218
FXUS66 KMTR 221125
AFDMTR
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SAN FRANCISCO CA
425 AM PDT TUE JUL 22 2025
..NEW AVIATION, MARINE
KEY MESSAGES
UPDATED AT 1234 AM PDT TUE JUL 22 2025
- COOLER THAN NORMAL THIS WEEK
- MINOR HIGH TIDE FLOODING EXPECTED THROUGH THURSDAY
SHORT TERM
ISSUED AT 1234 AM PDT TUE JUL 22 2025
(TODAY AND TONIGHT)
COOL AND HUMID CONDITIONS PREVAIL AS THE STRONG ONSHORE WINDS
EASE. A DECAYING COLD FRONT IS PUSHING THROUGH THE BAY AREA WITH
SOME CLEARING BEHIND THE BOUNDARY IN THE NORTH BAY. OTHERWISE THIS
SYSTEM WON'T BRING MUCH IMPACT TO THE SURFACE AS THE THERMAL
GRADIENT MIXES OUT ACROSS THE DECAYING FRONT. THE 850 MB
TEMPERATURE DROPPED FROM 18.55C TO 17.15C FROM 12Z TO 00Z, AND
WILL CONTINUE TO FALL OVER THE NEXT 24 HOURS AS THE COLDER AIR
MASS SETTLES IN. AN ASSOCIATED TROUGH HAS CAUSED THE MARINE LAYER
TO DEEPEN TO AROUND 3,000 FEET, WHICH WILL BRING COOL, HUMID AIR
TO ALL BUT THE HIGHEST TERRAIN ACROSS THE BAY AREA. HIGH
TEMPERATURES TODAY WILL ONLY REACH THE 70S INLAND WITH LOW 60S
ALONG THE COAST. SW WINDS ARE STILL GUSTING ABOVE 40 MPH ACROSS
GAPS AND PASSES IN THE INTERIOR EAST BAY. THIS SHOULD EASE AS THE
SFO-SAC GRADIENT HAS DECREASED TO +2.5 MB AND WILL CONTINUE TO
FALL THROUGH THE MORNING.
LONG TERM
ISSUED AT 1234 AM PDT TUE JUL 22 2025
(WEDNESDAY THROUGH MONDAY)
ALL INDICATIONS ARE THAT THE 500 MB TROUGH OFFSHORE WILL SPAWN A
CUT-OFF LOW BY WEDNESDAY. THIS WILL KEEP THE MARINE LAYER DEEP AND
TEMPERATURES COOL. THIS PATTERN WILL ALSO BRING A WEAKER GRADIENT,
AND SYNOPTICALLY FORCED ONSHORE WINDS SHOULD EASE MID-WEEK. THE
TYPICAL GUSTY LOCATIONS WILL STILL BLOW IN THE AFTERNOON, BUT ONLY
FOR A FEW HOURS AS THE DIURNAL CALIFORNIA GRADIENT BUILDS. BY THE
WEEKEND, A DEEPER TROUGH OFFSHORE WILL PICK UP THE CUT-OFF LOW.
THIS OPENS THE DOOR FOR A PATTERN CHANGE AS HIGH PRESSURE BUILDS
OVER THE DESERT SOUTHWEST. TROUGHING STILL LOOKS LIKELY OVER
NORTHERN CALIFORNIA, BUT NOT NEARLY AS ROBUST AS IN THE MEDIUM
TERM. MOST LIKELY THIS MEANS TEMPERATURES WILL START TO CLIMB
BACK TOWARD NORMAL BY THE END OF THE MONTH, AND THE ECMWF AIFS
ENSEMBLE MEAN SHOWS TEMPERATURE ANOMALIES FLIPPING FROM NEGATIVE TO
POSITIVE AROUND AUGUST 3RD.
