259
FXUS66 KMTR 211021
AFDMTR
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SAN FRANCISCO CA
321 AM PDT THU AUG 21 2025
..NEW SHORT TERM, LONG TERM, MARINE, FIRE WEATHER
KEY MESSAGES
UPDATED AT 1216 PM PDT WED AUG 20 2025
- A HEAT ADVISORY IS IN EFFECT THROUGH FRIDAY FOR MUCH OF THE
INTERIOR BAY AREA AND THROUGH SATURDAY FOR INTERIOR CENTRAL
COAST.
- TEMPERATURES WILL REMAIN ABOVE NORMAL THROUGH THE WEEKEND.
- ELEVATED FIRE WEATHER CONDITIONS ACROSS THE INTERIOR INTO THE
WEEKEND.
SHORT TERM
ISSUED AT 215 AM PDT THU AUG 21 2025
(TODAY AND TONIGHT)
PRETTY QUIET OVERNIGHT WITH MOSTLY CLEAR SKIES. SATELLITE IMAGERY
SHOWS LESS STRATUS, BUT STILL SEEING A PATCH OR TWO NEAR MONTEREY
BAY AND SF PENINSULA. OTHER ITEM OF NOTE ON THE SATELLITE IS THE
BROAD AREA OF UPPER LEVEL CLOUDS STREAMING IN FROM THE SOUTH.
MORE ON THAT LATER.
TEMPERATURES WILL BE THE BIG WEATHER IMPACT OVER THE NEXT 24
HOURS. WEDNESDAY'S INTERIOR WARMTH WAS ONLY A PREVIEW OF WHAT WE
CAN EXPECT THE NEXT FEW DAYS. THE 4-CORNERS RIDGE THAT SCORCHED
THE DESERT SW WILL MAKE ITS PRESENCE KNOWN TODAY ACROSS A LARGE
PORTION OF THE FORECAST AREA. IF YOU'RE NEAR THE COAST ONSHORE
FLOW WILL KEEP TEMPERATURES IN CHECK THANKS TO SOME NATURAL AC OFF
THE OCEAN, BUT TEMPS WILL STILL BE ABOVE SEASONAL AVERAGE. AWAY
FROM THE COAST THE WELL ABOVE NORMAL 850MB TEMPS (FORECAST TO BE
ABOVE 90TH PERCENTILE) WILL YIELD TEMPERATURES IN THE 90S TO LOWER
100S. COULD SEE A FEW RECORDS FALL AT OUR CLIMATE SITES TODAY.
THE WARMER AIR ALOFT HAS ALREADY ARRIVED, AS NOTED BY CURRENT
TEMPS IN THE 80S FOR THE HILLS. A MILD START TO THE DAY COMBINED
WITH DAYTIME INTERIOR HEAT HEATRISK VALUES WILL BE IN THE MODERATE
TO MAJOR CATEGORY TODAY. AS SUCH, HEAT ADVISORIES WILL GO INTO
EFFECT FOR INTERIOR LOCATIONS AND THE SF BAY SHORELINE. TONIGHT
WILL FEATURE ANOTHER NIGHT WITH ACTIVE THERMAL BELTS AND MILD
TEMPS IN THE HILLS WITH LITTLE RELIEF.
LONG TERM
ISSUED AT 303 AM PDT THU AUG 21 2025
(FRIDAY THROUGH WEDNESDAY)
A SLIGHT ADJUSTMENT HAS BEEN MADE FOR THE FRIDAY FORECAST.
