030
FXUS66 KMTR 120844
AFDMTR
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SAN FRANCISCO CA
144 AM PDT WED MAR 12 2025
..NEW SYNOPSIS, SHORT TERM, LONG TERM
SYNOPSIS
ISSUED AT 1212 AM PDT WED MAR 12 2025
AN ACTIVE WEATHER PATTERN ARRIVES TODAY WITH PERIODS OF RAIN,
STRONG WIND, THUNDERSTORM CHANCES, AND SOME SNOW TO THE HIGHER
REGIONAL MOUNTAINS. WHILE THE BULK OF THE IMPACTS ARRIVE TODAY
THROUGH THURSDAY, DISTURBED WEATHER WILL CONTINUE INTO EARLY NEXT
WEEK.
SHORT TERM
(TODAY AND TONIGHT)
ISSUED AT 1212 AM PDT WED MAR 12 2025
PREFRONTAL RAIN OVER THE COASTAL WATERS IS JUST NOW GETTING INTO
RADAR RANGE. THIS FIRST ROUND WILL ARRIVE IN THE NORTH BAY BAY
AROUND MID TO LATE MORNING AND CONTINUE SLIDING SOUTH THROUGH THE
AFTERNOON. STRONG SOUTHERLY WINDS IN THE WARM SECTOR WILL
COINCIDE WITH THE MAIN RAIN BAND TODAY, MAKING FOR NASTY
CONDITIONS OUTSIDE. THE WIND HAS TRENDED STRONGER ON THE LATEST
HIGH RESOLUTION GUIDANCE. THE OFFICIAL FORECAST LEANS HEAVILY ON
THE 12/00Z LOCAL WRF, AND BRINGS A SEVERAL HOURS OF 30-55 MPH
GUSTS TO THE ENTIRE BAY AREA AND CENTRAL COAST. AS SUCH, WE'VE
ISSUED A WIND ADVISORY FROM 8 AM THROUGH 8 PM TODAY. THE RAIN
FORECAST HAS CHANGED SLIGHTLY WITH A LATER ARRIVAL, BUT OVERALL
SIMILAR ACCUMULATION AS THE PREVIOUS FEW FORECASTS. COASTAL AREAS
WILL SEE 1-1.5", WITH 2-4" IN THE COASTAL MOUNTAINS. INLAND
VALLEYS WILL SEE ANYWHERE FROM 0.5-1", WITH 1-2" IN THE INLAND
MOUNTAINS. AFTER THE COLD FRONT PUSHES THROUGH THIS
AFTERNOON/EVENING, COLD AIR ALOFT WILL SETTLE IN, CREATING AN
UNSTABLE ATMOSPHERE. THIS WILL CHANGE THE PRECIPITATION MODE FROM
STEADY STRATIFORM RAIN TO CONVECTIVE SHOWERS. MOST OF THE
PRECIPITATION WILL FALL AS RAIN TODAY, WITH HIGHER ELEVATIONS
SWITCHING TO SNOW OVERNIGHT AFTER THE COLD AIR STARTS TO SETTLE IN
BEHIND THE FRONT. THERE IS GOOD AGREEMENT THAT THE 500 MB HEIGHT
WILL DROP TO AROUND 536-538 DM BY THURSDAY MORNING. WHILE THAT'S
ENOUGH TO BRING SOME HIGH ELEVATION SNOW, IT'S NOT QUITE GETTING
COLD ENOUGH FOR ANYTHING EXTREME. FOR REFERENCE, THE LAST TIME
HIGHWAY 17 WAS SHUT DOWN DUE TO SNOW (2/24/23), THE 500 MB HEIGHT
WAS 533 DM. THE LAST TIME IT SNOWED IN SAN FRANCISCO (2/5/76), THE
500 MB HEIGHT WAS 528 DM. THE BIGGEST CONCERN FOR IMPACTS TODAY
IS THE COMBINATION OF WIND AND RAIN, WHICH COULD LEAD TO SOME
DOWNED TREES AND RELATED IMPACTS TO ROADWAYS AND POWER GRIDS. WE
ARE NOT EXPECTING THE LARGE RIVERS TO FLOOD, BUT URBAN AND SMALL
STREAM FLOODING, AS WELL AS SHALLOW LANDSLIDES, ARE POSSIBLE AS
THE NARROW BAND OF HIGH INTENSITY RAIN PUSHES THROUGH TODAY.
