290
FXUS66 KMTR 180451
AFDMTR
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SAN FRANCISCO CA
951 PM PDT SUN AUG 17 2025
..NEW AVIATION
KEY MESSAGES
UPDATED AT 159 PM PDT SUN AUG 17 2025
- PATCHY FOG AND/OR DRIZZLE ALONG THE COAST SUNDAY MORNING
- WARMING TREND THIS WEEK
UPDATE
ISSUED AT 854 PM PDT SUN AUG 17 2025
IF YOU'RE LOCATED IN THE INTERIOR BAY AREA AND LOOK OUT YOUR WINDOW
RIGHT NOW, THERE IS A HIGH LIKELIHOOD YOU'LL SEE CLEAR SKIES! THIS
IS QUITE DIFFERENT FROM WHAT WE SAW AT THIS TIME YESTERDAY
(WIDESPREAD OVERCAST CONDITIONS). A DRIER AIR MASS HAS ARRIVED IN
THE WAKE OF YESTERDAY'S WEAK FRONTAL PASSAGE WITH THE 00Z SOUNDING
SHOWING ONLY 0.52 INCHES OF PRECIPITABLE WATER (COMPARE THIS TO
YESTERDAY'S 00Z SOUNDING WHICH SAW A PWAT VALUE OF 1.47 IN). THIS
HAS CONTRIBUTED TO BOTH OUR CLEARER EVENING SKIES AND IS LOWERING
OUR CHANCES FOR DRIZZLE TONIGHT. ANOTHER SIDE EFFECT OF CLEAR SKIES
ACROSS THE INTERIOR IS THAT TEMPERATURES ARE COOLING MUCH FASTER
TONIGHT THAN THEY WERE LAST NIGHT. MOST SITES ARE RUNNING AROUND 1
TO 5 DEGREES COOLER TONIGHT THAN LAST NIGHT BUT A NUMBER OF SITES
ACROSS THE NORTH BAY ARE RUNNING BETWEEN 10 TO 15 DEGREES COOLER
TONIGHT. STRATUS IS EXPECTED TO RETURN ALONG THE COAST AND BAY
SHORELINE TONIGHT BUT ANY FOG OR PATCHY DRIZZLE CONCERNS WILL BE
KEPT ALONG THE COASTLINE. NO CHANGES TO THE OVERALL FORECAST
NEEDED.
SHORT TERM
ISSUED AT 159 PM PDT SUN AUG 17 2025 (THIS EVENING THROUGH
MONDAY)
AFTERNOON SATELLITE SHOWS SOME REMNANTS OF A WEAK SURFACE COLD
FRONT DRAPED ACROSS THE THE COASTAL REACHES OF THE BAY AREA. THIS
HAS KEPT CLOUDS ALONG COASTAL AREAS OF NORTH BAY DOWN TO HALF MOON
BAY. BY ALL ACCOUNTS, THIS FRONT HAS STALLED. THIS STALLED
BOUNDARY WILL PROVIDE A FOCUS FOR SOME DRIZZLE TO POTENTIALLY
DEVELOP. CONFIDENCE WAS NOT HIGH ENOUGH TO PAINT IT INTO THE
FORECAST, SO LEFT IT WITH PATCHY FOG FOR NOW. THIS MAY NEED TO BE
UPDATED IF CONDITIONS CHANGE, NAMELY THE FRONTAL BOUNDARY TRIES TO
HANG ON LONGER THAN EXPECTED. THE HIGHER PROBABILITY IS THAT THE
BOUNDARY FADES INTO OBSCURITY, ALLOWING FOR UPPER LEVEL RIDGING TO
START TO FLEX AGAIN. OVERALL, TONIGHT THROUGH MONDAY WILL SEE
RELATIVELY NON-IMPACTFUL WEATHER.
SHORT TERM
ISSUED AT 159 PM PDT SUN AUG 17 2025 (THIS EVENING THROUGH
MONDAY)
AFTERNOON SATELLITE SHOWS SOME REMNANTS OF A WEAK SURFACE COLD
FRONT DRAPED ACROSS THE THE COASTAL REACHES OF THE BAY AREA. THIS
HAS KEPT CLOUDS ALONG COASTAL AREAS OF NORTH BAY DOWN TO HALF MOON
BAY. BY ALL ACCOUNTS, THIS FRONT HAS STALLED. THIS STALLED
BOUNDARY WILL PROVIDE A FOCUS FOR SOME DRIZZLE TO POTENTIALLY
DEVELOP. CONFIDENCE WAS NOT HIGH ENOUGH TO PAINT IT INTO THE
FORECAST, SO LEFT IT WITH PATCHY FOG FOR NOW. THIS MAY NEED TO BE
UPDATED IF CONDITIONS CHANGE, NAMELY THE FRONTAL BOUNDARY TRIES TO
HANG ON LONGER THAN EXPECTED. THE HIGHER PROBABILITY IS THAT THE
BOUNDARY FADES INTO OBSCURITY, ALLOWING FOR UPPER LEVEL RIDGING TO
START TO FLEX AGAIN. OVERALL, TONIGHT THROUGH MONDAY WILL SEE
RELATIVELY NON-IMPACTFUL WEATHER.