TEMPERATURES NEAR THE COAST WILL BE WITHIN A FEW DEGREES OF
THURSDAY'S MAX TEMPS, BUT INTERIOR LOCATIONS WILL WARM A FEW MORE
DEGREES AS 850MB TEMPERATURES MAKE A RUN AT RECORD VALUES.IN SOME
CASES, FRIDAY WILL ACTUALLY BE THE HOTTEST DAY OF THIS ROUND OF
HEAT. SATURDAY WILL BE A TRANSITION DAY AS THE RIDGE BEGINS TO
EASE ITS GRIP. WHILE TEMPS BEGIN TO COOL ON SATURDAY FAR INTERIOR
LOCATIONS ARE STILL IN THE TRIPLE DIGITS, ESPECIALLY INTERIOR
CENTRAL COAST. THEREFORE, EXTENDED THE HEAT ADVISORY FOR INTERIOR
MONTEREY/SAN BENITO COUNTIES WITH HEATRISK STAYING IN THE
MODERATE TO MAJOR WITH A FEW POCKETS OF EXTREME. THIS BLENDS WELL
WITH OUR NEIGHBORING COUNTIES. TEMPERATURES WILL REMAIN ABOVE
SEASONAL AVERAGE INTO NEXT WEEK, BUT DO EXPECT A GRADUAL COOLDOWN
SUNDAY THROUGH WEDNESDAY. TEMPERATURES WILL DROP 3 TO 5 DEGREES
EACH DAY, WHICH WILL LOWER HEATRISK CONCERNS EACH DAY TOO.
NOW FOR THE WRINKLE AND WILDCARD IN THE FORECAST. THE HIGH CLOUDS
CURRENTLY STREAMING IN FROM THE SOUTH IS UPPER LEVEL MONSOONAL
MOISTURE WRAPPING AROUND THE RIDGE OF HIGH PRESSURE. MODELS
CONTINUE TO VARY ON DETAILS WITH THE MONSOONAL MOISTURE AND ITS
IMPACTS. HOWEVER, MOST SHOW SOLID UPPER LEVEL MOISTURE, DECENT
LAPSE RATES FROM 700-500MB, MUCAPE (SOME CAMS ARE VERY HIGH),
CRITICAL MODIFIED TOTAL-TOTALS, AND CLASSIC INVERTED V POINT
SOUNDINGS. ONE PIECE OF THE PUZZLE IS A MORE PRONOUNCED LIFTING
MECHANISM OR TRIGGER. AFTER COORDINATING WITH NEIGHBORING OFFICES
WILL CONTINUE TO ADVERTISE THIS AS A NON-ZERO CHANCE FOR
THUNDERSTORMS. GIVEN THE PROFILE DEVELOPED STORMS WOULD HAVE A
HIGHER CHANCE TO BE DRY. THE THREAT FOR CONVECTION STILL REMAINS
FOCUSED ON FRIDAY AND SATURDAY OVER THE CENTRAL COAST.
AVIATION
(06Z TAFS)
ISSUED AT 1002 PM PDT WED AUG 20 2025
VFR THROUGH THE TAF PERIOD. WINDS ARE REDUCING ACROSS THE REGION,
BECOMING MOSTLY LIGHT ACROSS THE REGION OVERNIGHT. SOME SPOTTY
POCKETS OF LOW CLOUDS AND FOG LOOK TO AFFECT PORTIONS OF THE COAST
OVERNIGHT AND INTO THURSDAY MORNING, BUT DON'T LOOK TO FILL OVER
ANY OF THE TAF SITES. WINDS BUILD AGAIN INTO THURSDAY AFTERNOON
BECOMING MODERATE FOR MOST AREAS AND BREEZY AT SFO. THESE WINDS
LOOK TO REDUCE AGAIN THAT EVENING.
VICINITY OF SFO...VFR THROUGH THE TAF PERIOD. WINDS HAVE REDUCED
WITH ONLY MODERATE WEST WINDS EXPECTED THROUGH THE NIGHT AND MOST
OF THE MORNING. WEST WINDS REBUILD INTO THE MID TO LATE MORNING ON
THURSDAY WITH GUSTS PEAKING AROUND 22 KTS. WINDS AND GUSTS REDUCE
AGAIN GOING INTO THURSDAY NIGHT.
SFO BRIDGE APPROACH...SIMILAR TO SFO.
MONTEREY BAY TERMINALS...VFR THROUGH THE TAF PERIOD. WINDS STAY
LIGHT THROUGH THURSDAY AFTERNOON. MODERATE WEST AND NORTHWEST
WINDS BUILD FOR THURSDAY AFTERNOON WITH SOME INFREQUENT GUSTS.