LONG TERM
(THURSDAY THROUGH TUESDAY)
ISSUED AT 1212 AM PDT WED MAR 12 2025
THURSDAY LOOKS LIKE THE BEST DAY FOR THUNDERSTORM CHANCES, BUT
IT'S NOT A SLAM DUNK. AS THE COLD AIR CONTINUES TO RUSH IN
THROUGH THE MORNING, SUN BREAKS WILL ALLOW THE SURFACE TO WARM
MODERATELY. THIS COMBINATION OF COLD OVER WARM IS UNSTABLE. THE
WARM AIR NEAR THE SURFACE WILL RISE, EXPAND AND COOL TO THE DEW
POINT, AND CONDENSE OUT CLOUD DROPLETS. WITH RELATIVELY LOW
HUMIDITY AT THE SURFACE THURSDAY, THE CLOUD BASES WILL BE HIGHER
THAN NORMAL, AND THIS CLOUD FORMATION PROCESS WILL HAPPEN MOSTLY
ABOVE THE FREEZING LEVEL. THAT'S IMPORTANT BECAUSE IT MEANS THE
CLOUDS WILL CONTAIN A SIGNIFICANT AMOUNT OF ICE. ICE OBVIOUSLY CAN
MEAN HAIL, BUT IT'S ALSO A NECESSARY INGREDIENT FOR THUNDERSTORM
DEVELOPMENT. IT'S THE STATIC BUILDUP BETWEEN COLLIDING ICE
PARTICLES THAT BUILDS THE ELECTRICAL CHARGE NECESSARY FOR
LIGHTNING STRIKES. THE COLD AIR ALOFT AND STEEP LAPSE RATES (AS
HIGH AS 9 C/KM IN THE AFTERNOON) ARE FAVORABLE, BUT THE MOISTURE
CONTENT IS RELATIVELY LOW AND DECREASING IN THE POST-FRONTAL
ENVIRONMENT (PW AROUND 0.35"). THIS COULD BE THE LIMITING FACTOR
FOR THUNDERSTORM DEVELOPMENT AND MAY SKEW ANY ACTIVITY EARLIER IN
THE DAY WHEN THE HUMIDITY IS STILL ELEVATED FROM WEDNESDAY'S RAIN.
THERE LOOKS TO BE A BRIEF LULL IN SHOWERS AS THE DRY AIR FILTERS
IN LATE THURSDAY. IT WON'T LAST LONG, HOWEVER, AS THE NEXT SYSTEM
COMES ROLLING IN FROM THE EASTERN PACIFIC FRIDAY MORNING. THIS
WILL BRING ANOTHER ROUND OF STRATIFORM RAIN, BUT THE IMPACTS LOOK
LESS THAN THE FIRST SYSTEM. THE THIRD, AND WEAKEST, SYSTEM WILL
BRING ANOTHER ROUND OF RAIN MONDAY. THE REST OF THE WEEK IS MORE
COMPLICATED, WITH A LOT OF UNCERTAINTY BEYOND NEXT MID WEEK BUT
THE PATTERN WILL LIKELY REMAIN ACTIVE.
AVIATION
(06Z TAFS)
ISSUED AT 937 PM PDT TUE MAR 11 2025
LOW CLOUDS /VFR-MVFR/ ARE INCREASING ACROSS THE FORECAST AREA.
WINDS WILL SHIFT OVER TO A SOUTH TO SOUTHEAST DIRECTION TONIGHT
AND STRENGTHEN AND BECOME GUSTY AHEAD OF A STRONG COLD FRONT
ARRIVING WEDNESDAY. CONDITIONS AT THE TERMINALS WEDNESDAY MORNING
AND AFTERNOON WILL DETERIORATE TO MVFR-IFR IN RAIN, HEAVY AT
TIMES, INCLUDING STRONG AND GUSTY WINDS UP THROUGH COLD FRONTAL
PASSAGE. COLD, SHOWERY WEATHER WILL CONTINUE IN THE POST FRONTAL
ENVIRONMENT WEDNESDAY NIGHT. MIXING WINDS FROM THE SURFACE UP
THROUGH THE LOWER LEVELS SHOULD HELP TO PRECLUDE THE NEED FOR
INDICATING LOW LEVEL WIND SHEAR (LLWS) IN THE TAFS FOR NOW, BUT
WILL CONTINUE TO MONITOR THE LATEST OBSERVATIONS, FORECASTS, PILOT
REPORTS, ETC. AND ADJUST THE TAFS AS NEEDED.
