350
FXUS66 KMTR 212121
AFDMTR
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SAN FRANCISCO CA
221 PM PDT MON JUL 21 2025
..NEW SHORT TERM, LONG TERM
KEY MESSAGES
UPDATED AT 206 PM PDT MON JUL 21 2025
- BELOW NORMAL TEMPERATURES CONTINUE THROUGH THE END OF THE WEEK.
- LOCALIZED ELEVATED FIRE WEATHER THREAT FOR THE EAST BAY HILLS
THROUGH THIS EVENING DUE TO GUSTY ONSHORE WINDS.
- GUSTY ONSHORE WINDS CONTINUE THROUGH THIS EVENING ALONG THE
COAST, RIDGETOPS, AND GAPS/PASSES BEFORE EASING OVERNIGHT.
SHORT TERM
ISSUED AT 206 PM PDT MON JUL 21 2025
(THIS EVENING THROUGH TUESDAY)
STOP ME IF YOU'VE HEARD THIS ONE BEFORE - UPPER LEVEL TROUGHING AND
BELOW NORMAL TEMPERATURES CONTINUE ACROSS THE WEST COAST THROUGH THE
DURATION OF THE EXTENDED FORECAST. THE HIGH PRESSURE THAT BROUGHT
OUR TEMPERATURES CLOSER TO SEASONAL AVERAGES OVER THE WEEKEND HAS
PUSHED EASTWARD WHILE UPPER LEVEL TROUGHING DEEPENS OVER THE WEST
COAST. THIS WILL BRING US A RINSE AND REPEAT OF NO SKY JULY WITH
OVERCAST CONDITIONS RETURNING OVERNIGHT AND DISSIPATING AGAIN BY
LATE MORNING. HIGH TEMPERATURES WILL BE IN UPPER 60S TO 70S ACROSS
THE INTERIOR WITH THE HIGHER ELEVATIONS REACHING THE UPPER 70S TO
LOW 80S.
GUSTY ONSHORE WINDS PERSIST ALONG THE COAST, RIDGETOPS, AND MOUNTAIN
GAPS/PASSES THROUGH TONIGHT BEFORE DIMINISHING TUESDAY MORNING. PEAK
GUSTS BETWEEN 30 TO 40 MPH ARE EXPECTED ACROSS THE EAST BAY HILLS
WITH LOCALLY HIGHER GUSTS TO AROUND 45 MPH ACROSS THE ALTAMONT PASS
REGION. AS HAS BEEN DISCUSSED FOR THE PAST FEW DAYS, THESE STRONG
WINDS WILL RESULT IN AN INCREASED RISK OF GRASS FIRES ACROSS THE
EAST BAY. THE SFO-SAC GRADIENT LOOKS TO PEAK AROUND +4.6 HPA BETWEEN
4PM TO 8PM TONIGHT WITH GUIDANCE INDICATING THE GRADIENT WILL RELAX
OVERNIGHT. BY TUESDAY MORNING, WINDS WILL HAVE DIMINISHED ACROSS THE
REGION AND WE WILL SEE A RETURN TO OUR NORMAL DIURNAL PATTERN OF
BREEZY AFTERNOON/EVENING WINDS GUSTING BETWEEN 20 TO 30 MPH.