AVIATION
(12Z TAFS)
ISSUED AT 422 AM PDT TUE JUL 22 2025
CURRENTLY A MIXED BAG OF LIFR-VFR AT THE TERMINALS. A SURFACE TROUGH
AND ITS ASSOCIATED HIGH CLOUDS IS ADDING SOME COMPLEXITY TO THE
FORECAST WITH STS YET TO DETERIORATE TO SUB-VFR, ALTHOUGH LOW
STRATUS CLOUDS ARE QUICKLY ENCROACHING (WITHIN 5 MILES OF) THE
TERMINAL. THAT BEING SAID, CONFIDENCE IS ONLY MODERATE ON ALL
TERMINALS (WITH THE EXCEPTION OF HAF) IMPROVING TO VFR BY THIS
AFTERNOON.
VICINITY OF SFO...CURRENTLY IFR WITH WESTERLY FLOW. WESTERLY FLOW
WILL PREVAIL THROUGH THE TAF PERIOD. WHILE IT IS LIKELY THAT
CEILINGS WILL IMPROVE TO VFR, THERE REMAINS A LOW PROBABILITY (10%
CHANCE) THAT SUB-VFR CEILINGS LINGER THROUGH THE TAF PERIOD.
SFO BRIDGE APPROACH...LOW STRATUS CLOUDS WILL LIKELY LINGER TO SOME
EXTENT WITHIN THE SAN FRANCISCO BAY.
MONTEREY BAY TERMINALS...CURRENTLY IFR WITH SOUTHWESTERLY FLOW AT
MRY AND IFR WITH NORTHWESTERLY FLOW AT SNS. HIGH CONFIDENCE IN
CEILINGS IMPROVING TO VFR BY THIS AFTERNOON; HOWEVER, THERE REMAINS
A LOW PROBABILITY (10%) THAT SUB-VFR CEILINGS LINGER THROUGH THE TAF
PERIOD, ESPECIALLY AT MRY. WESTERLY WINDS WILL PREVAIL THROUGH THE
TAF PERIOD.
MARINE
(TODAY THROUGH SUNDAY)
ISSUED AT 422 AM PDT TUE JUL 22 2025
A GENTLE TO MODERATE NORTHWESTERLY BREEZE AND SLIGHT TO MODERATE
SEAS WILL PREVAIL. LOW CLOUDS WITH THE POSSIBILITY OF DRIZZLE WILL
PERSIST.
CLIMATE
ISSUED AT 1221 AM PDT MON JUL 21 2025
NEW NIGHT, NEW CLIMATE FACT TO DEMONSTRATE HOW COOL THIS SUMMER
HAS BEEN. THE TABLE BELOW SHOWS HOW OFTEN SELECT CITIES TYPICALLY
HIT CERTAIN MAXIMUM TEMPERATURE THRESHOLDS FROM JUNE-JULY,
COMPARED WITH HOW MANY TIMES THAT BENCHMARK HAS BEEN REACHED SO
FAR THIS SUMMER. IF THESE NUMBERS HOLD THROUGH THE REST OF THE
MONTH, THE FINAL COLUMN SHOWS THE MOST RECENT YEAR WITH EQUAL OR
FEWER OCCURRENCES.
CITYTHRESHOLDAVG2025FEWEST SINCE
SANTA ROSA AP852491998*
SAN RAFAEL8514112022
REDWOOD CITY 80 3172008
SAN FRANCISCO701121965
HALF MOON BAY652312023
OAKLAND751541970*
LIVERMORE951232004
SAN JOSE851342004
SALINAS751101998*
PINNACLES1001331999
*FEWEST SINCE RECORDS BEGAN IN STATED YEAR
MTR WATCHES/WARNINGS/ADVISORIES
CA...COASTAL FLOOD ADVISORY FROM 8 PM THIS EVENING TO 1 AM PDT
WEDNESDAY FOR CAZ006-506-508.
PZ...NONE.
SHORT TERM...FLYNN
LONG TERM....FLYNN
AVIATION...SARMENT
MARINE...SARMENT
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