FXUS66 KMTR 161113
AFDMTR
Area Forecast Discussion
National Weather Service San Francisco CA
413 AM PDT Wed Sep 16 2026
...New AVIATION, MARINE, FIRE WEATHER...
.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...
(12Z TAFS)
Issued at 412 AM PDT Wed Sep 16 2026
Generally MVFR ceilings have developed across the region and are
expanding into the interior valleys. Moderate confidence that LVK
and SJC see ceilings at some point during the rest of the morning
hours. Stratus will mix out rather late in the morning, with the
coastal regions remaining socked in through the day. Some gentle to
moderate onshore winds will develop in the afternoon and evening
before MVFR stratus returns to the terminals in the evening and
overnight hours.
Vicinity of SFO... MVFR stratus lies just to the north of the
terminal area so have decided to keep the prevailing ceilings in
the TAF for now. Stratus should begin to clear out in the later
morning and early afternoon hours, but could persist to the north
of the terminal. Low to moderate confidence that OAK remains
socked in via the feed through the Golden Gate. Moderate west
winds with strong gusts will develop in the afternoon and evening
hours before MVFR stratus returns to the terminal in the evening
through the end of the TAF period.
SFO Bridge Approach... Similar to SFO.
Monterey Bay Terminals... MVFR ceilings persist through the late
morning and early afternoon hours. Gentle to moderate west winds
develop in the afternoon before diminishing in the evening. MRY sees
a brief scattering in the afternoon before stratus returns in the
early evening hours. At SNS, ceilings return a couple hours later.
&&
.MARINE...
(Today through Monday)
Issued at 412 AM PDT Wed Sep 16 2026
Moderate northwest to north winds prevail across the outer waters
as occasional fresh to strong gusts gradually diminish by the
afternoon. West to southwest moderate breezes dominate over the
Bays with strong gusts resulting in hazardous conditions for
small crafts late this morning through the evening. By Friday,
widespread northwest to north breezes increase to fresh. 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 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...DialH
MARINE...DialH
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Prepared by Boulder-Creek.com Weather at: Wed Sep 16 04:30:04 PDT 2026
From the National Weather Service
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