LONG TERM
ISSUED AT 206 PM PDT MON JUL 21 2025
(TUESDAY NIGHT THROUGH NEXT SUNDAY)
NOT TOO MANY DIFFERENCES IN THE LONG TERM FORECAST AS UPPER LEVEL
TROUGHING AND A DEEP MARINE LAYER CONTINUE. BELOW NORMAL
TEMPERATURES IN THE 70S CONTINUE ACROSS THE INTERIOR WITH THE
WARMEST LOCATIONS IN THE FAR INTERIOR EAST BAY AND INTERIOR CENTRAL
COAST REACHING THE 80S. COASTAL AREAS WILL STAY MUCH COOLER IN THE
MID 50S TO MID 60S. EXPECT A CONTINUATION OF DIURNALLY BREEZY
ONSHORE WINDS GUSTING BETWEEN 20 TO 30 MPH IN THE AFTERNOON/EVENING
AND THE RETURN OF OVERCAST SKIES EACH NIGHT WITH CLEARING EXPECTED
BY LATE MORNING. THE UPPER LEVEL TROUGH CONTINUES TO DEVELOP A CUT-
OFF LOW JUST OFFSHORE OF THE BAY AREA. THIS WILL RESULT IN AN
INCREASED CHANCE FOR THUNDERSTORM FOR OUR NEIGHBORS IN EUREKA AND
MEDFORD BUT THE THREAT IS CONFINED TO FAR NORTHERN CA/OR AND DOES
NOT IMPACT OUR CWA. NBM GUIDANCE DOES SHOW A SLIGHT WARMING TREND
STARTING NEXT SUNDAY WITH HIGHS RISING INTO THE UPPER 70S TO MID 80S
ACROSS THE INTERIOR.
THE QUESTION ON EVERYONE'S MIND, WHEN WILL WE SEE MORE SUMMER
LIKE WEATHER? WELL, CPC GUIDANCE INDICATES BELOW NORMAL
TEMPERATURES ARE LIKELY TO PERSIST THROUGH THE END OF JULY WITH A
SWITCH TO TEMPERATURES LEANING NEAR TO ABOVE NORMAL AT THE
BEGINNING OF AUGUST. LONG RANGE GUIDANCE DOES SHOW UPPER LEVEL
RIDGING PUSHING INTO THE WEST COAST AT THE START OF AUGUST WHICH
WOULD SUPPORT TEMPERATURES WARMING UP. HOWEVER, IT IS IMPORTANT TO
NOTE THAT THIS IS WELL OVER TEN DAYS OUT AND WE HAVE TO KEEP IN
MIND THAT MODEL ACCURACY DEGRADES THE LONGER IN TIME YOU GO OUT.
MODELS ARE MOST ACCURATE WITHIN THE FIRST 3 DAYS OF THE FORECAST,
ACCURACY DECREASES PAST THIS POINT BUT MODELS REMAIN DECENT
THROUGH ABOUT 7 DAYS OUT. ANYTHING PAST THE DAY 7 MARK SHOULD BE
USED FOR TREND GUIDANCE AND NOT TAKEN AS A REPRESENTATION OF WHAT
WILL EXACTLY HAPPEN. SO IS IT GUARANTEED WE WILL SEE WARMER
TEMPERATURES COME AUGUST? NO, BUT IT'S WORTH KEEPING AN EYE ON THE
FORECAST TO SEE HOW GUIDANCE EVOLVES AND IF MODELS ARE
PERSISTENTLY SHOWING RIDGING OR TROUGHING OVER THE WEST COAST.
AVIATION
(18Z TAFS)
ISSUED AT 1019 AM PDT MON JUL 21 2025
DEEP MARINE LAYER WITH IFR/MVFR STRATUS PERSISTS THROUGH MUCH OF
THE TAF PERIOD WITH A FAIRLY CONSISTENT DIURNAL MIX OUT TO VFR
DURING THE AFTERNOONS. WEAK COLD FRONT BRINGING SCATTERED DZ TO
THE REGION THIS MORNING, WHICH WILL GIVE WAY TO MOSTLY CLEAR SKIES
THIS AFTERNOON INLAND. LOCATIONS MORE NEAR THE COAST AND IMMEDIATE
BAY AREA WILL SEE STRATUS LINGERING INTO THE EARLY AFTERNOON AND
MAKING AN EARLY RETURN THIS EVENING THANKS TO THE VERY DEEP MARINE
LAYER AND ROBUST ONSHORE FLOW.
VICINITY OF SFO...CURRENTLY MVFR STRATUS WITH A FEW BREAKS VISIBLE
IN THE CLOUD DECK VIA VISIBLE SATELLITE. NOT EXPECTING THESE
BREAKS IN THE CLOUDS TO HAVE MUCH EFFECT ON MIXING OUT THE CLOUD
DECK THANKS TO ROBUST ONSHORE FLOW AND VERY DEEP MARINE LAYER.
