984
FXUS66 KMTR 201615
AFDMTR
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SAN FRANCISCO CA
915 AM PDT TUE OCT 20 2026
..NEW UPDATE, MARINE
KEY MESSAGES
UPDATED AT 1200 PM PDT MON OCT 19 2026
- COOLING TREND CONTINUES THROUGH THE END OF THE WEEK
- BENEFICIAL LIGHT RAIN SHOWERS EXPECTED MID-WEEK
- THUNDERSTORMS POSSIBLE MID-WEEK ACROSS SOUTHERN CENTRAL COAST
UPDATE
ISSUED AT 856 AM PDT TUE OCT 20 2026
LOOKING OUT THE WINDOW, YES SOMETIMES WE DO JUST LOOK OUT THE
WINDOW, WE CAN SEE CIRRUS AND EVEN SOME ACCAS. BOTH OF THESE CLOUD
TYPES CAN BE PRECURSORS TO A PATTERN CHANGE. IF WE TAKE A BROADER
LOOK AT SATELLITE THE BANDS OF CLOUDS CURRENTLY WEST OF MONTEREY
ARE THE LEADING EDGE OF AN OCCLUDED LOW PRESSURE PARKED OFF THE
COAST. ADDITIONALLY, THE BANDS EAST OF MONTEREY ARE LIKELY TIED
TO THE POSITION OF AN UPPER LEVEL JET (GOES WEST SHOWS STRONG
WINDS IN THE 250-450MB RANGE). THE ACCAS CAN BE A GOOD INDICATOR
OF MOISTURE AND LOWER-MID LEVEL INSTABILITY. IF YOU HAVEN'T
NOTICED, KMUX IS STILL IN PRECIP MODE. WE ARE NOW PICKING UP A FEW
ECHOES WELL OFFSHORE CLOSER TO THE LOW PRESSURE AND SURFACE
BOUNDARIES.
NO CHANGES IN THE NEAR TERM FORECAST FOR TODAY. WILL BE FOCUSING
ON THE NEXT 24-48 HOUR AS THE OFFSHORE SYSTEM MOVES EAST BRINGING
DYNAMICS WITH IT. EARLY LOOK STILL SUGGEST SOME PRECIP ACROSS THE
ENTIRE CWA. THE BIGGEST IMPACTS WILL BE TIED TO THE POTENTIAL
CONVECTIVE THREAT ALONG THE CENTRAL COAST. WILL COORDINATE WITH
SPC TO ANY UPDATES ON SVR OUTLOOKS. STILL LOOKS LIKE A LOW CHC FOR
SOME ROTATING CELLS TO DEVELOP OVER THE COASTAL WATERS OFF BIG SUR
WEDNESDAY.
MM
SHORT TERM
ISSUED AT 1203 AM PDT TUE OCT 20 2026
(TODAY THROUGH WEDNESDAY)
THE LOW PRESSURE SYSTEM IS ALREADY MAKING ITS PRESENCE KNOWN AS IT
NEARS OUR COAST. NOT ONLY WERE THERE VARIOUS CLOUD LAYERS PRESENT ON
MONDAY, BUT SOME MEASURABLE RAINFALL HAS BEEN OBSERVED IN
NORTHERN CALIFORNIA NEARBY EUREKA (AS OF 10 PM PDT MONDAY). GIVEN
THAT THE CENTER OF THE LOW IS STILL TO OUR NORTHWEST, THESE
RAINBANDS ARE NOT EXPECTED TO IMPACT US JUST YET...
OVERNIGHT, THE UPPER-LEVEL TROUGH CONTINUES TO DIG SOUTHWARD ALONG
THE COAST AND BECOMES FULLY CUT-OFF FROM THE MAIN AIRFLOW BY
TUESDAY. DURING THE DAY, CALM CONDITIONS ARE EXPECTED WITH BELOW
NORMAL TEMPERATURES AND INFREQUENT WIND GUSTS UP TO 20-25 MPH.
