FXUS66 KMTR 171809
AFDMTR

Area Forecast Discussion
National Weather Service San Francisco CA
1109 AM PDT Thu Sep 17 2026

...New AVIATION...

.KEY MESSAGES...
Updated at 1211 AM PDT Thu Sep 17 2026

 - Cooler temperatures through Thursday

 - Warming trend Friday into the weekend

&&

.UPDATE...
Issued at 954 AM PDT Thu Sep 17 2026

The marine layer is nearly 5,000 feet deep, which is about as deep
as it can get before mixing out. We did see some measurable
drizzle across the Bay Area this morning, but that is now 
tapering off. Cooler weather is in still on track this afternoon, 
with calmer winds than yesterday.

&&

.SHORT TERM...
Issued at 1211 AM PDT Thu Sep 17 2026
(Today and tonight)

Satellite imagery once again shows stratus hugging portions of 
the coast and beginning to move inland. As noted in the evening 
update, this isn't a classic marine layer. It has a more strato-cu
vibe due to the proximity of cold upper level low near Pt Arena. 
Do expect stratus to eventually fill in along a majority of the 
coast by sunrise. The lower heights aloft have also allowed the 
cloud deck to deepen 2500-3000 ft per profilers and ACARs 
sounding. Given the nearby low,onshore flow, and deep layer 
drizzle remains in the forecast as well. 

Outside of drizzle chances - similar to yesterday the main 
weather highlights for today will be below normal temperatures and
gusty onshore flow. Generally speaking - max temps today will be a
few warmer than yesterday, but still below seasonal averages.
Highs will top out in the 60s to near 70 along the coast and 70s
to mid 80s interior. Onshore gradients aren't overly impressive
overnight, but still seeing some gusts 30-45 mph for the Delta and
E Bay Hills. These gusty conditions will lingering through the
early morning hours before easing through the afternoon/evening
hours. 

Thursday night: the upper low begins to lose its grip on the Bay
Area as it slowly moves to the northeast. Behind the departing 
low shortwave ridging builds. A more classic marine layer will 
develop with solid stratus along the coast and inland valleys. 
Cannot rule out some patchy drizzle. 

&&

.LONG TERM...
Issued at 107 AM PDT Thu Sep 17 2026 
(Friday through Wednesday)

Friday will be a transition day as the upper low fully exits to 
the northeast and shortwave ridging builds overhead. Once the 
morning marine layer rolls back to the coast a marked warming 
trend will develop to kick off the weekend. 5-10 degrees of 
warming are expected. The warming trend will continue through 
Saturday with temperatures reaching above normal by Saturday. A 
few low 90s will return Saturday afternoon across the interior 
Central Coast. Temperatures will also get a boost on Saturday 
with a few bursts of offshore flow. Nothing overly strong, but a 
switch nonetheless. Offshore winds will be most realized over the
higher terrain of the N and E Bay. The warm up will be short-lived
as the ridge gets replaced by yet another upper low moving in from
the west on Sunday. Marine layer will likely deepen and 
temperatures cool 5-10 degrees. 

Monday and beyond is still on the lower end of confidence.
Tonight's 00Z model suite is starting to show a roller coaster of
temps next week. A slight warming up and then a slight cool down.
Uncertainty on the shoulder seasons is actually pretty common.
Cluster analysis doesn't provide a lot of additional clarity
except that models are split. Not expecting rain per se the
uncertainty is around temperatures. 

&&

.AVIATION...
(18Z TAFS)
Issued at 1046 AM PDT Thu Sep 17 2026

Low clouds will gradually scatter out into the early afternoon
hours, giving way to VFR conditions across area terminals. Light 
winds will increase this afternoon with a moderate onshore breeze 
developing. The marine layer is anticipated to return this 
evening. Latest models indicate the marine layer will compress 
overnight resulting in lower cigs overnight into Friday. 
Confidence is moderate with respect to timing and cig heights.

Vicinity of SFO... VFR cigs will gradually scatter out by the
afternoon, with a moderate onshore breeze developing in the 
afternoon. Cigs will return this evening and persist through the 
overnight hours, with moderate confidence in timing and ceilings 
height. 

SFO Bridge Approach... Similar to SFO.

Monterey Bay Terminals... VFR cigs will scatter out by early 
afternoon with a gentle west-northwest wind developing. Winds 
will ease overnight becoming light and locally variable with low 
clouds anticipated to return. Confidence in timing is moderate.

&&

.MARINE...
(Today through Tuesday)
Issued at 911 AM PDT Thu Sep 17 2026

Gentle to light breezes persist through Friday morning with mild
seas across the coastal waters. A shift occurs Friday afternoon as
northwesterly winds ramp up to fresh to strong breezes. Small
Craft Advisories take effect Friday afternoon for Monterey Bay and
the southern coastal waters from Pigeon Point south down to Point
Piedras Blancas. Winds remain enhanced through the weekend, 
maintaining hazardous conditions for small craft while overall 
seas remain light to moderate through Sunday.

&&

.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 to 9 PM PDT Friday for Pt Pinos 
     to Pt Piedras Blancas 0-10 nm.

&&

$$

SHORT TERM...MM
LONG TERM....Palmer
AVIATION...CW
MARINE...Heinlein

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Prepared by Boulder-Creek.com Weather at: Thu Sep 17 12:30:03 PDT 2026