990
FXUS66 KMTR 230441
AFDMTR
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SAN FRANCISCO CA
941 PM PDT TUE JUL 22 2025
..NEW AVIATION, MARINE
KEY MESSAGES
UPDATED AT 215 PM PDT TUE JUL 22 2025
- A 25% CHANCE FOR LIGHT RAIN SHOWERS ACROSS THE COASTAL WATERS
- MINOR HIGH TIDE FLOODING ACROSS SAN FRANCISCO BAY THRU THURSDAY
- BELOW TO NEAR NORMAL TEMPERATURES FOR THE NEXT 2 WEEKS
UPDATE
ISSUED AT 843 PM PDT TUE JUL 22 2025
THE SUN HAS SET AND THE NIGHTLY INLAND MARCH OF STRATUS IS UNDER
WAY. WHILE THERE IS A STRIP OF UPPER LEVEL CLOUDS STRETCHED ACROSS
THE BAY AREA SW TO NE, IT'S STILL EASY TO SEE SOME STRATUS
SNEAKING INLAND ON THE SATELLITE FOG PRODUCT. AS NOTED BELOW THE
MARINE LAYER WILL BE DEEP LEADING TO POTENTIAL DRIZZLE-FEST,
ESPECIALLY OROGRAPHICALLY FAVORED AREAS FOR WEDNESDAY MORNING.
THE WINDS WERE HOLLOWING THROUGH THE EAST BAY HILLS YESTERDAY
EVENING, BUT THEY'RE MUCH LESS TONIGHT. THE SFO-SAC GRADIENT IS
WEAKER, BUT STILL STRONG ENOUGH TO GENERATE GUSTS IN THE 35 MPH
RANGE. WINDS WILL CONTINUE TO EASE OVERNIGHT.
YOU'LL NOTICE THE MENTION OF SHOWERS IN THE KEY MESSAGES AT THE
TOP. WHILE NOTHING IS CURRENTLY ON RADAR THERE STILL REMAINS SOME
INSTABILITY OVER THE OFFSHORE WATERS. THE 00Z CAMS CONTINUE TO
ADVERTISE SOME OFFSHORE LIGHT NOCTURNAL SHOWERS INTO EARLY
WEDNESDAY. THE QUESTION IS HOW FAR EAST DO THEY GET IF THEY
DEVELOP? OUR CURRENT FORECAST KEEPS THEM OVER THE WATERS AND SEE
NO REASON TO CHANGE IT. NIGHT SHIFT WILL NEED TO WATCH CLOSELY AS
THEY UPDATE THE NEXT FORECAST PACKAGE.
MM
SHORT TERM
ISSUED AT 215 PM PDT TUE JUL 22 2025
(THIS EVENING THROUGH WEDNESDAY)
CONVECTION FROM EARLIER THIS MORNING HAS ALL BUT DECAYED ALONG A
SMALL CORRIDOR OF ASCENT THAT STRETCHED FROM THE BAY AREA BACK TO
THE NORTHEAST INTO THE GREAT BASIN. THIS RIBBON OF LIFT DOES
APPEAR TO STILL EXIST, BUT THE OVERALL MAGNITUDE HAS WANED WITH
THE GREATEST LIFT NOW SHIFTING EAST OF THE BAY AREA/CENTRAL COAST.
THERE REMAINS A LOWER-LEVEL REFLECTION OF THIS UPPER TROUGH STILL
AND AS A RESULT, ONSHORE FLOW CONTINUES. THIS HAS TRANSLATED TO
ENHANCED BREEZES (30-35 MPH WIND GUSTS) ACROSS GAPS, CHANNELS, AND
PASSES. OVERALL, HUMIDITY LEVELS ARE ANTICIPATED TO REMAIN ABOVE
CRITICAL CONDITIONS AND THIS WILL CURTAIL THE LARGER FIRE WEATHER
THREAT. STILL, FINE FUELS DO REMAIN CURED AND IF AN IGNITION CAN
GET GOING ACROSS ONE OF THE WIND CORRIDORS, THEN SUPPRESSION
EFFORTS MAY BE HAMPERED BY RATES OF SPREAD DUE TO THE WIND. THIS
SHOULD BE VERY LOCALIZED AND NO FIRE WEATHER HEADLINES/PRODUCTS
ARE ANTICIPATED AT THIS TIME.
