380
FXUS66 KMTR 181027 CCA
AFDMTR
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SAN FRANCISCO CA
313 AM PDT THU SEP 18 2025
..NEW SHORT TERM, LONG TERM, MARINE
KEY MESSAGES
UPDATED AT 304 AM PDT THU SEP 18 2025
- SHOWERS WITH ISOLATED TO SCATTERED THUNDERSTORMS TODAY INTO
FRIDAY
- COOLER TEMPERATURES TODAY AND FRIDAY, WITH A WEEKEND WARM UP
- RAINFALL CHANCES INCREASE AGAIN FOR THE BEGINNING OF NEXT WEEK
SHORT TERM
ISSUED AT 304 AM PDT THU SEP 18 2025
(TODAY AND TONIGHT)
FORECAST FOR AREAS OF SHOWERS AND THUNDERSTORMS CONTINUING TO MOVE
NORTH INTO OUR AREA OUT AHEAD OF THE REMNANTS OF MARIO REMAINS ON
TRACK AS WE HEAD INTO EARLY THURSDAY MORNING. MARIO IS A LOOSELY
DEFINED UPPER LEVEL DISTURBANCE AT THIS POINT, CURRENTLY MOVING
SLOWLY NORTH OFFSHORE OVER THE WATERS OF SOCAL. THE HEAVIEST
RAINFALL AS OF 3AM PDT IS OVER THE CHANNEL ISLANDS WITH THE
LEADING EDGE OF THE PRECIP JUST SOUTH OF PASO ROBLES. LIGHT TO
OCCASIONALLY MODERATE SHOWERS OFFSHORE OF OUR AREA, ASSOCIATED
WITH AN UPPER LEVEL DISTURBANCE OUT AHEAD OF MARIO WILL CONTINUE
TO DRIFT NORTHWEST OVER OUR OPEN WATERS FOR THE REMAINDER OF THE
MORNING.
ISOLATED TO SCATTERED THUNDERSTORMS REMAIN IN THE FORECAST,
ESPECIALLY FOR LATER THIS AFTERNOON AND EVENING, HOWEVER THE TREND
FOR ENOUGH INSTABILITY FOR IMPACTFUL CONVECTION HAS BEEN STEADILY
DECLINING. THE GOOD NEWS IS THAT, THE UNUSUALLY HIGH PWATS (NEAR
RECORD FOR THIS TIME OF YEAR) MAY LEAD TO SOME WELCOMED WETTING
RAINFALL ACROSS MUCH OF THE CENTRAL COAST, AND PORTIONS OF THE SOUTH
BAY AND EAST BAY. GUIDANCE HAS STRUGGLED WITH THE POSITION OF MARIO
THE PAST FEWS DAYS LEADING UP TO ITS ARRIVAL ON OUR SOUTHERN
DOORSTEP THIS MORNING, WITH NO DOMINANT SYNOPTIC FEATURE FORCING ITS
PROGRESS. DETERMINISTIC GUIDANCE BOTH HIRES AND SYNOPTIC SCALE,
INDICATE A MORE EASTERN PROJECTION INLAND THAN THIS TIME 24HRS AGO,
AND THAT TREND IS INDICATED WITHIN THE NATIONAL BLEND OF MODELS
(NBM).
THE BEST WINDOW FOR ISOLATED TO SCATTERED THUNDERSTORMS IS THIS
AFTERNOON AND EVENING, MAINLY ACROSS THE CENTRAL COAST AND SOUTH
BAY. BOTH THERMAL AND KINEMATIC INSTABILITY HAS WEAKENED WITH MOST
RECENT CAM UPDATES. ENSEMBLE MEAN CAMS MUCAPE (MOST UNSTABLE
CONVECTIVE AVAILABLE POTENTIAL ENERGY) VALUES ARE GENERALLY LESS
THAN 100J/KG, WITH WORST-CASE VALUES STRUGGLING TO ECLIPSE
200J/KG. MEANWHILE DCAPE (DOWNDRAFT CONVECTIVE AVAILABLE POTENTIAL
ENERGY) VALUES ARE GENERALLY 4-5X HIGHER. THAT MEANS THAT THE
STRONGEST UPDRAFTS AREN'T LIKELY TO LAST LONG, AND THOSE THAT DO
ARE MORE LIKELY TO PRODUCE MODERATE TO STRONG WIND GUSTS (BUT LESS
THAN 50MPH) AS THEY COLLAPSE. ANY CLOUD-TO-GROUND LIGHTNING OVER
A DRY AREA CONTINUES TO POSE A FIRE WEATHER THREAT, AND CONVERSELY
WHERE IT DOES RAIN, BRIEF DOWNPOURS ARE POSSIBLE. OTHERWISE
BENEFICIAL WETTING RAINFALL WILL BE THE STORY FOR A MAJORITY OF
OUR AREA BETWEEN NOW AND FRIDAY MORNING. PORTIONS OF SOUTHERN
MONTEREY COUNTY IN THE SANTA LUCIAS MAY SEE OVER AN INCH OF RAIN
OVER THE NEXT 24 HOURS OR SO, WITH A 0.25-0.50" FARTHER INLAND INTO
SAN BENITO COUNTY. ELEVATED AREAS FARTHER INLAND ACROSS THE SOUTH
BAY AND EAST BAY MAY SEE UP TO A 0.25" WITH THE BAY AREA AND NORTH
BAY LUCKY TO REACH 0.10" OVER THAT SAME TIME FRAME.
