204
FXUS66 KMTR 122149
AFDMTR
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SAN FRANCISCO CA
249 PM PDT TUE AUG 12 2025
..NEW SHORT TERM, LONG TERM
KEY MESSAGES
UPDATED AT 320 AM PDT TUE AUG 12 2025
- MODERATE HEATRISK TODAY FOR PORTIONS OF INTERIOR MONTEREY AND SAN
BENITO COUNTIES.
- ELEVATED FIRE WEATHER CONCERNS PERSIST THROUGH WEDNESDAY FOR THE
INTERIOR CENTRAL COAST.
- PATTERN CHANGE TODAY, WITH MORE WIDESPREAD COOLING AND COASTAL
CLOUDS AND DRIZZLE STARTING WEDNESDAY.
SHORT TERM
ISSUED AT 153 PM PDT TUE AUG 12 2025
(THIS EVENING THROUGH WEDNESDAY)
HIGHLIGHTS THROUGH THE SHORT TERM HAVEN'T CHANGED THAT MUCH FROM
THE PREVIOUS FORECAST: PATTERN CHANGE IS OCCURING, COOLDOWN ON THE
WAY, NIGHT/MORNING MARINE LAYER REMAINS, EYEING MOISTURE OFF THE
CA MOISTURE.
LET'S LOOK INTO THE DETAILS. THE LONGWAVE UPPER RIDGE THAT
BROUGHT HEAT IS FADING QUICK AS AN UPPER TROUGH IS SETTLING YET
AGAIN OVER THE WEST. THE DETAILS ARE VERY NUANCED, ESPECIALLY
WHEN IT COMES TO EYEING THE MOISTURE TRACKING UP THE COAST. THAT
IS THE BUST PORTION OF THE FORECAST. THE UPPER LEVEL MOISTURE
LURKING OFF SOCAL IS THE LEFTOVERS OF TS IVO. THE LEADING EDGE OF
THIS MOISTURE IS ALREADY BEING SEEN ON THE SATELLITE IN THE WAY OF
HIGH BASED CU. RADARS ARE EVENING PICKING UP A FEW RETURNS HIGH
UP THIS AFTERNOON. THE KEY HERE IS THE MOISTURE IS PRETTY HIGH
UP. WHILE ONE CAN SEE IT ON MODEL DATA FROM 700-500MB LAYER IT'S
BETTER SEEN SLIGHTLY HIGHER AT 500-300MB. MEANING, FROM A HIGH
BASED TSTORM INGREDIENT IT'S JUST A TAD HIGHER THAN IDEAL. HOW
ABOUT FORCING? LAPSE RATES ARE PRETTY SOLID TONIGHT AND WEDNESDAY
WITH POCKETS OF MUCAPE. THESE LAPSE RATES ARE ALSO BEING AIDED BY
A WEAK SHORTWAVE TROUGH RIDING THE WESTERN EDGE OF THE DEPARTING
HIGH. ADDITIONALLY, THE 1.5 PVU PRESSURE SURFACE ALSO SHOWS A
RIPPLE ALOFT. FWIW PV SURFACES, IT'S A GREAT WAY TO SEE SUBTLE
DYNAMIC TROPOPAUSE LIFTING/ASCENT FEATURES ALOFT. WHAT ABOUT
OVERALL FLOW? THAT'S THE REAL KICKER. WHILE WE HAVE SOME MOISTURE
(NOT IDEAL) AND UPPER LEVEL INSTABILITY, IT'S THE FLOW ALOFT THAT
WILL LIKELY BE THE SHOW STOPPER FOR THUNDERSTORMS. FLOW IS MORE
WEST-EAST (ZONAL) AND NOT EQUATOR-POLE (MERIDIONAL). WHILE
MOISTURE ALOFT DOES ADVECT NORTH, THE FLOW QUICKLY TURNS ZONAL
AHEAD OF THE MOISTURE INFLUX ALMOST BLOCKING ITS NORTHWARD PUSH.
THEREFORE, STILL FEEL COMFORTABLE NOT MENTIONING THUNDERSTORMS IN
THE FORECAST. A PASSING SHOWER OR SOME VIRGA SEEMS MORE
REASONABLE. A SLIGHTLY DEVIATION IN THE ZONAL FLOW TIMING OR
STRENGTH WILL CHANGE THE OUTCOME. FINALLY, PROBABILISTIC GUIDANCE
AND CALIBRATED LIGHTNING FORECASTS BOTH SHOW NO CONVECTION
EITHER. REGARDLESS IT WILL BE INTERESTING WATCH THE EVOLUTION.
LONG TERM
ISSUED AT 240 PM PDT TUE AUG 12 2025
(WEDNESDAY NIGHT THROUGH NEXT MONDAY)
THE COOLDOWN NOTED FROM WEDNESDAY WILL CONTINUE THURSDAY AND THEN
LINGER INTO THE UPCOMING WEEKEND. ONE OF THE BIGGER WEATHER
IMPACTS FOR THE LONG TERM WILL BE INCREASING ONSHORE FLOW AND
SUBSEQUENT WINDS ON FRIDAY INTO SATURDAY. WINDS INITIALLY RAMP UP
OVER THE WATERS FRIDAY AND THEN SPREAD INLAND FRIDAY EVENING AND
EARLY SATURDAY, ESPECIALLY INLAND GAPS/PASSES.