LATER TONIGHT, THE CUT-OFF LOW BEGINS TO SLOWLY PROPAGATE
EASTWARD WITH THE FIRST FEW RAINBANDS POSSIBLY IMPACTING THE
SOUTHERN CENTRAL COAST FIRST. THROUGH THE OVERNIGHT HOURS, THESE
RAINBANDS BEGIN TO MAKE THEIR WAY ACROSS THE REST OF THE CENTRAL
COAST AND BAY AREA.
RAIN CHANCES INCREASE WEDNESDAY WITH THE NORTH AND EAST BAY LESS
LIKELY TO EXPERIENCE WETTING RAIN (>0.10 INCH) DURING THE EVENT.
CHANCES FOR WETTING RAIN INCREASE TOWARDS THE CENTRAL COAST WHERE
THE CENTER OF THE CUT-OFF LOW IS EXPECTED TO ENHANCE MOISTURE
TRANSPORT ONSHORE. THE EASTERN PORTION OF THE SYSTEM IS FORECAST TO
HAVE STRONGER WIND SPEEDS THAN THE WESTERN PORTION, LIKELY DUE TO A
TIGHTER PRESSURE GRADIENT DOWNSTREAM AS WELL AS A SURGE IN MOMENTUM
FLUX FROM THE SUBTROPICAL JET STREAM. THIS ROUGHLY COINCIDES WITH
WHERE THE MOST MOISTURE, INSTABILITY, AND LIFT CAN BE FOUND. AS A
RESULT, THUNDERSTORM POTENTIAL (<20%) REMAINS THE GREATEST ALONG THE
CENTRAL COAST. THE EXACT TIMING IS UNCERTAIN, THOUGH MODEL GUIDANCE
IS SUGGESTING THE HIGHEST PROBABILITIES ARE DURING WEDNESDAY
AFTERNOON. MOST UNSTABLE CAPE HAS TRENDED SLIGHTLY DOWNWARD COMPARED
TO YESTERDAY, THOUGH IT IS STILL HIGHLIGHTING THE BIG SUR COASTLINE.
THE LATEST SPC CONVECTIVE OUTLOOK HAS UPGRADED CENTRAL AND SOUTHERN
CALIFORNIA TO A MARGINAL SEVERE THUNDERSTORM RISK, JUST SOUTH OF THE
MONTEREY COUNTY BORDER... EVEN THOUGH WE ARE NOT INCLUDED IN THE
MARGINAL SEVERE RISK, THIS IS TOO CLOSE TO COMFORT CONSIDERING THE
PROXIMITY TO THE TIMBER AND PLASKETT FIRE BURN SCARS. AS THE EVENT
DRAWS CLOSER, THIS WILL BE AN AREA OF SPECIAL INTEREST NOT ONLY FOR
THE POTENTIAL OF DEBRIS FLOWS IF RAINFALL THRESHOLDS ARE MET, BUT
ALSO GUSTY AND ERRATIC WINDS THAT MAY RESULT FROM LOW-TOPPED
THUNDERSTORMS.
LONG TERM
ISSUED AT 1203 AM PDT TUE OCT 20 2026
(WEDNESDAY NIGHT THROUGH MONDAY)
OVERNIGHT, THE CENTER OF THE LOW GRADUALLY MOVES ACROSS THE REGION
RESULTING IN DIMINISHING RAINFALL CHANCES, THOUGH THE CENTRAL COAST
STILL REMAINS WITH A 60-80%. LINGERING RAIN SHOWERS PERSIST THROUGH
THURSDAY AS THE SYSTEM CONTINUES ITS EASTWARD TRACK. ACROSS THE BAY
AREA, 20-40% RAIN CHANCES PERSIST WITH A 40-60% CHANCE ACROSS THE
CENTRAL COAST.
BY FRIDAY, THE TROUGH CENTER WILL BE EAST OF OUR AREA AS HIGH
PRESSURE GRADUALLY BUILDS IN ITS WAKE WITH A MEAN NORTHERLY WIND
FLOW. TO BALANCE OUT THE RECENT DISTURBANCE, A SLIGHTLY WARMER AND
DRIER AIR MASS SETTLES OVER THE REGION THIS WEEKEND WITH SEASONAL
TEMPERATURES IN THE 60S AND 70S.
