259
FXUS66 KMTR 130443
AFDMTR
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SAN FRANCISCO CA
943 PM PDT TUE AUG 12 2025
..NEW AVIATION
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.
UPDATE
ISSUED AT 900 PM PDT TUE AUG 12 2025
SATELLITE IMAGERY SHOWS STRATUS EXTENDING INTO THE SONOMA COUNTY
VALLEYS, THE BAY AREA, THE MONTEREY BAY REGION, AND THE NORTHERN
SALINAS VALLEY. THE MOISTURE STEMMING FROM THE REMNANTS OF IVO IS
MOVING NORTHWARD, WITH MOST OF THE MOISTURE PLUME REMAINING OFF
THE COAST OF THE BAY AREA. SOME OF THE ASSOCIATED HIGH CLOUDS ARE
INTRUDING INTO THE BAY AREA, BUT DESPITE SOME VERY LIGHT RADAR
RETURNS, NO ACCUMULATING RAINFALL HAS BEEN RECORDED ANYWHERE
WITHIN THE REGION. NO CHANGES TO THE FORECAST. THE BEACH HAZARDS
STATEMENT HAS BEEN ALLOWED TO EXPIRE, BASED ON THE DECAY OF THE
SOUTHWESTERLY SWELL.
DIALH
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 BUSY 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 EVEN 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
(06Z TAFS)
ISSUED AT 942 PM PDT TUE AUG 12 2025
NORTH BAY TERMINALS ARE CURRENTLY VFR BUT SATELLITE TRENDS INDICATE
THAT LOW STRATUS WILL CONTINUE TO FILL IN THE VALLEYS NEAR KSTS AND
KAPC OVER THE NEXT COUPLE OF HOURS. BAY AREA TERMINALS ARE EXPECTED
TO HOVER BETWEEN MVFR/IFR THROUGH THE OVERNIGHT INTO LATE WEDNESDAY
MORNING. SIMILAR FORECAST FOR THE MONTEREY TERMINALS WHERE THE
WINDOW FOR VFR WEDNESDAY AFTERNOON IS EXPECTED TO BE SHORTER.
VICINITY OF SFO...BREEZY ONSHORE WINDS HAVE EASED LATE THIS EVENING
BUT ARE EXPECTED TO INCREASE AGAIN WEDNESDAY AFTERNOON THROUGH
SUNSET. MVFR/IFR CEILINGS ARE PROGGED TO PERSIST THROUGH THE
OVENIGHT AND SCATTER OUT AT SIMILAR TIMES AS THE PREVIOUS FEW DAYS,
BY MID/LATE MORNING WEDNESDAY WITH SIMILAR RETURN TIMES IN THE
EVENING.
SFO BRIDGE APPROACH...SIMILAR TO SFO.
MONTEREY BAY TERMINALS...CURRENT IFR CONDITIONS ARE EXPECTED TO DROP
TO LIFR DURING THE OVERNIGHT HOURS, LIFTING BACK UP TO IFR AFTER
SUNRISE. SOME CLEARING IS EXPECTED BY LATE MORNING/EARLY AFTERNOON,
ESPECIALLY AT KSNS, BUT KMRY WILL SEE SOME LINGERING LOW STRATUS
NEAR THE COASTLINE MOST OF THE DAY EVEN WHEN VFR CONDITIONS RETURN
WEDNESDAY AFTERNOON. EXPECT SIMILAR RETURN TIMES FOR MVFR/IFR
CEILINGS LATE IN THE AFTERNOON/EARLY EVENING.
MARINE
(TONIGHT THROUGH NEXT MONDAY)
ISSUED AT 856 PM PDT TUE AUG 12 2025
MODERATE NORTHWESTERLY BREEZES WILL PERSIST TONIGHT, BECOMING
FRESH TO STRONG WEDNESDAY, WITH INCREASING STRONG GUSTS ON
THURSDAY. MODERATE SEAS WILL RESPOND TO THE STRONG GUSTS BECOMING
ROUGH ON THURSDAY. NORTHWESTERLY WINDS WILL INCREASE FURTHER ON
FRIDAY, APPROACHING GALE FORCE SPEEDS IN THE OUTER WATERS.
MTR WATCHES/WARNINGS/ADVISORIES
CA...NONE.
PZ...SMALL CRAFT ADVISORY FROM 1 PM TO 9 PM PDT WEDNESDAY FOR SF BAY
N OF BAY BRIDGE.
SMALL CRAFT ADVISORY FROM 3 PM THURSDAY TO 3 AM PDT FRIDAY FOR
PT ARENA TO PT REYES 0-10 NM-PT PINOS TO PT PIEDRAS BLANCAS
0-10 NM.
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 FRIDAY FOR
PT ARENA TO PT REYES 10-60 NM.
SHORT TERM...MM
LONG TERM....MM
AVIATION...JM
MARINE...JM
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