FXUS66 KMTR 132254
AFDMTR

Area Forecast Discussion
National Weather Service San Francisco CA
354 PM PDT Sun Sep 13 2026

...New AVIATION, MARINE...

.KEY MESSAGES...
Updated at 1056 AM PDT Sun Sep 13 2026

 - Breezy onshore winds this afternoon becoming lightly offshore
   overnight

 - Gustier, dry offshore winds across the Vaca Range and Altamont
   Pass tonight into Monday

&&

.SHORT TERM...
Issued at 1056 AM PDT Sun Sep 13 2026
(This afternoon through Monday)

Troughing continues to dominate the forecast as a deep upper level 
low continues to move through the PNW and into the Intermountain 
West. The marine layer remains at a depth of approximately 1500 ft 
but dry air in the wake of last night's dry cold frontal passage 
prevented stratus from redeveloping across the interior last night. 
The drier airmass is expected to remain in place through at least 
midweek with another night of largely clear skies expected tonight. 
Patchy stratus is possible directly along the coastline where 
conditions are more supportive for stratus development. Wondering 
why? Buoys are reporting warmer ocean temperatures than air 
temperatures above it. This indicates an upwards transfer of 
heat/moisture from the ocean to the air, resulting in a warming and 
saturating layer of air where stratus is able to develop. Any 
coastal stratus that does develop will be patchier with the San 
Mateo coastline and coastal Monterey Peninsula the most likely areas 
to see at least temporary cloud cover overnight. 

Another factor in tonight's stratus forecast is the wind. Winds 
through this evening will be breezy and onshore with the SFO-WMC 
gradient forecast to peak around +9 to +10 mb today. This largely 
correlates to wind gusts between 20 to 35 mph with gusts up to 45 
mph across the favored windy spots. By tonight the wind setup 
changes from onshore to offshore. Offshore winds should remain on 
the lighter but two locations, the highest ridgelines of the Vaca 
Mountains and the Altamont Pass, will experience gustier offshore 
winds between 20 to 35 mph overnight tonight through Monday. 
Offshore winds will keep the region slightly drier overnight which
increases confidence that stratus will struggle to 
redevelop/spread across the interior tonight. That being said, not
anticipating any major fire weather concerns given the short 
duration and localized nature of the stronger offshore.

A slight warming trend will kick off Monday as the center of the 
upper low moves into the Intermountain West and more zonal flow 
dominates Central California. This will see a return of near normal 
temperatures for much of the region with interior highs in the 80s 
and coastal areas in the 60s to 70s. The hottest locations (far 
interior East Bay and interior Central Coast) will reach the upper 
80s to potentially the 90 degree mark. Winds to decrease throughout 
the day with light to moderate onshore winds returning during the 
day.

&&

.LONG TERM...
Issued at 1056 AM PDT Sun Sep 13 2026
(Monday night through next Saturday)

Zonal flow to slight troughing continues through midweek before 
another deeper trough pushes into the Oregon and Northern California 
border. Temperatures remain relatively seasonal on Tuesday with 
highs in the upper 70s to 80s across the interior and 60s along the 
coastline. The arrival of the upper level trough will bring a cooler 
airmass into the Bay Area and Central Coast with 850 mb temperatures 
peaking around 12 C during the day. That is roughly between the 10th 
and 25th percentiles for this time of year with the median 850 mb 
temperature ~17 C. The NBM was running a bit warmer than other 
models for Wednesday/Thursday but the latest run has started to 
lower temperatures, coming into better agreement. A reasonable lower 
end temperature forecast for Wed/Thurs would be interior highs in 
the low to mid 70s while the higher end forecast (the current 
forecast) keeps high temperatures in the mid 70s to low 80s. Given 
the arrival of the much cooler airmass, would not be surprised if we 
saw the forecast high temperatures for Wed/Thurs to decrease by a 
few more degrees (slightly closer to the lower end forecast). The 
caveat to this being temperatures may be warmer if the trough/cold 
air mass slows down and arrives later than currently forecast. 
Regardless, the cool down will be most evident Wednesday and 
Thursday with near normal temperatures in the upper 70s to mid 80s 
Friday into the weekend. The arrival of the trough should allow the 
marine layer to deepen enough that stratus will become more 
widespread mid to late week. Diurnally breezy winds continue across 
mountain gaps and passes, the coast, and along the highest 
ridgelines. Northern California and the Sierra Range have some 
potential for thunderstorms mid to late week as the trough moves in 
but chances are negligible across our region (<5%) with 
thunderstorms not expected.