AVIATION
(12Z TAFS)
ISSUED AT 419 AM PDT TUE OCT 20 2026
VFR THROUGH THE TAF PERIOD. HIGH CLOUDS REMAIN OVER THE AREA
THROUGHOUT TODAY WITH CEILINGS GRADUALLY LOWERING TOMORROW AS
SHOWERS APPROACH. WINDS ARE LIGHT THIS MORNING WITH MODERATE
ONSHORE WINDS EXPECTED DURING THE AFTERNOON AND EVENING. WINDS
THEN DIMINISH TONIGHT OVERNIGHT BECOMING SOUTHERLY TO VARIABLE.
RAIN SHOWERS ARRIVE AROUND 12Z TOMORROW MORNING SO HAVE STARTED
MENTIONING SHOWER POTENTIAL FOR OAK AND SFO WHILE THIS IS STILL
OUTSIDE OF THE CURRENT TAF PERIOD FOR NON 30 HOUR TAF SITES.
SHOWERS WILL REACH THE CENTRAL COAST FIRST BEFORE SPREADING
NORTHWARDS INTO THE BAY AREA BY LATE MORNING. EXPECT SHOWER
ACTIVITY TO PICK UP AT MRY AND SNS SHORTLY AFTER 12Z TOMORROW
WITH THE BAY AREA SITES FOLLOWING SUITE BETWEEN 12-18Z.
VICINITY OF SFO...VFR. WINDS ARE LIGHT AND SOUTHERLY THIS MORNING
WITH MODERATE ONSHORE WINDS (12 KNOTS) THIS AFTERNOON/EVENING.
WINDS DECREASE OVERNIGHT TONIGHT BECOMING VARIABLE. SHOWER
CHANCES INCREASE WEDNESDAY MORNING WITH LIGHT SHOWERS BECOMING
MORE LIKELY AFTER 12Z. SHOWER ACTIVITY WILL THEN PICKUP WEDNESDAY
AFTERNOON WITH REDUCTIONS IN CEILINGS AND VISIBILITIES LIKELY AS
HEAVIER SHOWERS DEVELOP.
SFO BRIDGE APPROACH...SIMILAR TO SFO.
MONTEREY BAY TERMINALS...VFR. LIGHT SOUTHERLY WINDS CONTINUE
THROUGH LATE MORNING BEFORE MODERATE W TO NW WINDS RETURN THIS
AFTERNOON AND EVENING. WINDS DECREASE OVERNIGHT BECOMING SOUTHERLY
TO VARIABLE. CURRENT MODEL GUIDANCE SHOWS SHOWERS APPROACHING THE
CENTRAL COAST AROUND 12Z TOMORROW MORNING. EXPECT TEMPORARY
REDUCTIONS IN VISIBILITY AND CEILING HEIGHTS AS STRONGER SHOWERS
DEVELOP AND MOVE INLAND. MODERATE SHOWERS BECOME MORE WIDESPREAD
BY THE AFTERNOON AS THE BULK OF THE RAIN MOVES IN.
MARINE
(TODAY THROUGH SUNDAY)
ISSUED AT 856 AM PDT TUE OCT 20 2026
A STORM SYSTEM OFF THE CALIFORNIA COAST WILL KEEP LIGHT TO GENTLE
SOUTHERLY BREEZE THROUGH EARLY THURSDAY WITH WINDS GRADUALLY
BECOMING MORE NORTHERLY WEDNESDAY INTO THURSDAY. FRESH TO STRONG
NORTHERLY WINDS RETURN THURSDAY AND CONTINUE INTO THE WEEKEND WITH
NEAR GALE FORCE GUSTS POSSIBLE ACROSS THE NORTHERN OUTER WATERS.
MODERATE SEAS PREVAIL WITH LOCALIZED ROUGH SEAS ACROSS THE OUTER
WATERS TUESDAY AND FRIDAY. RAIN SHOWERS WITH A CHANCE OF
THUNDERSTORMS ARE EXPECTED LATE TUESDAY THROUGH THURSDAY,
ESPECIALLY SOUTH OF PIGEON POINT.
MTR WATCHES/WARNINGS/ADVISORIES
CA...NONE.
PZ...NONE.
SHORT TERM...NAVARRETE
LONG TERM....NAVARRETE
AVIATION...KENNEDY
MARINE...MM
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