FXUS66 KMTR 180645
AFDMTR

Area Forecast Discussion
National Weather Service San Francisco CA
1145 PM PDT Thu Sep 17 2026

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

.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

&&

.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...
(06Z TAFS)
Issued at 1032 PM PDT Thu Sep 17 2026

A difficult forecast tonight as a well-mixed lower layer has 
practically eliminated any distinct marine layer and the clouds tend 
towards more stratocumulus than purely stratus across the region. 
Some MVFR ceilings have developed along the coast and within 
topographically favored regions. The rest of the region should 
generally expect MVFR to low-end VFR ceilings to come in through the 
night and particularly through Friday morning. 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. Friday evening, the marine layer should redevelop as 
subsidence returns to the region, and some stratus could return to 
the coastal terminals before the end of the 24-hour TAF period.

Vicinity of SFO... Transient MVFR ceilings are possible through 
around 11-12Z, when more persistent ceilings arrive at the 
terminal. The clouds should clear out around 18Z with a moderate 
west-northwest wind developing in the afternoon and evening hours.
Stratus could return to the terminal region late Friday night 
into Saturday morning, but confidence in timing is low.

SFO Bridge Approach... Similar to SFO.

Monterey Bay Terminals... Generally VFR through the next few hours 
with patches of MVFR ceilings possible near favored terrain. More 
extensive cloud coverage arrives in the early hours of Friday 
morning before the clouds diminish after sunrise. Gentle to moderate 
northwest winds will develop Friday afternoon. Friday evening, high 
resolution model output is showing stratus returning to the region, 
but confidence in development time is low. 

&&

.MARINE...
(Tonight through next Wednesday)
Issued at 1032 PM PDT Thu Sep 17 2026

West to northwest gentle breezes become moderate to fresh by
Friday 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 Friday into 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 421 AM PDT Thu Sep 17 2026

The coolest conditions and deepest marine layer are expected through 
the day today as the upper level low stalls over northern 
California. Current observations suggest a marine layer depth of 
over 3000 feet, allowing for moist conditions to reach very high 
into the higher elevations. As the low moves away on Friday, the 
marine layer will compress, temperatures will rise, and relative 
humidities in the higher elevations will start to decrease. Some 
offshore flow is possible on Saturday morning, but it is not 
expected to be very strong and the bulk of the offshore influence 
will be felt on the higher terrain of the North and East Bay.

DialH

&&

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

     Small Craft Advisory from 3 PM Friday to 3 PM PDT Saturday for 
     Pt Arena to Pt Reyes 0-10 nm.

     Small Craft Advisory from 3 PM to 9 PM PDT Friday for Pt Pinos 
     to Pt Piedras Blancas 0-10 nm.

     Small Craft Advisory from 9 PM Friday to 3 PM PDT Saturday for 
     Pt Arena to Pt Reyes 10-60 NM.

&&

$$

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

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Prepared by Boulder-Creek.com Weather at: Fri Sep 18 02:30:03 PDT 2026