554
FXUS66 KMTR 301628
AFDMTR
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SAN FRANCISCO CA
928 AM PDT MON JUN 30 2025
..NEW UPDATE
SYNOPSIS
ISSUED AT 1256 AM PDT MON JUN 30 2025
-TYPICAL MARINE LAYER STRATUS PATTERN THIS WEEK.
-SMALL CHANCE FOR DRY THUNDERSTORMS IN THE NORTH BAY TODAY, AND
AGAIN LATE TUESDAY THROUGH WEDNESDAY MORNING.
-NEAR NORMAL TEMPERATURES WITH A COOLING TREND LATE WEEK.
UPDATE
ISSUED AT 928 AM PDT MON JUN 30 2025
KMUX RADAR PUT INTO PRECIP MODE TO COVER ONGOING HIGH BASED
CONVECTION OCCURRING OVER THE OCEAN WATERS WELL WEST OF SONOMA.
STORMS MOVING IN A EAST TO WEST DIRECTION AWAY FROM LAND AND
CURRENTLY MOSTLY BEYOND OUR 60NM MARINE ZONE 570/571. THIS
CONVECTION WAS NICELY CAPTURED OVER THE LAST 36 HOURS BY MODELS
USING THE MUCAPE AS A TRACER. LOTS OF CONVECTION EXPECTED ACROSS
THE NORTHERN PART OF THE STATE THE NEXT 24-36 HOURS BUT FAIRLY
HIGH CONFIDENCE THAT THE BAY AREA WILL AVOID THUNDERSTORMS THROUGH
AT LEAST TUESDAY AFTERNOON. BEYOND THAT THE 12Z HRRR AND SOME OF
THE HREF MEMBERS STILL SHOW A SMALL PERIOD OF CONCERN TUESDAY
NIGHT INTO THE OVERNIGHT HOURS MAINLY OVER NORTHERN SONOMA AND
NAPA COUNTIES. CHANCES STILL LOOK TO BE LESS THAN 10 PERCENT BUT
CANT COMPLETELY RULE OUT SOME THUNDERSTORMS WITH DRY LIGHTNING
BEING THE BIGGEST CONCERN ESPECIALLY OVER THAT AREA WHERE ERC FUEL
VALUES ARE TRENDING TOWARDS THE 97TH PERCENTILE.
OTHERWISE STILL LOOKING AT A 1000 FOOT MARINE LAYER THAT HAS
ALREADY ALMOST PUSHED BACK TO THE COAST. ANOTHER SEASONABLY WARM
DAY INLAND WITH MILD WEATHER NEAR THE COAST AND BAYS. FORECAST
FOCUS THROUGH WEDS WILL BE ON LOW PROBABILITY BUT HIGH IMPACT
SHOULD ANY CONVECTION OCCUR. BY WEDS THE UPPER LOW MOVES INLAND
AND SOUTHWEST RETURN FLOW REMOVES CONVECTION THREAT.
QUICK GLANCE AT LONG RANGE SUGGESTS A FAIRLY STRONG LATE SEASON
DRY COLD FRONTAL PASSAGE/UPPER TROUGH BY THURSDAY AFTERNOON INTO
4TH OF JULY FRIDAY. THIS WILL KEEP TEMPS BELOW NORMAL WITH BREEZY
ONSHORE WINDS AND DEEP MARINE LAYER. TROUGH TO STAY IN PLACE
THROUGH THE WEEKEND WITH SOME HINTS OF WARMER RIDGE BEYOND JULY
8-9TH.