LONG TERM
ISSUED AT 304 AM PDT THU SEP 18 2025
(FRIDAY THROUGH WEDNESDAY)
ONCE THE MOSTLY BENEFICIAL WETTING RAINFALL IS REALIZED THROUGH
THE REMAINDER OF FRIDAY WE'LL SEE TEMPERATURES WARM UP OVER THE
WEEKEND INTO MONDAY. WHILE WE WARM UP OVER THE WEEKEND, EXTENDED
GUIDANCE SHOWS AN UPPER LEVEL DISTURBANCE WELL OFFSHORE DIVING
SOUTH FROM THE PACIFIC NORTHWEST DOWN TO SOCAL, BECOMING ALMOST
STATIONARY SUNDAY INTO MONDAY, THEN TAKING AIM ONCE AGAIN FOR THE
CENTRAL COAST ON TUESDAY WITH MORE WETTING RAIN LIKELY WITH THAT
SYSTEM. WE'RE FORTUNATE TO BE SEEING THIS RAINFALL AT THIS TIME OF
THE YEAR.
AVIATION
(06Z TAFS)
ISSUED AT 957 PM PDT WED SEP 17 2025
MAIN DIFFERENCE FROM 00Z TAFS WAS TO ADJUST RAIN CHANCES (DECREASING
THEM) FOR AIRPORTS ACROSS THE BAY AREA AND SHIFT HIGHER POTENTIAL
FOR RAIN SHOWERS FURTHER SOUTH OVER THE CENTRAL COAST. STILL SOME
UNCERTAINTY AS TO WHERE SHOWERS AND THUNDERSTORMS WILL SET UP
TOMORROW SO THIS IS LIKELY TO BE FURTHER REFINED IN FUTURE TAF
ISSUANCES. CONTINUING TO LEAN TOWARDS TROPICAL MOISTURE AND SHOWERS
DISRUPTING THE MARINE LAYER TONIGHT WHICH WILL KEEP VFR CONDITIONS
AT INTERIOR SITES. FOR HAF, MRY, AND SNS - DELAYED THE ARRIVAL OF
IFR CONDITIONS UNTIL LATER TONIGHT WHICH ALIGNS BETTER WITH GFSLAMP
PROBABILISTIC GUIDANCE. CONFIDENCE REMAINS ON THE LOWER SIDE THAT
IFR CIGS WILL DEVELOP ALONG THE COAST GIVEN THE DISRUPTIONS TO THE
MARINE LAYER FROM SHOWERS AND TROPICAL MOISTURE. ELEVATED POTENTIAL
FOR THUNDERSTORMS TOMORROW CONTINUES WITH MRY AND SNS THE TWO MOST
LIKELY TO SEE THUNDERSTORM ACTIVITY. WINDS LOOK TO PICK UP EARLY
TOMORROW MORNING AND WILL REMAIN BREEZY THROUGH THE
AFTERNOON/EVENING HOURS.
VICINITY OF SFO...VFR THROUGH TAF PERIOD. MODEL GUIDANCE REMAINS
MORE BULLISH AS TO THE INLAND EXTENT OF IFR-MVFR STRATUS OVERNIGHT
AND SHOWS SOME POTENTIAL FOR CIGS BETWEEN 12-16Z AT SFO. CONFIDENCE
IS LOW IN THAT SCENARIO WITH CURRENT THINKING LEANING TOWARDS
OVERCAST HIGH CLOUDS AND POTENTIALLY A FEW LOW LEVEL CLOUDS
DEVELOPING EARLY THURSDAY MORNING. GUIDANCE HAS BACKED OFF ON
SHOWERS IN THE VICINITY OF SFO EARLY THURSDAY MORNING BUT REMAIN
ELEVATED DURING THE AFTERNOON AND EVENING HOURS. LOW CONFIDENCE THAT
A THUNDERSTORM WILL DEVELOP IN THE VICINITY OF SFO OR DIRECTLY
IMPACT THE AIRPORT.