LONG TERM
ISSUED AT 159 PM PDT SUN AUG 17 2025 (MONDAY NIGHT THROUGH NEXT
SATURDAY)
NOW TO THE IMPACTFUL PORTIONS OF THE FORECAST. HEAT. HIGH PRESSURE
OVER THE 4 CORNERS REGION OF THE DESERT SOUTHWEST WILL START TO
NOSE INTO OUR SERVICE AREA ON MONDAY, GRADUALLY STRENGTHENING
THROUGH THE WEEK. THE CHALLENGE WITH THE FORECAST IS WHAT THE AREA
OF LOW PRESSURE OVER THE GULF OF ALASKA WILL DO. SO FAR THIS
SUMMER IT HAS BEEN SENDING TROUGHS ACROSS OUR AREA, KEEPING US ON
THE MODERATE SIDE WITH ONSHORE WINDS AND AMPLE MOISTURE. THIS
TREND LOOKS TO CONTINUE FOR THE START OF THE WEEK. HOWEVER,
ENSEMBLE MODELS ARE INDICATING A STRENGTHENING OF THE 4 CORNERS
HIGH TO THE POINT THAT THERE IS INCREASING PROBABILITY THE HIGH
PRESSURE FORCES THE LOW PRESSURE OUT TO SEA. THE WAY TO WATCH THIS
OVER THE WEEK WILL BE IN THE TEMPERATURES OVER THE SOUTHERN HALF
OF THE STATE AND EVEN SOUTHER NV. AS THOSE HEAT UP, WE'LL BE
SEEING THE RIDGE BUILD TOWARDS US. IT'LL FIRST CONSUME INTERIOR
MONTEREY COUNTY AND SAN BENITO COUNTY, THEN CREEP INTO INTERIOR
EAST BAY AND MARCH INTO INTERIOR NORTH BAY. WE SHOULD SEE THE APEX
OF THE HEAT THURSDAY AND FRIDAY. THE TWO CHALLENGES TO THE
FORECAST WILL MAGNITUDE OF THE HEAT AND WESTWARD EXTENT OF THE
HEAT. RIGHT NOW THE NBM HAS LESS THAN A 3 DEGREE SPREAD IN
PROBABILITIES OVER THE MOST IMPACTED AREAS. THAT SAID, THE ENTIRE
SPREAD COULD BE ON THE LOW SIDE, MEANING THE NBM IS UNDERDOING THE
MAGNITUDE. AT THIS POINT I WOULD GIVE THE FORECAST A 70% CHANCE OF
BEING UNDERDONE. AS WE GET MORE DATA AND SEE HOW THIS IS EVOLVING,
EXPECT THE HIGH TEMPERATURE FORECAST FOR THURS AND FRI TO INCREASE
BY A FEW DEGREES. TAKING MORE AREAS INTO THE UPPER 90S AND LOW
100S. THIS PLAYS DIRECTLY INTO THE SECOND CHALLENGE, THE WESTWARD
REACH OF THE RIDGE. MODELS ARE NOT IN GOOD AGREEMENT WITH HOW FAR
WEST THE RIDGE CAN NOSE AND ENSEMBLE MEANS ARE SIMPLY WASHING IT
OUT. IF THE PATTERNS OF THIS SUMMER HOLD TRUE, THE COAST WILL
REAMIN THE SANCTUARY FROM THE INTERIOR HEAT. HOWEVER, WE ARE REACH
THE CLIMATOLOGICAL TIME OF THE YEAR WE START TO SEE HEAT REACH THE
COAST. WHILE IT IS NOT A TRUE NATURE VS NURTURE ARGUMENT,
CLIMATE, OR "NATURE" IN THIS ANALOGY, DOES PLAY A ROLE AND MAY END
UP BEING THE ARBITER OF COASTAL HEAT. THE OCEAN PREDICTION
CENTER'S 96 HOUR FORECAST CHART SHOWS A THERMAL (OR INVERTED)
TROUGH THURSDAY MORNING JUST OFF THE COAST OF THE BAY AREA. THIS
SCREAMS HEAT MOVING CLOSER TO THE COAST. ALL THAT SAID, BE READY
FOR HEAT WHEREVER YOU ARE LOCATED. FROM SANTA CRUZ AND SAN
FRANCISCO TO BRENTWOOD AND PINNACLES, IT WILL GET HOT. HEATRISK
AT THIS TIME IS MOSTLY MODERATE FOR THURS AND FRI, BUT DON'T BE
SURPRISED TO SEE IT GO MAJOR WITH AREAS OF EXTREME. WE WILL BE
WATCHING THIS CLOSELY FOR ANY ISSUANCE OF HEAT PRODUCTS. EITHER
WAY IT WILL BE A JARRING SHIFT FROM BEING BELOW NORMAL FOR MONTHS
TO BEING 5 TO 15 DEGREES ABOVE NORMAL. PREPARE NOW FOR A SHARP
WARM UP.
