651
FXUS66 KMTR 020021
AFDMTR
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SAN FRANCISCO CA
521 PM PDT TUE SEP 1 2026
..NEW UPDATE
KEY MESSAGES
UPDATED AT 107 PM PDT TUE SEP 1 2026
- COOLER WEATHER CONTINUES THROUGH THE WEEK
- BENEFICIAL WETTING RAIN EXPECTED IN THE NORTH BAY THROUGH
THURSDAY
UPDATE
ISSUED AT 517 PM PDT TUE SEP 1 2026
THE 00Z SOUNDING MEASURED THE MARINE LAYER AT 5,200 FT. THAT'S
ABOUT AS DEEP AS POSSIBLE BEFORE IT LOSES IT'S STRUCTURE. IN FACT
CUMULUS CLOUDS ARE SURVIVING WITHIN THE MARINE LAYER. THE DEEP
MARINE LAYER ALSO ALLOWED TEMPERATURES TO CLIMB HIGHER THAN
EXPECTED IN THE COASTAL AREAS. IF THE MARINE LAYER SURVIVES THE
NIGHT WE WILL SEE A DOUBLE INVERSION PATTERN. MEANWHILE LIGHT RAIN
IS APPROACHING THE NORTH BAY AND SHOULD BE THERE WEDNESDAY
MORNING.
SHORT TERM
ISSUED AT 107 PM PDT TUE SEP 1 2026
(THIS EVENING THROUGH WEDNESDAY NIGHT)
MOSTLY CLEAR SKY CONDITIONS HAVE RETURNED TO THE CENTRAL COAST
WITH SCATTERED LOW CLOUDS ACROSS THE BAY AREA AND NORTH BAY. THERE
ARE ALSO HIGH CLOUDS ASSOCIATED WITH AN APPROACHING FRONTAL
BOUNDARY ACROSS THE NORTH BAY. AS SUCH, TEMPERATURES TODAY WILL BE
5-15 DEGREES BELOW NORMAL AS THE 850 MB TEMPERATURE DROPS BELOW
10C/50F FOR THE FIRST TIME SINCE MAY. ADDITIONALLY, THERE IS A
CHANCE FOR FOR LIGHT RAIN AND/OR DRIZZLE ACROSS THE NORTH BAY
TONIGHT INTO WEDNESDAY MORNING WITH PRE-FRONATAL COASTAL DRIZZLE
FOR AREAS TO THE SOUTH.
LOW CLOUDS WILL SPREAD BACK INLAND OVERNIGHT AND INTO WEDNESDAY
MORNING WITH TEMPERATURES GENERALLY THE 50S ACROSS MUCH OF THE
REGION AND IN THE 40S IN THE HIGHER ELEVATIONS. SIMILAR CONDITIONS
ARE FORECAST FOR WEDNESDAY WITH ANOTHER DISTURBANCE MOVING IN
FROM THE NORTHWEST WEDNESDAY NIGHT INTO THURSDAY. THIS WILL BRING
INCREASING POTENTIAL FOR LIGHT RAIN ACROSS THE NORTH BAY AND
PORTIONS OF THE BAY AREA. THE GREATEST POTENTIAL TO SEE GREATER
THAN 0.25" WILL BE IN THE COASTAL RANGES OF THE NORTH BAY AND
0.10" IN AND AROUND SANTA ROSA AND THE SONOMA COUNTY VALLEYS BY
THURSDAY MORNING. RAINFALL AMOUNTS DRASTICALLY DROP OFF THE
FURTHER SOUTH YOU GO.
LONG TERM
ISSUED AT 107 PM PDT TUE SEP 1 2026
(THURSDAY THROUGH NEXT MONDAY)
HEADING INTO THIS UPCOMING WEEKEND, THERE IS THE POTENTIAL WE SEE A
SLIGHT WARMING TREND HIGH PRESSURE OVER THE CENTRAL UNITED STATES
BUILDS WESTWARD. HOWEVER, TROUGHING OFF OF THE WEST COAST WILL MAIN
COOLER THAN AVERAGE TEMPERATURES THROUGHOUT THE WEEKEND.
ENSEMBLE CLUSTERS DIVERGE HEADING INTO NEXT WEEK. AS SUCH, STILL
KEEPING AN EYE ON TROPICAL DEVELOPMENT OVER THE EASTERN PACIFIC
OCEAN FOR ANY NORTHWARD MOVEMENT OF TROPICAL MOISTURE. HOWEVER,
THE LATEST GUIDANCE IS INDICATING THE TRACK OF TS MARIE SHOULD
STAY WELL TO OUR SOUTH, POTENTIALLY BRINGING IMPACTS TO SOUTHERN
CALIFORNIA. FOR MORE INFORMATION ON TROPICAL DEVELOPMENTS VISIT
NHC.NOAA.GOV.
AVIATION
(00Z TAFS)
ISSUED AT 426 PM PDT TUE SEP 1 2026
VFR IS EXPECTED TO PREVAIL THROUGH THE REMAINDER OF TODAY AND
TONIGHT WITH MVFR CEILINGS POSSIBLE AFTER MIDNIGHT FOR THE
COASTAL TERMINALS. A FAIRLY WELL MIXED MARINE LAYER WAS MEASURED
AT ~5000FT BY THE 00Z KOAK BALLOON AND IS NOT EXPECTED TO CHANGE
MUCH THROUGH THE FORECAST PERIOD. GUSTY WINDS WILL EASE AFTER
SUNSET.
VICINITY OF SFO...VFR IS EXPECTED TO PREVAIL THROUGH THE REMAINDER
OF TODAY AND TONIGHT WITH A CHANCE FOR MVFR CEILINGS AFTER
MIDNIGHT, ESPECIALLY AT KOAK IF WINDS BECOME LIGHT AND VARIABLE,
WITH CLEARING EXPECTED AROUND SUNRISE.
SFO BRIDGE APPROACH...SIMILAR TO SFO.
MONTEREY BAY TERMINALS...MVFR CEILINGS ARE THE PRIMARY CONCERN
AFTER MIDNIGHT INTO THE EARLY MORNING HOURS WEDNESDAY, WITH VFR
EXPECTED BY MID-MORNING WITH INCREASED MIXING UNDER A ~5000FT
MARINE LAYER.
MARINE
(TODAY THROUGH SUNDAY)
ISSUED AT 915 AM PDT TUE SEP 1 2026
LIGHT NORTHWESTERLY BREEZES WILL PERSIST THROUGH THE WEEK WITH
OCCASIONAL MODERATE BREEZES. SLIGHT TO MODERATE WIND DRIVEN SEAS
WILL CONTINUE THROUGH THE WEEK WITH TROPICAL CYCLONE ACTIVITY
PRODUCING LONG PERIOD SOUTHERLY SWELL BY THE END OF THE WEEK INTO
THE WEEKEND.
MTR WATCHES/WARNINGS/ADVISORIES
CA...NONE.
PZ...NONE.
SHORT TERM...RGASS
LONG TERM....RGASS
AVIATION...JM
MARINE...JM
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