983
FXUS66 KMTR 151736
AFDMTR
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SAN FRANCISCO CA
1036 AM PDT MON SEP 15 2025
..NEW 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
UPDATE
ISSUED AT 907 AM PDT MON SEP 15 2025
NEAR TERM WEATHER CONCERNS WERE FOCUSED ON PATCHY DENSE FOG
IMPACTING A SMALL AREA ALONG COASTLINE FROM HALF MOON BAY
SOUTHWARD TO BIG SUR, INCLUDING MONTEREY BAY REGION. A FEW
SENSORS AND CAMS SHOWED DENSE FOG BEING REPORTED. THAT BEING SAID,
RECENT TRENDS ARE ALREADY SHOWING RAPID IMPROVEMENT. IN FACT,
LATEST SATELLITE SHOWS SOME WEAK LOW LEVEL OFFSHORE FLOW KICKING
IN, WHICH IS "PEELING" THE CLOUDS OFF THE COASTLINE AND INTO THE
COASTAL WATERS.
CURRENT FORECAST LOOKS ON TRACK.
FINE TUNING TWO IMPACTFUL SCENARIOS WITH AFTERNOON FORECAST:
HEATRISK CONCERNS MONDAY THROUGH WEDNESDAY WITH INTERIOR TEMPS IN
THE 90S TO NEAR 100. ADDITIONALLY, TROPICAL MOISTURE SURGING
NORTHWARD AS EARLY AS WEDNESDAY AFTERNOON/EVENING. IMPACTS WOULD
BE LIGHTNING AND POTENTIAL FIRE WEATHER CONCERNS.
MM
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
(18Z TAFS)
ISSUED AT 1034 AM PDT MON SEP 15 2025
VFR CONDITIONS HAVE RETURNED TO ALL TAF SITES THIS MORNING AND ARE
LIKELY TO REMAIN THAT WAY THROUGH MUCH OF THE AFTERNOON AND EVENING.
HOWEVER, COASTAL SITES SUCH AS KHAF REMAIN SUB-IFR BUT ARE FORECAST
TO SCATTERED OUT BY AROUND 19Z. THE MARINE LAYER WILL REMAIN SHALLOW,
GENERALLY LESS THAN 500 FEET IN DEPTH WITH MODERATE TO HIGH
CONFIDENCE FOR FOG/LOW CEILINGS TO IMPACT COASTAL AREAS SUCH AS
KMRY, KSNS, AND KHAF THIS EVENING AND CONTINUING INTO TUESDAY
MORNING. FOR THE BAY AREA TERMINALS, LOOKING FOR THE POTENTIAL FOR A
FEW HOURS EARLY TUESDAY MORNING FOR IFR CONDITIONS, MODERATE
CONFIDENCE. ANY LOW CEILINGS OR VISIBILITIES WILL CLEAR BY AROUND
15Z-17Z TUESDAY AND WILL RETURN TO VFR.
VICINITY OF SFO...VFR. ONSHORE WINDS ARE FORECAST TO INCREASE THIS
AFTERNOON BEFORE BECOMING LIGHT/VARIABLE EARLY TUESDAY MORNING.
MODERATE CONFIDENCE FOR IFR CEILINGS TO DEVELOP OVER THE TERMINAL
BETWEEN 12Z-16Z TUESDAY BEFORE VFR CONDITIONS RETURN AND ONSHORE
WINDS INCREASE.
SFO BRIDGE APPROACH...SIMILAR TO SFO.
MONTEREY BAY TERMINALS...VFR. ONSHORE WINDS ARE FORECAST TO INCREASE
THIS AFTERNOON BEFORE EASING AFTER SUNSET. THERE IS MODERATE TO HIGH
CONFIDENCE FOR IFR CEILINGS/VISIBILITIES TO RETURN THIS EVENING AND
LOWER TO LIFR LATE IN THE NIGHT AND INTO TUESDAY MORNING.
MARINE
(TODAY THROUGH SATURDAY)
ISSUED AT 1034 AM PDT MON SEP 15 2025
WINDS CONTINUE TO DIMINISH 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 GABILAN 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.
BAIN
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...RGASS
MARINE...RGASS
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