SFO BRIDGE APPROACH...SIMILAR TO SFO.
MONTEREY BAY TERMINALS...SHOWERS REMAIN IN THE VICINITY OF MRY AND
ARE EXPECTED TO CONTINUE OVERNIGHT. SHOWERS WILL BECOME MORE
WIDESPREAD ACROSS THE CENTRAL COAST BY THURSDAY MORNING AND CONTINUE
INTO THE EVENING. GUIDANCE SUGGESTS SOME POTENTIAL FOR TRAINING
THUNDERSTORMS IN THE VICNITY OF MRY AND SNS TO BEGIN LATE THURSDAY
EVENING AND CONTINUE THROUGH EARLY FRIDAY MORNING. MODEL GUIDANCE
HAS NOT BEEN CONSISTENT AS TO WHERE THESE TRAINING THUNDERSTORMS
WILL SET UP SO CONFIDENCE IS LOW TO MODERATE IN THIS OUTCOME.
ADJUSTED THE ARRIVAL OF IFR CIGS TONIGHT BACK BY A FEW HOURS AT MRY
AND SNS WITH LOW TO MODERATE CONFIDENCE IN TIMING OF STRATUS
RETURN.
MARINE
(TODAY THROUGH TUESDAY)
ISSUED AT 304 AM PDT THU SEP 18 2025
STRONG NORTHERLY WINDS, OCCASIONAL GALE FORCE GUSTS, AND VERY
ROUGH SEAS WILL PREVAIL FOR THE NORTHERN OUTER WATERS TODAY.
ELSEWHERE, A MODERATE NORTHERLY BREEZE AND MODERATE TO ROUGH SEAS
WILL PREVAIL. ISOLATED RAIN SHOWERS WITH EMBEDDED THUNDERSTORMS
REMAIN POSSIBLE TODAY WHICH WILL POSE THE RISK OF LIGHTNING,
LOCALLY HEAVY RAINFALL, AND ERRATIC GALE FORCE GUSTS. CONDITIONS
IMPROVE TOMORROW AS WINDS DIMINISH, SEAS ABATE, AND UNSETTLED
WEATHER EXITS THE REGION.
FIRE WEATHER
ISSUED AT 813 PM PDT WED SEP 17 2025
THREAT FOR DRY LIGHTNING IS DIMINISHING AS DEEPER TROPICAL
MOISTURE MOVES IN FROM THE SOUTH. THUNDERSTORM CHANCES ARE
UNCERTAIN THURSDAY AFTERNOON ACROSS THE CENTRAL COAST.
THUNDERSTORMS THAT FORM OVER THE SANTA LUCIA MAY EXPERIENCE DRY
AIR ENTRAINMENT DUE TO STRONG OFFSHORE WINDS OFF THE GABILAN
RANGE. DEEP MOISTURE WILL STILL BE IN PLACE, SO THIS ISN'T A
TYPICAL "OFFSHORE WIND EVENT", BUT MAY BE JUST ENOUGH TO SNUB MUCH
OF THE THUNDERSTORM ACTIVITY ACROSS THE CENTRAL COAST. HOWEVER,
THIS IS ALL DEPENDENT ON THE TRACK OF THE LOW AND IF IT SHIFTS
EASTWARD. FOR THE REST OF THE REGION, ISOLATED THUNDERSTORM
ACTIVITY WILL SPREAD NORTHWARD THROUGH THURSDAY NIGHT INTO FRIDAY
MORNING. EVEN THOUGH MOST THUNDERSTORM CORES WILL PRODUCE WETTING
RAIN, THERE IS ALWAYS THE CHANCE OF A STRAY STRIKE OR TWO OUTSIDE
OF THE MAIN CORE, IN ADDITION TO GUSTY AND ERRATIC WINDS.
BEHRINGER
MTR WATCHES/WARNINGS/ADVISORIES
CA...NONE.
PZ...SMALL CRAFT ADVISORY UNTIL 9 AM PDT FRIDAY FOR PT ARENA TO PT
REYES 10-60 NM.
SMALL CRAFT ADVISORY UNTIL 9 AM PDT THIS MORNING FOR PIGEON PT
TO PT PINOS 10-60 NM.
SHORT TERM...JM
LONG TERM....JM
AVIATION...KENNEDY
MARINE...SARMENT
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