043
FXUS66 KMTR 181434
AFDMTR

Area Forecast Discussion
National Weather Service San Francisco CA
734 AM PDT Fri Sep 18 2026

...New UPDATE...

.KEY MESSAGES...
Updated at 1057 PM PDT Thu Sep 17 2026

 - Warming trend Friday into the weekend

 - Brief cooldown Sunday

 - Notable warming trend next week

&&

.UPDATE...
Issued at 728 AM PDT Fri Sep 18 2026

I have to give credit to MM, he nailed the short term forecast in
the discussion below. The marine layer compressed from nearly
4,800 feet yesterday to 1,700 feet this morning. That translated
to a much lower cloud deck and even some patchy fog. While the W-E
gradients are still weakly positive, we are seeing offshore, NE
winds across the higher terrain in the North Bay and Santa Cruz
Mountains. The 0-2 km average wind from HRRR also shows NE flow
across the cwa. These trends will continue through the day
allowing much warmer and drier conditions this afternoon.

&&

.SHORT TERM...
Issued at 1057 PM PDT Thu Sep 17 2026
(Today and Tonight)

Friday will be a transition day as the upper low from the last
24-36 hrs exits to the NE. During this transition we`ll see some
clouds again Friday morning, but not in the classic marine layer
environment. More of a synoptically enhanced strato-cu set up
with lingering lift from the departing low. Regardless of the
reason, cloudy to start off the day with some patchy drizzle
possible again. For what it`s worth looking way north toward the
OR coast a more marine layer stratus deck is solidifying as the
subsidence inversion returns with building high pressure. I
digress, the low exits today and shortwave ridging is to follow
for Friday into Saturday. Shortwave ridging will kick off a brief
warming and drying trend for the Bay Area and Central Coast. Max
temps today will see a 5 to 15 degree jump from Thursday`s
readings. Not a bad way to begin the weekend with highs in the 60s
and 70s coast and 70s to upper 80s inland. As high pressure
builds in from the N and W and interior heats up we`ll see an
uptick in winds this afternoon. Strongest winds for the inland
valleys and gaps/passes with gusts of 25-35 mph.

Friday will be interesting as the marine layer tries to reform with
building high pressure, but a burst of offshore flow also
develops over the higher terrain. Not strong by any means, but
drying nonetheless. As such, think some stratus will develop
along the coast and move inland. The real battle ground will be
along the N Bay coast and N Bay Valleys where the offshore flow
may win out.

&&

.LONG TERM...
Issued at 1145 PM PDT Thu Sep 17 2026
(Saturday through next Thursday)

The warm up from Friday continues into Saturday with another few
degrees or warming. Warmest inland locations will reach the low
90s. Elsewhere lots of 70s and 80s - immediate coast 60s.

The rest of the long term is a little bit of a roller coast -
sensible weather changes, but thankfully not major impactful
changes. The shortwave ridge quickly gets replaced by a small fast
moving upper level low. The biggest change from the passing upper
low will be dropping daytime temps by up to 10 degrees. Monday
will be another transition day as the upper low exits initiating a
subtle warm up.

For the rest of next week had been rather uncertain with a variety
of model solution. A slight trend in the longwave pattern was
developing last night and tonight that trend continues. A very
notable upper level trough/low develops near the Gulf of Alaska.
Downstream of the feature a ridiculous ridge blankets the eastern
half of the CONUS with very impressive heights nosing E Canada.
This large area of high pressure also oozes westward, including
some of CA. As a result, a warming trend kicks in just in time for
the fall equinox. The peak of heat appears to happen Wednesday
and Thursday. Current forecast has far interior locations
reaching the mid to upper 90s with HeatRisk values reaching
moderate. Stay tuned...

&&

.AVIATION...
(12Z TAFS)
Issued at 429 AM PDT Fri Sep 18 2026

MVFR-IFR ceilings are coming into the region and forming along
topographically favored hillsides, with further expansion expected
through the next few hours. The cloud deck should retreat back to
the coast through the post-sunrise hours, with gentle to moderate
onshore winds expected in the afternoon and evening. The marine
layer should redevelop through the day and allow for a more typical
stratus pattern to develop overnight, although the ceilings and
timing are low confidence. Opted to not take the most aggressive
high resolution model output as gospel and kept most terminals in
IFR conditions.

Vicinity of SFO... MVFR-IFR ceilings persist through around 18Z with
a moderate west-northwest wind developing in the afternoon and
evening hours. Stratus will return to the terminal region late
tonight into Saturday morning, but confidence in the exact timing is
low.

SFO Bridge Approach... Similar to SFO.

Monterey Bay Terminals... Confidence has decreased in widespread
ceilings at the terminals as the leading edge of the cloud deck
remains offshore, but patchy radiationally-driven clouds may cause
IFR-LIFR ceilings at the terminals through the morning. Gentle to
moderate northwest winds will develop in the afternoon and evening,
with more widespread stratus coverage expected to develop in the
early evening to the overnight hours.

&&

.MARINE...
(Today through Wednesday)
Issued at 429 AM PDT Fri Sep 18 2026

Gentle west to northwest breezes become moderate to fresh by the
afternoon into the weekend. Strong gusts up to 30 kt are possible
across the northern coastal waters, Big Sur coastal jet region,
and the Monterey Bay region this morning through Saturday. Winds
gradually diminish across the southern coastal waters by Saturday
evening, but remain elevated across the north. Slight to moderate
wind driven seas persist through the weekend and steadily build to
rough by early next week.

&&

.FIRE WEATHER...
Issued at 429 AM PDT Fri Sep 18 2026

The marine layer is expected to begin redeveloping itself through
the day as a ridge develops over the state. By the evening hours the
marine layer should be around 1000-1500 feet, along with attendant
impacts of stratus development below the marine layer inversion and
poor overnight humidity recoveries within and above the thermal
belts. As the ridge develops, weak offshore flow is possible
Saturday morning, particularly across the higher elevations of the
North and East Bay.

DialH

&&

.MTR WATCHES/WARNINGS/ADVISORIES...
CA...None.
PZ...Small Craft Advisory from 3 PM this afternoon to 3 AM PDT
     Saturday for Mry Bay-Pigeon Pt to Pt Pinos 0-10 nm-Pt Pinos
     to Pt Piedras Blancas 0-10 nm.

     Small Craft Advisory from 3 PM this afternoon to 3 AM PDT Sunday
     for Pt Arena to Pt Reyes 0-10 nm.

     Small Craft Advisory from 3 PM Saturday to 3 AM PDT Sunday for
     Pigeon Pt to Pt Pinos 0-10 nm-Pt Pinos to Pt Piedras
     Blancas 0-10 nm.

     Small Craft Advisory from 9 PM this evening to 3 AM PDT Sunday
     for Pigeon Pt to Pt Pinos 10-60 NM-Pt Arena to Pt Reyes 10-
     60 NM.

&&

$$

SHORT TERM...MM
LONG TERM....MM
AVIATION...DialH
MARINE...DialH

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