AVIATION
(06Z TAFS)
ISSUED AT 950 PM PDT SUN AUG 17 2025
STRATUS LINGERS ALONG THE IMMEDIATE COAST FROM POINT REYES THROUGH
HAF AND IN AREAS OF THE INTERIOR EAST BAY, WITH CLEAR CONDITIONS
EVERYWHERE ELSE. SOME FURTHER DEVELOPMENT IS POSSIBLE WITH MODERATE
CONFIDENCE IN STRATUS IMPACTS EARLY MONDAY MORNING IN THE NORTH BAY
VALLEYS AND MONTEREY BAY. BREEZY ONSHORE WINDS CONTINUE TO DIMINISH
THROUGH THE EVENING WITH LIGHT AND VARIABLE WINDS OVERNIGHT. STRATUS
RETREATS TO THE IMMEDIATE COAST ON MONDAY MORNING WITH BREEZY
ONSHORE FLOW RESUMING IN THE AFTERNOON.
VICINITY OF SFO... MVFR CEILINGS WILL SOON DEVELOP AND PERSIST
OVERNIGHT, BEFORE MIXING OUT MONDAY MORNING WITH BREEZY WEST FLOW
RESUMING IN THE AFTERNOON. STRATUS IS EXPECTED TO RETURN SOMETIME
MONDAY NIGHT OR EARLY TUESDAY MORNING, WITH MODERATE CONFIDENCE ON
STRATUS TIMING. A POSSIBLE COMPLICATING FACTOR, AS HINTED BY HIGH
RESOLUTION MODEL DATA, IS THE POSSIBILITY FOR THE EDGE OF THE
STRATUS DECK MONDAY NIGHT TO SET UP OVER THE TERMINAL AREA.
SFO BRIDGE APPROACH... SIMILAR TO SFO.
MONTEREY BAY TERMINALS... VFR CONDITIONS CONTINUE FOR AT LEAST THE
NEXT SEVERAL HOURS. MONTEREY BAY HAS REMAINED MAINLY CLEAR THROUGH
THE EVENING SO FAR, WITH UPDATED MODEL GUIDANCE CASTING DOUBT ON ANY
STRATUS IMPACTING THE TERMINALS. THUS, THE PREVAILING CEILING AT MRY
OVERNIGHT HAS BEEN CONVERTED TO A TEMPO GROUP AND THE EXISTING
STRATUS TEMPO AT SNS HAS BEEN REMOVED. WILL MONITOR FOR POTENTIAL
RADIATIONAL STRATUS DEVELOPMENT OVERNIGHT. ANY STRATUS THAT DOES
FORM MIXES OUT THROUGH MONDAY MORNING. LIGHT AND VARIABLE WINDS
CONTINUE OVERNIGHT BEFORE BREEZY NORTHWEST FLOW RESUMES MONDAY
AFTERNOON.
MARINE
(TONIGHT THROUGH NEXT SATURDAY)
ISSUED AT 854 PM PDT SUN AUG 17 2025
NORTHWEST WINDS WILL DIMINISH THROUGH THE NIGHT, BECOMING LIGHT TO
GENTLE ACROSS MOST OF THE WATERS WITH FRESH TO STRONG GUSTS
LINGERING IN THE COASTAL JET OFF OF POINT SUR. MODERATE
NORTHWESTERLY SEAS ARE FORECAST THROUGH LATE MONDAY WITH WAVE
HEIGHTS SUBSIDING BRIEFLY ON TUESDAY. MODERATE TO ROUGH SEAS ARE
ADVERTISED MID- WEEK AND ONWARD AS NORTHWESTERLY BREEZES INCREASE.
SOUTHERLY SECONDARY SWELL WITH PERIODS OF 12 TO 16 SECONDS ARE
FORECAST WITH HEIGHTS FORECAST TO REMAIN AT OR BELOW 2 FEET.
MTR WATCHES/WARNINGS/ADVISORIES
CA...NONE.
PZ...SMALL CRAFT ADVISORY UNTIL 3 AM PDT MONDAY FOR PT ARENA TO PT
REYES 0-10 NM-PT REYES TO PIGEON PT 0-10 NM.
SMALL CRAFT ADVISORY UNTIL 9 AM PDT MONDAY FOR PT PINOS TO PT
PIEDRAS BLANCAS 0-10 NM.
SHORT TERM...BFG
LONG TERM....BFG
AVIATION...DIALH
MARINE...DIALH
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