&&

.AVIATION...
(00Z TAFS)
Issued at 353 PM PDT Sun Sep 13 2026

Currently VFR with gusty onshore winds, this will continue through 
the evening. Low confidence on sub-VFR conditions returning tonight 
due to the combination of persistence, windier conditions, and 
offshore flow tonight. If stratus forms, it'll likely be on the cusp 
of IFR/MVFR and remain confined to the coast with a later than 
normal arrival and early than normal clearing. Diurnal winds will 
prevail.

Vicinity of SFO...Currently VFR with westerly flow. Gusts of 30 
knots can be expected through 04Z before westerly winds diminish 
overnight. High confidence on VFR and diurnal winds prevailing 
through the TAF period.

SFO Bridge Approach...Similar to SFO.

Monterey Bay Terminals...Currently VFR with westerly flow at both 
terminals. Persistence and windier conditions has led to decreasing 
confidence in ceilings on the cusp of IFR/MVFR returning tonight. If 
one forms, it'll likely be relatively late to arrive and early to 
scatter out. Diurnal winds will prevail.

&&

.MARINE...
(Tonight through next Friday)
Issued at 353 PM PDT Sun Sep 13 2026

Widespread hazardous conditions for small craft will continue
tonight with gale force gusts along the Big Sur Coast and in
Monterey Bay. Tomorrow will be similar with widespread hazardous
conditions for small craft with gale force gusts across the
northern waters. Conditions begin to improve Tuesday as
northwesterly breezes diminish with that trend continuing through
Thursday. Moderate to rough seas will prevail through Tuesday
before abating Wednesday.

&&

.FIRE WEATHER...
Issued at 422 AM PDT Sun Sep 13 2026

Patchy coastal stratus has developed overnight. 925 mb relative 
humidities are higher over the Timber and Plaskett fires early 
this morning. Tonight into Monday night, a light to gentle 
offshore breeze (with occasionally moderate gusts) is forecast to 
develop in the higher terrain as the mid/upper level trough axis 
shifts into the northern Rockies. As such, areas above the marine 
layer often experience nocturnal drying that will likely continue 
through early this upcoming week.

&&

.MTR WATCHES/WARNINGS/ADVISORIES...
CA...None.
PZ...Small Craft Advisory until 9 PM PDT this evening for SF Bay N of 
     Bay Bridge.

     Gale Warning until 9 PM PDT this evening for Mry Bay-Pigeon Pt 
     to Pt Pinos 0-10 nm.

     Small Craft Advisory until 3 AM PDT Monday for Pt Arena to Pt 
     Reyes 0-10 nm-Pt Reyes to Pigeon Pt 0-10 nm.

     Small Craft Advisory from 3 PM Monday to 3 AM PDT Tuesday for Pt 
     Arena to Pt Reyes 0-10 nm.

     Gale Warning until 3 AM PDT Monday for Pt Pinos to Pt Piedras 
     Blancas 0-10 nm.

     Small Craft Advisory until 3 AM PDT Tuesday for Pigeon Pt to Pt 
     Pinos 10-60 NM-Pt Arena to Pt Reyes 10-60 NM.

&&

$$

SHORT TERM...Kennedy
LONG TERM....Kennedy
AVIATION...Sarment
MARINE...Sarment

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Prepared by Boulder-Creek.com Weather at: Sun Sep 13 18:30:03 PDT 2026