SHORT TERM
(TODAY AND TONIGHT)
ISSUED AT 1256 AM PDT MON JUN 30 2025
STRATUS HAS PUSHED INLAND A BIT THIS MORNING. THE FT. ORD PROFILER
IS MEASURING THE MARINE LAYER DEPTH AT ROUGHLY 1,200 FEET. NW
WINDS ARE EASING TO A LIGHT BREEZE AS THE BOUNDARY LAYER
DECOUPLES. MIN TEMPS THIS MORNING WILL BE NEAR NORMAL IN THE LOW
TO MID 50S. WHILE THESE SURFACE CONDITIONS ARE ALL FAIRLY TYPICAL
FOR SUMMER, THE PATTERN IS A BIT MORE INTERESTING THAN NORMAL. A
500 MB CUT-OFF LOW JUST OFFSHORE THE SAN FRANCISCO BAY AREA IS
BRINGING S TO SE WINDS TO THE MIDDLE TROPOSPHERE, SURROUNDED BY NW
WINDS AT THE SURFACE AND SW WINDS IN THE JET STREAM. THIS COMPLEX
WIND PROFILE HAS THE POTENTIAL TO BRING ELEVATED MOISTURE FROM THE
SUBTROPICS, WITH MODEL GUIDANCE SUGGESTING THE PWAT WILL EXCEED
1" IN THE NORTH BAY (ROUGHLY 150%-200% OF NORMAL). THERE IS A
GREAT DEAL OF VARIANCE REGARDING THE AMOUNT, TIMING, AND LOCATION
OF THIS MOISTURE PLUME. THERE IS MORE AGREEMENT THAT THE MOISTURE
WILL BE ELEVATED, WITH DRIER AIR BETWEEN THE TOP OF THE MARINE
LAYER AND 850 MB. THIS SET-UP OF UNSTABLE HUMID AIR ABOVE DRY AIR
HAS THE POTENTIAL TO PRODUCE DRY THUNDERSTORMS, WHERE THE RAIN
EVAPORATES BEFORE IT REACHES THE SURFACE. IN THESE STORMS, ANY
CLOUD-TO-GROUND LIGHTNING HAS A MUCH BETTER CHANCE TO IGNITE
WILDFIRES SINCE THERE IS LITTLE TO NO RAIN TO INHIBIT IGNITION.
THE BEST CHANCE FOR THESE STORMS IS OUTSIDE OF OUR AREA IN THE
HIGHER TERRAIN OF THE SIERRA AND CASCADES IN NORTHERN CALIFORNIA.
FORTUNATELY THE CHANCES OF THESE STORMS DEVELOPING REMAINS LESS
THAN 10% IN THE NORTH BAY, WITH THE PROBABILITY DECREASING FURTHER
SOUTH.
LONG TERM
(TUESDAY THROUGH SUNDAY)
ISSUED AT 1256 AM PDT MON JUN 30 2025
THE UPPER LEVEL LOW WILL GRADUALLY SHIFT SOUTH, REACHING SOUTHERN
CALIFORNIA BY WEDNESDAY. ANOTHER PULSE OF MOISTURE WILL PUSH
THROUGH LATE TUESDAY OR EARLY WEDNESDAY MORNING, THIS TIME COMING
FROM THE NORTH AHEAD OF A COLD FRONT. MID-LEVEL LAPSE RATES
INCREASE TO AROUND 8 C/KM, REINVIGORATING THE CHANCES FOR
THUNDERSTORMS. THE NBM IS KEEPING THE CHANCES LESS THAN 10%, BUT
THE NAM BRINGS MUCAPE NEAR 900 J/KG AT SANTA ROSA WEDNESDAY
MORNING. THAT'S JUST ONE DETERMINISTIC MODEL, AND REMAINS AN
OUTLIER, BUT IT WILL BE INTERESTING TO SEE WHAT THE OTHER HIGH
RESOLUTION MODELS COME UP WITH AS THEY START TO RESOLVE
WEDNESDAY'S PATTERN. WITH MUCH DRIER AIR AROUND 900 MB, THERE WILL
BE SOME CONVECTIVE INHIBITION TO OVERCOME AS WELL. BESIDES THE
CONVECTIVE CHANCES, THE SLOW MOVING LOW WILL LIKELY DEEPEN THE
MARINE LAYER A BIT ACROSS THE CENTRAL COAST. THE 850 MB
TEMPERATURE WILL REMAIN WELL ABOVE NORMAL UNTIL A COLD FRONT
MOVES THROUGH LATE WEDNESDAY OR EARLY THURSDAY. THIS WILL BE
FOLLOWED BY A COOLING TREND INLAND, WITH STRONGER ONSHORE WINDS IN
THE AFTERNOON. IN ADDITION TO STRONGER WINDS, A DRIER AIR MASS
WILL ALSO FOLLOW THE COLD FRONT, MARGINALLY INCREASING FIRE
WEATHER CONDITIONS. FORTUNATELY THE ONSHORE WINDS WILL RETAIN
SOME MOISTURE, AND THE TEMPS WILL BE BELOW NORMAL, KEEPING THE
CONDITIONS MORE MODERATE AND LOCALIZED. A SECOND TROUGH WILL MOVE
THROUGH FRIDAY, EXTENDING THE COOLER THAN AVERAGE TEMPERATURES
INTO THE HOLIDAY WEEKEND.