THESE WINDS BECOME LIGHT AGAIN THAT NIGHT WITH CIGS POSSIBLE
SHORTLY AFTER THE END OF THE TAF PERIOD.
MARINE
(TODAY THROUGH TUESDAY)
ISSUED AT 215 AM PDT THU AUG 21 2025
BREEZY TO GUSTY NORTHWEST WINDS WILL PREVAIL THROUGH FRIDAY
MORNING, ESPECIALLY ACROSS THE OUTER WATERS AND COASTAL JET
REGIONS NEAR POINT SUR AND POINT REYES. THIS WILL RESULT IN
WIDESPREAD HAZARDOUS CONDITIONS FOR SMALL CRAFT. WIND AND SEAS
WILL GRADUALLY EASE FRIDAY AFTERNOON AND EVENING, LEADING TO
CALMER CONDITIONS OVER THE WEEKEND AND WELL INTO THE NEXT WORK
WEEK.
FIRE WEATHER
ISSUED AT 305 AM PDT THU AUG 21 2025
WILL CONTINUE TO CARRY A HEADLINE IN THE FORECAST THROUGH THE
WEEKEND FOR ELEVATED FIRE WEATHER CONCERNS DUE TO HOT/DRY
CONDITIONS DAY/NIGHT WITH DAILY SEA BREEZE WINDS. CRITICAL
HUMIDITY VALUES WILL BE REACHED AFTERNOON WITH LITTLE TO NO
RELIEF AT NIGHT. WINDS DON'T APPEAR TO BE STRONG ENOUGH FOR AN
EXTENDED PERIOD OF TIME TO WARRANT A RED FLAG. ERC CHARTS WILL BE
RESPONDING TO THE WARM UP. IN ADDITION, WE ARE MONITORING A SURGE
OF MONSOONAL MOISTURE SET TO ARRIVE ON FRIDAY THROUGH THE WEEKEND,
WHICH WILL BRING A VERY LOW, BUT NON-ZERO, CHANCE FOR ELEVATED
CONVECTION ACROSS THE CENTRAL COAST. GREATEST CONCERN FOR ANY
DEVELOPED STORM WOULD BE DRY LIGHTNING.
MM
MTR WATCHES/WARNINGS/ADVISORIES
CA...HEAT ADVISORY FROM 10 AM THIS MORNING TO 10 PM PDT FRIDAY FOR
CAZ504-510-512>515.
HEAT ADVISORY FROM 10 AM THIS MORNING TO 10 PM PDT THIS EVENING
FOR CAZ506-508.
HEAT ADVISORY FROM 10 AM THIS MORNING TO 9 PM PDT SATURDAY FOR
CAZ516>518.
PZ...SMALL CRAFT ADVISORY FROM 3 PM TO 9 PM PDT FRIDAY FOR PIGEON PT
TO PT PINOS 0-10 NM-SF BAY N OF BAY BRIDGE.
SMALL CRAFT ADVISORY UNTIL 3 AM PDT EARLY THIS MORNING FOR PT
ARENA TO PT REYES 0-10 NM-PT PINOS TO PT PIEDRAS BLANCAS 0-
10 NM.
SMALL CRAFT ADVISORY FROM 3 PM THIS AFTERNOON TO 9 AM PDT FRIDAY
FOR PIGEON PT TO PT PINOS 0-10 NM-PT ARENA TO PT REYES 0-10
NM.
SMALL CRAFT ADVISORY FROM 3 PM THIS AFTERNOON TO 9 PM PDT FRIDAY
FOR PT PINOS TO PT PIEDRAS BLANCAS 0-10 NM.
SMALL CRAFT ADVISORY UNTIL 9 PM PDT FRIDAY FOR PT ARENA TO PT
REYES 10-60 NM.
SMALL CRAFT ADVISORY UNTIL 9 AM PDT FRIDAY FOR PIGEON PT TO PT
PINOS 10-60 NM.
SHORT TERM...MM
LONG TERM....MM
AVIATION...MURDOCK
MARINE...MURDOCK
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