MODERATE CONFIDENCE THAT THE AREA INVOF THE SF BAY WILL SEE SOME
ASPECT OF VFR THIS AFTERNOON BEFORE AN EARLY RETURN TO MVFR THIS
EVENING.
SFO BRIDGE APPROACH...SIMILAR TO SFO.
MONTEREY BAY TERMINALS... EARLIER CLEARING TO VFR THAN ANTICIPATED
THIS MORNING THANKS TO A COASTAL EDDY THAT FORMED IN THE MONTEREY
BAY, WHICH HELPED MIX IN SOME DRIER AIR FROM ALOFT. THIS PATTERN
MAY WAFT CLOUDS ACROSS THE AREA THROUGH THE AFTERNOON, BUT LARGELY
EXPECTING TERMINALS TO REMAIN MOSTLY VFR INTO THE LATE AFTERNOON.
THE EXCEPTION BEING KWVI WHERE CIGS ARE MORE UNIFORM AND ONSHORE
FLOW IS DIRECT.
MARINE
(TODAY THROUGH SATURDAY)
ISSUED AT 930 AM PDT MON JUL 21 2025
MODERATE BREEZES ARE EXPECTED TODAY, RESULTING IN HAZARDOUS
BOATING CONDITIONS FOR SMALLER VESSELS IN THE NORTHERN SAN
FRANCISCO AND SAN PABLO BAYS AND ACROSS THE NORTHERN OUTER
WATERS. SLIGHT TO MODERATE SEAS PERSIST THROUGH THE REMAINDER OF
THE FORECAST PERIOD. WINDS EASE TUESDAY THROUGH LATE WEEK.
CLIMATE
ISSUED AT 1221 AM PDT MON JUL 21 2025
THIS SUMMER HAS BEEN COOLER THAN AVERAGE AND THAT TREND WILL
CONTINUE FOR AT LEAST ANOTHER WEEK. I DECIDED IT WAS A GOOD TIME
TO ADD A CLIMATE SECTION HERE TO COMPARE JUST HOW DIFFERENT THIS
SUMMER HAS BEEN THAN LAST YEAR. I CREATED A SIMPLE HEAD-TO-HEAD
SCORING SYSTEM TO ADD DAYS ABOVE/BELOW NORMAL WEIGHTED BY HOW FAR
ABOVE/BELOW NORMAL THEY WERE. FOR EXAMPLE, IF THE MAXIMUM
TEMPERATURE WAS 2 DEGREES BELOW NORMAL ON SATURDAY AND 3 DEGREES
ABOVE NORMAL ON SUNDAY, THE SCORE WOULD BE 2-3. I FOCUSED ON MAX
TEMPERATURE AT SAN JOSE FROM JUNE 1 - JULY 20. METEOROLOGICAL
SUMMER STARTS JUNE 1ST AND SAN JOSE IS A GOOD MIXTURE OF SOME
MARINE LAYER INFLUENCE AND INLAND HEAT DEPENDING ON THE DAY.
AGAIN, I JUST MADE THIS SCORING SYSTEM UP TONIGHT, SO HOPEFULLY IT
MAKES SENSE. THE RESULTS ARE PRETTY INTERESTING, PARTICULARLY
WHEN COMPARED WITH LAST YEAR.
2025: COLD: 168, WARM: 36
2024: COLD: 30, WARM: 302
MTR WATCHES/WARNINGS/ADVISORIES
CA...COASTAL FLOOD ADVISORY FROM 7 PM THIS EVENING TO MIDNIGHT PDT
TONIGHT FOR CAZ006-506-508.
PZ...SMALL CRAFT ADVISORY UNTIL 9 PM PDT THIS EVENING FOR SF BAY N OF
BAY BRIDGE.
SMALL CRAFT ADVISORY UNTIL 9 PM PDT THIS EVENING FOR MRY BAY-
PIGEON PT TO PT PINOS 0-10 NM-PT PINOS TO PT PIEDRAS
BLANCAS 0-10 NM.
SHORT TERM...KENNEDY
LONG TERM....KENNEDY
AVIATION...BEHRINGER
MARINE...BEHRINGER
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