AVIATION
(12Z TAFS)
ISSUED AT 524 AM PDT MON JUN 30 2025
IFR AND LIFR CIGS REMAIN IN PLACE ALONG THE COAST AND HAVE FILTERED
INTO THE NORTH BAY VALLEYS AND ARE AFFECTING OAK. MOMENTS OF LOW
CLOUDS ALSO LOOK TO AFFECT SJC LATER INTO THE MORNING. INLAND
CLEARING BEGINS IN THE MID MORNING WITH MOST TAF SITES GOING VFR
BEFORE THE MIDDAY. THE EXCEPTION WILL BE HAF THAT KEEPS CIGS THROUGH
THE TAF PERIOD. WINDS LOOK TO STAY LIGHT THROUGH THE MORNING AND
INCREASE INTO THE AFTERNOON, BUT MOSTLY JUST TO MODERATE SPEEDS.
EXPECT WINDS TOR REDUCE INTO THE EVENING AS CIGS BEGIN TO MOVE BACK
INLAND, AFFECTING THE MONTEREY BAY TERMINALS AS WELL AS OAK INTO THE
EARLY NIGHT. THE NORTH BAY WILL SEE CIGS RETURN IN THE LATE NIGHT.
CIGS LOOK TO BEGIN TO ERODE AGAIN INTO MID TO LATE TUESDAY.
VICINITY OF SFO...VFR THROUGH THE TAF PERIOD. WINDS REDUCE INTO THE
MID MORNING, BECOMING LIGHT BEFORE MORE MODERATE WEST WINDS ARRIVE
INTO THE AFTERNOON. EXPECT THESE WINDS TO LAST INTO THE EARLY NIGHT
BEFORE BECOMING LIGHT ONCE AGAIN.
SFO BRIDGE APPROACH...SIMILAR TO SFO.
MONTEREY BAY TERMINALS...LIFR CIGS LINGER INTO THE LATE MORNING WITH
SOME POCKETS OF MIST AND DRIZZLE IN THE AREA. WINDS BECOME MODERATE
AS CIGS ERODE OVER THE TERMINALS, BUT EXPECT CLOUD COVER TO LINGER
OVER THE MONTEREY BAY ITSELF. AS WINDS REDUCE IN THE EVENING AND
INTO THE NIGHT, IFR CIGS MOVE INLAND AFFECTING THE TERMINALS.
MARINE
(TODAY THROUGH SATURDAY)
ISSUED AT 524 AM PDT MON JUN 30 2025
WINDS AND SEAS CONTINUE TO EASE THROUGH MONDAY. EXPECT
SIGNIFICANT WAVE HEIGHTS TO BUILD AGAIN ON TUESDAY WITH INCREASING
NORTHWEST BREEZES AFFECTING THE NORTHERN OUTER WATERS. THESE
ELEVATED SEAS AND WINDS WILL SPREAD ACROSS THE WATERS INTO THE MID
WEEK AND LOOK TO LAST INTO THE NEXT WORK WEEK.
MTR WATCHES/WARNINGS/ADVISORIES
CA...NONE.
PZ...SMALL CRAFT ADVISORY FROM 3 PM TUESDAY TO 3 AM PDT WEDNESDAY FOR
PT ARENA TO PT REYES 10-60 NM.
UPDATE.......RWW
SHORT TERM...FLYNN
LONG TERM....FLYNN
AVIATION...MURDOCK
MARINE...MURDOCK
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