HEADING INTO TONIGHT, THOUGH JUST HOW FAR THE MARINE LAYER
INVADES IS A LITTLE LESS CERTAIN. SYNOPTICALLY, BROAD 500MB
TROUGHING WILL MORPH INTO A DIFFUSE UPPER LOW THAT SHOULD PINWHEEL
SOMEWHERE NEAR THE FARALLONES. THIS WILL ENCOURAGE A LITTLE MORE
IN THE WAY OF SOUTHWESTERLY TO SOUTHERLY FLOW, EVEN DOWN TO THE
925-850MB LAYER. THE SFO-SAC MSLP DIFFERENCE OR "GRADIENT" IS
ANTICIPATED TO BE SLIGHTLY WEAKER COMPARED TO YESTERDAY AND THIS
MAY LIMIT EITHER THE DURATION AND/OR EXTENT OF STRATUS INTRUSION.
STILL THE THEME OF "NO SKY JULY" ACROSS THE IMMEDIATE COAST LINE
HOLDS TRUE AND THERE MAY NOT BE MUCH OF A CHANGE WITH REGARD TO
WEDNESDAY'S MAXT. FOR AREAS FARTHER INLAND, HOWEVER, LESS IN THE
WAY OF CLOUD COVER COULD MEAN SLIGHTLY WARMER CONDITIONS (AROUND
2-4F) ACROSS THE INTERIOR COMPARED TO TODAY, BUT IMPACTFUL HEAT IS
NOT ANTICIPATED AT THIS TIME.
SOUTHERLY TO SOUTHWESTERLY FLOW WILL ALSO ENCOURAGE DRIZZLE ALONG
THE PACIFIC COAST THROUGH ABOUT THE ENTIRETY OF THE BAY AREA AND
CENTRAL COAST. WITH THE MARINE LAYER DEPTH ESTIMATED TO BE AROUND
3,000 FEET, IT WOULDN'T BE SURPRISING TO SEE A FEW ADDITIONAL
REPORTS OF A FEW HUNDREDTHS OF AN INCH OF LIQUID IN AREA GAUGES,
ESPECIALLY ACROSS SOME OF THE FAVORED OROGRAPHIC ASCENT REGIONS
(BIG SUR COAST, SANTA CRUZ MOUNTAINS, EAST BAY HILLS, SONOMA
COASTAL RANGE). SHOWERS ARE ANTICIPATED TO REMAIN LARGELY OFFSHORE
(MAYBE A FEW ECHOES WILL DRIFT INTO COASTAL AREAS) WHERE THERE'S
A NARROW RIBBON OF HIGHER INSTABILITY (THETA-E) AIR THAT WRAPS
AROUND THE MAIN UPPER LOW. CAPE VALUES ARE UNDERWHELMING WITH
VALUES IN THE SINGLE DIGITS TO LOW TEENS AND I DON'T ANTICIPATE
WIDESPREAD RAINFALL. THAT SAID, THE RADAR SCOPE MAY BE ILLUMINATED
AND FOR THE MORNING COMMUTE, INDIVIDUALS MAY NEED TO USE THEIR
WINDSHIELD WIPERS (OR TAKE A JACKET IF COMMUTING VIA BIKE OR ON
FOOT) DUE TO DRIZZLE, SPRINKLES, OR VERY LIGHT RAIN.