AVIATION
(18Z TAFS)
ISSUED AT 1055 AM PDT TUE AUG 12 2025
MIX BAG OF IFR/MVFR CONDITIONS LINGERING THIS MORNING ACROSS MUCH OF
THE REGION, ESPECIALLY IN PLACES CLOSE TO THE BAYS AND THE COAST.
IMPROVING CONDITIONS ARE OCCURING AT INLAND TAF SITES WITH LOW
CLOUDS SCATTERING OUT AND/OR CLEARING BY LATE THIS MORNING, THE
EXCEPTION BEING HAF WHERE LOW CEILINGS WILL LIKELY PREVAIL. ONSHORE
WINDS WILL INCREASE ONCE AGAIN THIS AFTERNOON BEFORE EASING AFTER
SUNSET AROUND THE MONTEREY BAY TERMINALS AND OVERNIGHT ACROSS THE
BAY AREA TERMINALS. THERE IS HIGH CONFIDENCE FOR BOTH THE MONTEREY
BAY AND SAN FRANCISCO BAY TERMINALS TO SEE AN EARLY RETURN OF
LIFR/IFR/MVFR CEILINGS THIS EVENING THAT WILL PERSIST THROUGH MID-
MORNING ON WEDNESDAY.
VICINITY OF SFO...VFR AT SFO. MVFR AT OAK. EXPECTING CEILINGS TO
LIFT TO VFR WITHIN THE NEXT FEW HOURS, BUT ONLY BRIEFLY. ONSHORE
WINDS INCREASE ONCE AGAIN THIS AFTERNOON. HIGH CONFIDENCE FOR AN
EARLY RETURN OF IFR/MVFR CEILINGS THIS EVENING THAT WILL PERSIST
THROUGH MID-MORNING ON WEDNESDAY. ONSHORE WINDS INCREASE ONCE
AGAIN WEDNESDAY AFTERNOON AS SKY CONDITIONS RETURN TO VFR
(MODERATE CONFIDENCE).
SFO BRIDGE APPROACH...SIMILAR TO SFO.
MONTEREY BAY TERMINALS...LIFR CONDITIONS PERSIST AT MRY THIS MORNING
WHILE SNS HAS RETURNED TO VFR. THERE IS MODERATE CONFIDENCE THAT MRY
WILL STAY IFR/MVFR THROUGH MUCH OF THE DAY, BUT DO HAVE THEM
SCATTERING OUT AROUND 20Z. ONSHORE WINDS INCREASE THIS AFTERNOON
BEFORE EASING AFTER SUNSET. HIGH CONFIDENCE FOR AN EARLY RETURN OF
LIFR/IFR CONDITIONS THIS EVENING THAT WILL LIKELY PERSIST THROUGH
WEDNESDAY MORNING. THERE IS THE POTENTIAL FOR FOG EARLY WEDNESDAY
MORNING AT MRY AS WELL.
MARINE
(TODAY THROUGH SUNDAY)
ISSUED AT 235 PM PDT TUE AUG 12 2025
A GENTLE TO MODERATE NORTHWESTERLY BREEZE WILL PREVAIL TONIGHT,
INCREASING TO BECOME FRESH TO STRONG WEDNESDAY WITH WIDESPREAD
STRONG GUSTS BY THURSDAY. MODERATE SEAS WILL BUILD TO BECOME ROUGH
FOR INNER WATERS AND OUTER WATERS BY THURSDAY. NORTHWESTERLY WINDS
WILL INCREASE EVEN MORE SO BY FRIDAY WITH NEAR GALE FORCE GUSTS.
BEACHES
ISSUED AT 248 AM PDT TUE AUG 12 2025
A LONG PERIOD (17 SECONDS) SOUTHWESTERLY SWELL WILL RESULT IN AN
INCREASED RISK FOR SNEAKER WAVES AND RIP CURRENTS THROUGH THIS
EVENING. GREATEST RISK WILL BE ALONG SOUTHWEST FACING BEACHES,
INCLUDING BUT NOT LIMITED TO STINSON BEACH, SANTA CRUZ BOARDWALK
BEACH, AND TWIN LAKES BEACH. SNEAKER WAVES CAN UNEXPECTEDLY RUN
SIGNIFICANTLY FARTHER UP THE BEACH THAN NORMAL, INCLUDING OVER
ROCKS AND JETTIES. REMAIN OUT OF THE WATER TO AVOID HAZARDOUS
SWIMMING CONDITIONS AND NEVER TURN YOUR BACK ON THE OCEAN!
SARMENT
MTR WATCHES/WARNINGS/ADVISORIES
CA...BEACH HAZARDS STATEMENT UNTIL 9 PM PDT THIS EVENING FOR CAZ505-
529.
PZ...SMALL CRAFT ADVISORY UNTIL 9 PM PDT THIS EVENING FOR SF BAY N OF
BAY BRIDGE.
SMALL CRAFT ADVISORY FROM 1 PM TO 9 PM PDT WEDNESDAY FOR SF BAY
N OF BAY BRIDGE.
SMALL CRAFT ADVISORY UNTIL 3 AM PDT THURSDAY FOR PT PINOS TO PT
PIEDRAS BLANCAS 0-10 NM.
SMALL CRAFT ADVISORY FROM 9 PM WEDNESDAY TO 3 AM PDT THURSDAY
FOR PT ARENA TO PT REYES 10-60 NM.
SHORT TERM...MM
LONG TERM....MM
AVIATION...RGASS
MARINE...RGASS
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