460
FXUS66 KMTR 221645
AFDMTR
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SAN FRANCISCO BAY AREA
ISSUED BY NATIONAL WEATHER SERVICE LOS ANGELES/OXNARD CA
945 AM PDT TUE JUL 22 2025
..NEW UPDATE, MARINE
KEY MESSAGES
UPDATED AT 1234 AM PDT TUE JUL 22 2025
- SPRINKLES OR LIGHT RAIN THIS MORNING AND AFTERNOON
- MINOR HIGH TIDE FLOODING EXPECTED THROUGH THURSDAY
- COOLER THAN NORMAL THIS WEEK
UPDATE
ISSUED AT 831 AM PDT TUE JUL 22 2025
OVERALL THE SHORT TERM FORECAST IS IN GOOD SHAPE WITH JUST
A FEW TWEAKS TO THE POP/WX GRIDS THIS MORNING.
A BAND OF MODEST ASCENT, PER GOES SATELLITE IMAGERY, EXTENDS FROM
NEAR THE GREAT BASIN BACK TO THE SOUTHWEST INTO THE BAY AREA.
THERE IS A REFLECTION OF THIS BAND OF ASCENT IN SOME OF THE LOWER
HEIGHT FIELDS WITH MODEST CAA IN ITS WAKE. THE 12 UTC OAK RAOB
INDICATED A PW OF JUST OVER 1 WHICH IS ABOVE THE 90TH PERCENTILE
FOR THIS TIME OF YEAR. THIS IS AROUND 1/2 GREATER PW THAN OUR 00
UTC RAOB. MOIST ADVECTION IN TANDEM WITH ASCENT HAS ACTUALLY
RESULTED IN RADAR RETURNS AND A FEW REPORTS OF SPRINKLES AND LIGHT
RAIN HAVE BEEN RECEIVED. THIS TREND IS ANTICIPATED TO CONTINUE
INTO THE AFTERNOON HOURS AND POP AND WX GRIDS WERE FINE-TUNED TO
ACCOUNT FOR ONGOING TRENDS AND SHORT TERM EXPECTATIONS. ALL IN
ALL, NO SIGNIFICANT IMPACTS ARE ANTICIPATED OTHER THAN SOME
SLIGHTLY DAMP ROADS AND SURFACES.
OTHERWISE, MINOR COASTAL FLOODING SHOULD BE ANTICIPATED ACROSS THE
IMMEDIATE SAN FRANCISCO BAY AREA DUE TO HIGHER THAN NORMAL HIGH
TIDES THROUGH AT LEAST MIDNIGHT TONIGHT. IMPACTS WILL BE CONFINED
TO AREAS IMMEDIATELY ALONG THE BAYSHORE LINE SUCH AS COASTAL
TRAILS AND OTHER RECREATIONAL AREAS. BE SURE TO AVOID FLOODED
AREAS.
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 831 AM PDT TUE JUL 22 2025
A GENTLE TO MODERATE NORTHWESTERLY BREEZE AND GENERALLY LOW SEAS
CONTINUE THROUGH THIS WEEK. LOW CLOUDS WITH THE POSSIBILITY OF
DRIZZLE ACROSS THE WATERS THROUGH MID-WEEK.
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
.TDAY...NONE.
PUBLIC FORECAST:
AVIATION/MARINE:
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