LONG TERM
ISSUED AT 215 PM PDT TUE JUL 22 2025
(WEDNESDAY NIGHT THROUGH NEXT MONDAY)
THE OVERALL THEME OF COOLER TO NEAR NORMAL TEMPERATURES AND COASTAL
CLOUDINESS/DRIZZLE WILL CONTINUE THROUGH THE EXTENDED PORTION OF
THE FORECAST. CONFIDENCE IS HIGH THAT THE OVERALL SYNOPTIC REGIME
WILL REMAIN LARGELY UNCHANGED. SOME OF THE OUTLIER SOLUTIONS DO
INDICATE THAT PERHAPS THE FOUR CORNERS MID-LEVEL HIGH PRESSURE
WILL ATTEMPT TO JOG WESTWARD, BUT ONLY FOR A BRIEF AMOUNT OF TIME.
IF THIS TRANSPIRES, THEN HIGH TEMPERATURES MAY HAVE AN
OPPORTUNITY TO CLIMB ABOVE NORMAL. AT THIS TIME, HOWEVER, THAT
SUITE OF GUIDANCE THAT ADVERTISES SUCH A SOLUTION IS IN THE
MINORITY.
BROAD TROUGHING REMAINING PARKED TO THE WEST IS THE MOST
REASONABLE OUTCOME IN THE EXTENDED. AS A RESULT, ONSHORE FLOW IS
ANTICIPATED TO PERSIST, KEEPING THE HEATRISK AND THREAT OF
EXCESSIVE HEAT WELL BELOW ANY THRESHOLD NEEDED TO TRIGGER ANY
CONCERN. IN FACT, HEATRISK OUTPUT ADVERTISES ONLY MINOR TO NEAR
ESSENTIALLY ZERO THREAT FOR HEAT IMPACTING THE GENERAL POPULATION.
LONGER RANGE ENSEMBLE FORECASTS, ALBEIT THE MEANS, CONTINUE TO
INDICATE THAT THE LARGER SCALE PATTERN WILL BE DOMINATED BY WEST
COAST TROUGHING. AS SUCH, CONFIDENCE IS MEDIUM THAT THE REMAINDER
OF THE MONTH WILL LIKELY END UP BELOW NORMAL HIGH TEMPERATURE WISE
FOR MANY LOCATIONS ACROSS THE BAY AREA AND CENTRAL COAST.
AVIATION
(06Z TAFS)
ISSUED AT 941 PM PDT TUE JUL 22 2025
EXPECT LOW CLOUDS AND PATCHY DRIZZLE /MVFR-IFR/ TO MOVE INLAND
ON ONSHORE WINDS TONIGHT AND WEDNESDAY MORNING. CONDITIONS IMPROVE
TO VFR-MVFR WEDNESDAY AFTERNOON. STRATUS /MVFR/ THEN MOVES INLAND
WEDNESDAY NIGHT.
VICINITY OF SFO...MVFR TONIGHT AND WEDNESDAY MORNING, VFR WEDNESDAY
AFTERNOON WITH LOW CLOUDS /MVFR/ RETURNING EARLY WEDNESDAY NIGHT.
WEST TO SOUTHWEST WIND 5 TO 15 KNOTS.
SFO BRIDGE APPROACH...SIMILAR TO SFO.
MONTEREY BAY TERMINALS...LOW CLOUDS AND PATCHY DRIZZLE /MVFR-IFR/
TONIGHT AND WEDNESDAY MORNING. VFR-MVFR WEDNESDAY AFTERNOON. STRATUS
/MVFR/ RETURNS WEDNESDAY NIGHT.
MARINE
(TONIGHT THROUGH NEXT MONDAY)
ISSUED AT 933 PM 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 CONTINUE ACROSS THE WATERS THROUGH MID-WEEK. OTHERWISE
QUIET CONDITIONS PERSIST.
MTR WATCHES/WARNINGS/ADVISORIES
CA...COASTAL FLOOD ADVISORY UNTIL 1 AM PDT WEDNESDAY FOR CAZ006-506-
508.
PZ...NONE.
SHORT TERM...BAIN
LONG TERM....BAIN
AVIATION...CANEPA
MARINE...CANEPA
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