APPROACH
200% OF NORMAL ON THURSDAY.
AS OF THIS UPDATE, THE BEST INITIAL WINDOW FOR ELEVATED DRY
THUNDERSTORMS APPEARS TO BE AFTER MIDNIGHT EARLY THURSDAY THROUGH
LATE THURSDAY MORNING, PRIMARILY ACROSS THE CENTRAL COAST IN
MONTEREY COUNTY AND SOUTHERN SAN BENITO COUNTY. MID-LEVEL LAPSE
RATES APPROACH 7C/KM WITH 30KTS OF SHEAR THURSDAY MORNING, HOWEVER
THERMAL INSTABILITY IS LIMITED WITH MUCAPE VALUES <100 J/KG AND SOME
CIN TO OVERCOME. THERE IS PLENTY OF TIME BETWEEN NOW AND THURSDAY
FOR THERMAL AND KINEMATIC INSTABILITY TO BETTER ALIGN. GIVEN THE
WARM AND DRY CONDITIONS OVER THE NEXT FEW DAYS LEADING INTO THE
POTENTIAL FOR ISOLATED ELEVATED CONVECTION EARLY THURSDAY INTO
FRIDAY, THE RISK FOR LIGHTNING INDUCED IGNITION AND RAPID FIRE
SPREAD IS CERTAINLY NON-ZERO AND SHOULD BE MONITORED CLOSELY BY
OUR PARTNERS. ALTHOUGH THURSDAY MORNING APPEARS TO BE THE BEST
WINDOW ATTM, CHANCES FOR ELEVATED CONVECTION CONTINUE INTO FRIDAY
AND FARTHER NORTH OVER A LARGER PORTION OF OUR FORECAST AREA.
WE'RE NOT EXPECTING A WIDESPREAD WETTING RAINFALL, WITH OVERALL
RAIN AMOUNTS NOT EXPECTED TO EXCEED A QUARTER OF AN INCH FOR THOSE
LOCATIONS THAT ARE FORTUNATE ENOUGH TO RECEIVE ANY RAIN AT ALL.
CHANCES FOR LIGHT SHOWERS CONTINUE INTO SATURDAY WITH LOW
CONFIDENCE IN THE SYNOPTIC PATTERN FOR SUNDAY AND BEYOND.
AVIATION
(12Z TAFS)
ISSUED AT 344 AM PDT MON SEP 15 2025
PATCHY STRATUS THIS MORNING LEADING TO LOCALIZED IFR AND FG ALONG
COASTAL AREAS. MARINE LAYER BECOMING VERY SHALLOW THROUGH TODAY
DUE TO LIGHT OFFSHORE FLOW AND BUILDING HIGH PRESSURE ALOFT. THIS
WILL AID IN QUICK CLEARING TO VFR THIS MORNING ACROSS MOST OF THE
AREA. SOME COASTAL TERMINALS MAY HOLD ON TO STRATUS A BIT LONGER,
BUT ANTICIPATING VFR ACROSS THE BOARD BY MID-MORNING. THIS SHALLOW
MARINE LAYER PATTERN PERSISTS THROUGH THE REST OF THE TAF PERIOD,
SO NOT EXPECTING ANY WIDESPREAD STRATUS TUESDAY MORNING. ONLY
LOCAL FG IMPACTS ALONG COASTAL AREAS.
VICINITY OF SFO...IFR CIGS AROUND THE BAY THIS MORNING WITH
INTERMITTENT IMPACTS AT THE TERMINAL. ANTICIPATED STRATUS TO MIX OUT
RATHER QUICKLY THIS MORNING DURING THE 17Z HOUR, THEN VFR THROUGH
THE REST OF THE TAF PERIOD.
SFO BRIDGE APPROACH...SIMILAR TO SFO.
MONTEREY BAY TERMINALS...PATCHY DENSE FG THIS MORNING THANKS TO A
COMPRESSED MARINE LAYER. EXPECTING THESE CONDITIONS TO LINGER INTO
THE 17Z HOUR BEFORE CLEARING TO VFR. ANOTHER ROUND OF PATCHY FG IS
POSSIBLE TONIGHT INTO TUESDAY MORNING, BUT LARGELY ANTICIPATING VFR
THROUGH THE REST OF THE PERIOD.
MARINE
(TODAY THROUGH SATURDAY)
ISSUED AT 344 AM PDT MON SEP 15 2025
WINDS CONTINUE TO SUBSIDE ACROSS THE WATERS THROUGH TODAY WHILE
FAIR WEATHER PERSISTS. MODERATE SEAS CONTINUE, ESPECIALLY
OFFSHORE, AND WILL SUBSIDE THROUGH MIDWEEK BEFORE BUILDING AGAIN
LATE WEEK. TROPICAL REMNANT MOISTURE IS ANTICIPATED TO ENTER THE
REGION BY MIDWEEK. ISOLATED SHOWERS AND THUNDERSTORMS ARE
POSSIBLE BEGINNING LATE WEDNESDAY THROUGH THURSDAY.
FIRE WEATHER
ISSUED AT 139 PM PDT SUN SEP 14 2025
THE FIRE WEATHER THREAT WILL ELEVATE THIS WEEK FOR A FEW REASONS.
1) DESPITE LAST WEEKS PRECIPITATION, OUR AREA HAS NOT HAD A SEASON
ENDING RAINFALL EVENT. 2) WHILE ENERGY RELEASE COMPONENTS (ERCS)
HAVE REBOUNDED SIGNIFICANTLY, THE ABOVE NORMAL MAXTS AND MINTS
WILL SERVE TO RAPIDLY CURE SOME OF THE FINER FUELS AND
SUBSEQUENTLY ERC VALUES WILL SUPPORT SOME FIRE SPREAD. THE ABOVE
NORMAL WARMTH WILL ALSO TRANSLATE TO POOR OVERNIGHT HUMIDITY
RECOVERY (RH BELOW 35%) ACROSS THE MAYACAMAS, SANTA CRUZ
MOUNTAINS, AS WELL AS THE DIABLO, SANTA LUCIA, AND GALIBAN RANGES
THIS WEEK. AFTERNOON RH WILL ALSO FALL INTO THE 20-35% RANGE FOR
MOST AREAS, EXCEPT ALONG THE IMMEDIATE COAST. 3) THERE IS AN
OPPORTUNITY FOR ISOLATED THUNDERSTORMS AS EARLY AS THURSDAY AND
INTO FRIDAY. THE AREAS WITH THE GREATEST CHANCES (AROUND 20-25%)
FOR ISOLATED THUNDERSTORMS, ARE ACROSS THE CENTRAL COAST, EASTERN
SANTA CLARA HILLS, AND EAST BAY. AT THIS TIME, RAIN AMOUNTS ARE
ANTICIPATED TO REMAIN LARGELY BELOW ONE-TENTH OF AN INCH AND AS A
RESULT, IGNITIONS DUE TO DRY LIGHTNING MAY TRANSPIRE THURSDAY AND
INTO FRIDAY.
MTR WATCHES/WARNINGS/ADVISORIES
CA...NONE.
PZ...SMALL CRAFT ADVISORY UNTIL 3 PM PDT THIS AFTERNOON FOR PT ARENA
TO PT REYES 10-60 NM.
SHORT TERM...JM
LONG TERM....JM
AVIATION...BEHRINGER
MARINE...BEHRINGER
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