FXUS66 KMTR 161746
AFDMTR
Area Forecast Discussion
National Weather Service San Francisco CA
1046 AM PDT Wed Sep 16 2026
...New AVIATION, MARINE...
.KEY MESSAGES...
Updated at 1230 AM PDT Wed Sep 16 2026
- Cooler temperatures through Thursday
- Warming trend Friday into the weekend.
&&
.UPDATE...
Issued at 632 AM PDT Wed Sep 16 2026
The marine layer has grown to roughly 2,400 feet deep this
morning, with widespread stratus coverage. The NW wind direction
is supporting downslope drying over the Santa Cruz mountains,
which is keeping Silicon Valley clear. Otherwise the morning
clouds are reaching as far as Healdsburg, Dublin, and Pacheco
Pass. There hasn't been any measurable drizzle yet. The clouds
will start to pull back to the coast after the sun comes up.
&&
.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...
(18Z TAFS)
Issued at 1024 AM PDT Wed Sep 16 2026
An interesting stratus pattern across the region today. Stratus
should clear within the hour at STS and APC with questions as to
if OAK and SFO will clear at all today. Model guidance suggests
patchy reductions in cloud cover are possible for OAK, SFO, MRY,
and SNS with the general prevailing conditions being MVFR. Kept
the TAFs slightly more pessimistic with MVFR conditions prevailing
through the day but there may be brief periods where cloud cover
is reduced and conditions improve during the day. Breezy onshore
winds are expected this afternoon and evening with winds between
10 to 15 knots and gusts to around 25 knots at OAK and SFO. With
the marine layer deepening to 3000 ft tonight it is likely that
OVC/BKN clouds will be at a higher depth tonight. This may result
in cloud cover on the border of MVFR / VFR criteria.
Vicinity of SFO...Stratus continues to push into SFO after
clearing briefly earlier this morning. Maintained a slightly more
optimistic TAF with VFR returning this afternoon. MVFR conditions
return late tonight and prevail through tomorrow morning. Gusts to
around 25 knots are expected this afternoon.
SFO Bridge Approach...Similar to SFO.
Monterey Bay Terminals...MVFR conditions at both sites. Given the
continued push of stratus towards the interior, kept MVFR
conditions prevailing through the day at both sites. This may need
to be adjusted if cloud cover is able to break up more than
originally anticipated. Breezy westerly winds between 10 to 15
knots expected this afternoon with lighter winds overnight.
&&
.MARINE...
(Today through Monday)
Issued at 1024 AM PDT Wed Sep 16 2026
Moderate northwest to north winds prevail across the outer waters
with occasional fresh to strong gusts to diminish today. West to
southwest moderate breezes dominate over the Bays with gusts up to
25 knots resulting in hazardous conditions for small crafts late
morning through this evening. By Friday, widespread northwest to
north breezes increase to fresh with occasional strong gusts.
Wind driven rough seas to 9 to 10 feet subside to moderate by the
evening and will remain slight to moderate into the weekend.
&&
.FIRE WEATHER...
Issued at 412 AM PDT Wed Sep 16 2026
A passing trough is allowing the marine layer to expand with the
depth estimated around 2000-2500 feet in the area around the Timber
and Plaskett Fires. Above the marine layer inversion, humidities
remain low with relative humidity values as low as 15% observed. The
trend for deeper marine layers is expected to continue into Friday,
with humidities in higher elevations expected to rise as a result.
Some nocturnal drying is possible in the highest peaks, but minimal
coverage is expected.
DialH
&&
.MTR WATCHES/WARNINGS/ADVISORIES...
CA...None.
PZ...Small Craft Advisory until 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...Kennedy
MARINE...Kennedy
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Prepared by Boulder-Creek.com Weather at: Wed Sep 16 12:30:03 PDT 2026
From the National Weather Service
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