181
FXUS66 KMTR 160754
AFDMTR

Area Forecast Discussion
National Weather Service San Francisco CA
1254 AM PDT Wed Sep 16 2026

...New SHORT TERM, LONG TERM...

.KEY MESSAGES...
Updated at 1230 AM PDT Wed Sep 16 2026

 - Cooler temperatures through Thursday

 - Warming trend Friday into the weekend.

&&

.SHORT TERM...
Issued at 1208 AM PDT Wed Sep 16 2026
(Today and tonight)

Pretty easy to discern the longwave pattern over the region by
taking a peek at the water vapor imagery. A wound up upper level
low is digging over OR/CA border. The band of upper level clouds
that streamed over the Bay Area the last two days has been shunted
southward. Switching to a different satellite spectral band
quickly shows what`s happening at the surface as a result of the
upper level pattern. Satellite fog product (difference of the
10.3-3.9 um IR bands) reveals decent stratus/marine layer
coverage along the coast and pushing into the inland valleys. Per
observational data depth continues to hover in the 1100-1500 foot
range. No bucket tips as of yet, but cannot rule out some patchy
drizzle along the immediate coast. Coverage and confidence isn`t
high enough to officially include drizzle in the forecast this
morning.

Other weather highlights for Wednesday include temperatures and
wind. The dropping upper level low is ushering in some colder
850mb temperatures. Colder temperatures aloft for September
standard. As such, the airmass will support high temperatures in
the 60s at the coast and 70s with a few low 80s inland. While it
may feel nice, those values are 5 to 10 degrees below normal. The
colder airmass aloft and surface pressure gradient orientations
continue to promote gusty onshore flow this afternoon. Forecast
captures this well and highlights gusty conditions along the
coast, inland valleys, and inland gaps/passes (specifically
Altamont/Pacheco Passes). The windiest spots could see gusts up
40-45 mph. Winds will ease late in the day and more so overnight
as the onshore gradient relaxes.

For Wednesday night: given the lower 500mb heights overhead the
marine layer will deep further and exceed 2000 feet with a run
toward 2500-3000 feet by Thursday morning. Deep marine layer,
onshore flow, and enhanced orographic lift will lead to higher
confidence for widespread coastal drizzle. Despite the deeper
marine layer it`s not looking like a nocturnal drying set up,
which is good from a fire weather perspective.


&&

.LONG TERM...
Issued at 1250 AM PDT Wed Sep 16 2026
(Thursday through Tuesday)

Cloudy, cool, damp to begin the day on Thursday as the upper low
lingers over NorCal. By Friday, the cut-off low exits to the NE
with a weak shortwave ridge following for Saturday. This shift in
the upper level pattern will have a shift in the sensible weather.
The marine layer will compress slightly and temperatures will
warm.

Longer range is lower confidence as yet another upper low begins
to move through CA Monday. Expect another dip in temperatures, but
albeit brief. Thereafter, the strength of the following ridge is
uncertain. Regardless, current forecast does show warming through
the middle of next week.

&&

.AVIATION...
(06Z TAFS)
Issued at 925 PM PDT Tue Sep 15 2026

Currently a mixed bag of IFR-VFR. Stratus is at or within five miles
of all terminals and rapidly expanding. As such, all terminals are
expected to get MVFR ceilings tonight with a late-morning clearing
time. Reasonable worst case scenario is an increase in onshore winds
will delay or even prohibit clearing. Diurnal winds will prevail.

Vicinity of SFO...Currently VFR with westerly flow. Stratus is
quickly advancing and is expected to form a ceiling shortly. MVFR
conditions will likely prevail through the morning with an early
return slated for tomorrow night. Diurnal winds will prevail.

SFO Bridge Approach...Similar to SFO.

Monterey Bay Terminals...Currently MVFR with westerly flow at both
terminals. MVFR conditions will likely prevail through the morning
with an early return tomorrow night. Stratus will stick close to the
coast during the afternoon with a possibility that the terminals,
especially MRY, remain MVFR through the TAF period. Diurnal winds
will prevail.

&&

.MARINE...
(Tonight through next Monday)
Issued at 925 PM PDT Tue Sep 15 2026

Moderate northwest to northerly winds prevail across the outer
waters as occasional fresh to strong gusts gradually diminish by
Wednesday afternoon. West to southwest moderate breezes dominate
over the Bays with strong gusts resulting in hazardous conditions
for small crafts on Wednesday. By Friday, widespread northwest to
northerly breezes increase to fresh. Wind driven rough seas
subside to moderate by Wednesday evening and will remain slight to
moderate into the weekend.

&&

.FIRE WEATHER...
Issued at 345 AM PDT Tue Sep 15 2026

The transport of cooler air on northwest winds relative to sea
surface temperatures in the upper 50s to lower 60s continues to
help produce coastal stratus early this morning. The marine layer
depth varies from 1500 to 2000 feet. Above the marine layer
temperature inversion, humidities are currently in the mid 20% to
30% range. The depth of cool air transport will increase which
will gradually increase humidities at higher elevations during mid
to late week. Before humidities reach a maximum, there may be
temporary, small areas of nocturnal drying at highest elevations,
coverage though should be minimal.

&&

.MTR WATCHES/WARNINGS/ADVISORIES...
CA...None.
PZ...Small Craft Advisory from 9 AM this morning to 9 PM PDT this
     evening for SF Bay N of Bay Bridge.

     Small Craft Advisory from 3 PM this afternoon to 9 PM PDT this
     evening for Mry Bay.

     Small Craft Advisory until 3 PM PDT this afternoon for Pt Arena
     to Pt Reyes 10-60 NM.

&&

$$

SHORT TERM...MM
LONG TERM....MM
AVIATION...Sarment
MARINE...Navarrete

Visit us at www.weather.gov/sanfrancisco

Follow us on Facebook, X, and YouTube at:
www.facebook.com/nwsbayarea
x.com/nwsbayarea
www.youtube.com/nwsbayarea