VICINITY OF SFO...MVFR WITH THE SURFACE WIND SHIFTING TO SOUTH-
SOUTHEAST 5 TO 10 KNOTS TONIGHT, THEN A SOUTHEAST WIND INCREASES
TO 25-30 WITH GUSTS TO THE 35-40 KNOTS RANGE WEDNESDAY MORNING
AHEAD OF THE INCOMING COLD FRONT. RAIN, HEAVY AT TIMES, INCLUDING
STRONG AND GUSTY SOUTH-SOUTHEAST WIND DEVELOPING DURING THE MORNING
WITH COLD FRONTAL WIND SHIFT FORECAST 21Z WEDNESDAY. GUSTY WEST WIND
TO 25 KNOTS CONTINUING WEDNESDAY NIGHT.
SFO BRIDGE APPROACH...SIMILAR TO SFO.
MONTEREY BAY TERMINALS...MVFR TONIGHT AND WEDNESDAY EXCEPT
CONDITIONS DETERIORATING TO AREAS IFR WITH THE APPROACHING STRONG
COLD FRONT WEDNESDAY LATE MORNING AND AFTERNOON. RAIN BECOMING
HEAVY AT TIMES WEDNESDAY WITH STRONG AND GUSTY SOUTH TO SOUTHEAST
WINDS UP THROUGH COLD FRONTAL PASSAGE DURING THE AFTERNOON. COLD
FRONTAL PASSAGE WEDNESDAY CURRENTLY FORECAST 22Z KMRY AND 23Z
KSNS. SHOWERS AND GUSTY POST FRONTAL WINDS CONTINUE WEDNESDAY
NIGHT.
MARINE
(TONIGHT THROUGH NEXT MONDAY)
ISSUED AT 924 PM PDT TUE MAR 11 2025
LIGHT TO MODERATE SEAS AND WINDS LAST INTO THE LATE NIGHT.
SOUTHERLY WINDS WILL INCREASE TONIGHT AND WEDNESDAY AS A STRONG
COLD FRONT APPROACHES FROM THE NORTHWEST WITH GALE FORCE GUSTS
EXPECTED AS IT PASSES. SCATTERED THUNDERSTORMS WILL DEVELOP
WEDNESDAY AFTERNOON INTO THURSDAY WHICH PRESENTS A RISK FOR
LOCALLY HEAVY RAINFALL AND GUSTY WINDS, LIGHTNING, AND PEA SIZED
HAIL. SEAS WILL BE ROUGH TO VERY ROUGH WEDNESDAY THROUGH THE
WEEKEND.
BEACHES
ISSUED AT 420 AM PDT TUE MAR 11 2025
HAZARDOUS BEACH CONDITIONS ARE EXPECTED WEDNESDAY AND THURSDAY
AS MODERATE PERIOD WESTERLY SWELL BUILDS TO SUPPORT BREAKING
WAVES UP TO 15 FEET. AS ALWAYS, PLEASE REMEMBER TO STAY OFF OF
ROCKS AND JETTIES, KEEP PETS ON A LEASH, AND NEVER TURN YOUR BACK
ON THE OCEAN!
SARMENT
MTR WATCHES/WARNINGS/ADVISORIES
CA...WIND ADVISORY FROM 8 AM THIS MORNING TO 8 PM PDT THIS EVENING
FOR CAZ006-502>506-508>510-512>518-528>530.
PZ...SMALL CRAFT ADVISORY UNTIL 9 AM PDT THIS MORNING FOR MRY BAY-
PIGEON PT TO PT PINOS 0-10 NM-PIGEON PT TO PT PINOS 10-60
NM-PT PINOS TO PT PIEDRAS BLANCAS 0-10 NM-PT REYES TO
PIGEON PT 0-10 NM-SF BAY N OF BAY BRIDGE.
GALE WARNING FROM 9 AM THIS MORNING TO 3 PM PDT THIS AFTERNOON
FOR SF BAY N OF BAY BRIDGE.
GALE WARNING FROM 9 AM THIS MORNING TO 9 PM PDT THIS EVENING FOR
MRY BAY-PIGEON PT TO PT PINOS 0-10 NM-PIGEON PT TO PT PINOS
10-60 NM-PT PINOS TO PT PIEDRAS BLANCAS 0-10 NM-PT REYES TO
PIGEON PT 0-10 NM.
GALE WARNING UNTIL 9 PM PDT THIS EVENING FOR PT ARENA TO PT
REYES 0-10 NM-PT ARENA TO PT REYES 10-60 NM.
SMALL CRAFT ADVISORY UNTIL 3 AM PDT EARLY THIS MORNING FOR PT
ARENA TO PT REYES 10-60 NM.
SHORT TERM...FLYNN
LONG TERM....FLYNN
AVIATION...CANEPA
MARINE...CANEPA
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