FXUS66 KMTR 030103
AFDMTR

Area Forecast Discussion
National Weather Service San Francisco CA
603 PM PDT Wed Sep 2 2026

...New AVIATION, MARINE...

.KEY MESSAGES...
Updated at 1159 AM PDT Wed Sep 2 2026

 - Well below normal temperatures with beneficial, light rain
   chances through Thursday

 - Gradual warming and drying trend with the return of the 
   marine layer Friday into the weekend

&&

.SHORT TERM...
Issued at 1159 AM PDT Wed Sep 2 2026
(This afternoon through Thursday)

KMUX shows a band of light precipitation bisecting the Bay Area and 
moving east. Still waiting on a bucket tip south of the Golden Gate 
Bridge; nonetheless, it won't amount to much as the band continues 
to weaken. This pre-frontal rain has overperformed the official 
forecast with Mt. Tam measuring 0.57" in the last 24 hours. The 
overperformance is likely due to the struggles of guidance/models in 
the shoulder seasons. The cold frontal passage will occur tomorrow 
afternoon/evening from northwest to southeast, bringing renewed 
chances for rainfall alongside well below normal temperatures and 
cloudy conditions. This second round of rain also runs the risk of 
overperformance; however, the forecast has trended wetter. Totals of 
0.10"-0.50" for most of the North Bay and 0-0.10" south of the 
Golden Gate Bridge are expected with accumulation south of the 
Golden Gate Bridge primarily favoring the San Francisco Peninsula 
Coast. Looking at the 90th percentile, totals get bumped up with up 
to 1.00" possible in the higher terrain of the North Bay and up to 
0.50" along the San Francisco Peninsula Coast. While rainfall is 
expected to be beneficial, wet roadways will create slick driving 
conditions and increase stopping distance. Wind Advisory criteria is 
not expected to be met; however, gusts of 30-40 mph can be expected 
through gaps/passes and down the Salinas Valley.

&&

.LONG TERM...
Issued at 1159 AM PDT Wed Sep 2 2026
(Friday through next Tuesday)

A cutoff low will spawn in the Pacific Northwest from remnant upper-
level troughing as ridging expands westward into the Desert 
Southwest. The low is expected to fill through the weekend, giving 
the ridge increasing influence over the forecast. As such, a 
gradual warming and drying trend and the reformation of the marine
layer is expected over the weekend. These features will also be 
enough to shunt moisture from Tropical Storm Marie south of the 
California Bight, at least for now. Even with a cutoff low in 
play, there is relatively good agreement in the forecast through 
Monday. By Tuesday, the ECMWF and GFS begin to drastically diverge
on their solutions with Marie. The one to watch will be the ECMWF
as it has another cutoff low digging, absorbing, and bringing 
what was Marie into Central California, which would be a low 
probability outlier at the moment. It's imperative to note that if
it reaches California: 
Marie will no longer be tropical and the primary impact will be
rainfall. 

&&

.AVIATION...
(00Z TAFS)
Issued at 603 PM PDT Wed Sep 2 2026

The main forecast concern will be the passage of the cold front 
late tonight into Thursday morning. Hi-res guidance has the front 
arriving in the North Bay around 6-8Z and the gradually moving 
south. The highest chances for rain will be for the North Bay 
terminals with chances decreasing around the San Francisco Bay.
Heavier pockets of rain may bring reduced visibility at times, but 
most sites will see at least MVFR cigs with the passage of the 
front. VFR cigs may return as early as the late morning areas for 
some terminals, with better chances for lifting or clearing clouds 
by the afternoon.   

Vicinity of SFO...We'll be watching the frontal passage, which 
should reach the San Francisco area Thursday morning. The best 
chances for rain look to be between 14-20Z with perhaps some 
vicinity showers or MVFR type cigs lingering into the mid afternoon. 
Winds will be from the south early on and getting to about 15kt by 
the late morning or early afternoon. Flow becomes west/northwest 
once the front passes, with sustained 15kt winds through roughly 
sunset. Cigs should gradually improve with the frontal passage as 
well. 

SFO Bridge Approach...Similar to SFO.

Monterey Bay Terminals...The main challenge for the Monterey Bay 
region will be stratus and perhaps a rogue shower or some virga if 
the front holds up. Models show stratus trying to make a return 
after midnight but clearing shortly after sunrise. Brought cigs up a 
bit to MVFR levels rather than keeping them at IFR given last nights 
observations, but the marine layer and stratus have humbled us 
before. Nonetheless, it should be short lived as it retreats to the 
coast during Thursday morning and a front slowly meanders southward. 
VFR cigs are expected by 13-15Z Thu, with high clouds returning to 
the forecast. 

&&

.MARINE...
(Tonight through next Tuesday)
Issued at 603 PM PDT Wed Sep 2 2026

Northwesterly breezes will be light to moderate through the
remainder of the week and into the weekend with moderate wind
driven seas. Diurnal winds will increase more Friday and Saturday
afternoon, especially in vicinity of Monterey Bay. The tropical
activity well to our south will produce long period southerly
swell beginning Friday and continuing through the weekend into the
beginning of next week.

&&

.MTR WATCHES/WARNINGS/ADVISORIES...
CA...None.
PZ...None.
&&

$$

SHORT TERM...Sarment
LONG TERM....Sarment
AVIATION...KR
MARINE...JM

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Prepared by Boulder-Creek.com Weather at: Wed Sep 2 18:30:02 PDT 2026