Technical NOAA Weather Discussion

FXUS66 KMTR 311954
AFDMTR

Area Forecast Discussion
National Weather Service San Francisco CA
1254 PM PDT Mon Aug 31 2026

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

.KEY MESSAGES...
Updated at 1250 PM PDT Mon Aug 31 2026

 - Well below normal temperatures through Friday, gradual warming
   and drying trend this weekend

 - Beneficial wetting rain in the North Bay Tuesday through
   Thursday, drizzle/light rain possible elsewhere

&&

.SHORT TERM...
Issued at 1250 PM PDT Mon Aug 31 2026
(Monday through Friday)

Upper-level shortwave troughing will swing into Northern California 
tomorrow; this will result in temperatures well below normal, a 
chance for drizzle/light rain, and widespread cloud cover. The best 
chances for drizzle/light rain will be in the North Bay, 
particularly along the coast and in the higher terrain with the help 
of orographic lift. A reinforcing upper-level low and an attendant 
cold front will approach the area Wednesday into Thursday. This will 
keep well below normal temperatures and cloudy conditions around and 
likely make the marine layer arbitrary. There will be a better 
chance for drizzle/light rain with this round with a lifting 
mechanism in place as PWAT climbs to near one inch (90th 
percentile). It is likely (60+% chance) that the northwestern half 
of the North Bay gets wetting rain (0.10 inches) between now and 
then. While rainfall is expected to be beneficial, wet roadways will 
create slick driving conditions and increase stopping distance.

&&

.LONG TERM...
Issued at 1250 PM PDT Mon Aug 31 2026
(Saturday through Sunday)

Global ensemble clusters diverge on solutions dramatically going 
into the weekend, specifically on low vs trough and the location and 
timing of the feature, so basically everything. What is certain is 
that the region will be under the influence of some kind of 
troughing through the weekend. As it weakens through the weekend, a 
gradual warming and drying trend will commence with temperatures 
moderating to slightly below to near normal. Beyond the seven day 
forecast and into Labor Day/early next week, Invest EP95 well 
offshore of Southwestern Mexico becomes a variable. Uncertainty over 
the weekend will compound and propagate into the tropical side of 
the forecast, making it impossible to talk specific impacts at this 
point in time. The primary impacts would likely be rain and wind 
with impacts likely decreasing from south to north.

&&

.AVIATION...
(18Z TAFS)
Issued at 1156 AM PDT Mon Aug 31 2026

Finishing Fogust off strong with a robust marine layer at a depth of 
around 2200 feet this morning. MVFR stratus will take a bit longer 
to scatter out today, likely in the early afternoon. Moderate 
onshore winds increase through the day and ease slightly overnight. 
APC and LVK may experience gusts up to 20 kt through the late 
afternoon which will gradually diminish tonight. Medium confidence 
on how widespread the marine layer will be tonight as an upper level 
trough approaches our coast. This trough may generate sufficient 
lifting to mix out the marine layer across the North Bay, but 
confidence remains low. Higher confidence for coastal sites to 
develop MVFR ceilings around sunset with HAF likely to stay cloudy
all day.

Vicinity of SFO...MVFR stratus persists into the afternoon as 
moderate westerly winds increase. There has been some disagreement 
in the model guidance on whether stratus will completely scatter out 
today. Currently on satellite, there is some dry air making its way 
to our coast. This dry air combined with a moderate onshore flow 
may be enough to scatter out the remaining clouds in the SF Bay. 
MVFR ceilings return as winds ease to gentle and persist into 
Tuesday afternoon. Medium confidence on the overall forecast.

SFO Bridge Approach...Stratus is likely to become patchy over the 
bridge before scattering out at the terminals this
morning/early afternoon. Otherwise, similar to SFO.

Monterey Bay Terminals...Northwest to westerly breezes increase to 
moderate this afternoon as MVFR ceilings scatter out. The marine 
layer is less likely to mix out due to the upper level trough, 
therefore anticipate an early return of MVFR ceilings right 
around sunset. 

&&

.MARINE...
(Today through Saturday)
Issued at 1156 AM PDT Mon Aug 31 2026

Northwest to westerly gentle breezes prevail through the week and
may become moderate at times. Wind driven seas remain slight to
moderate through the week as a long period southerly swell
continues  to diminish by Tuesday.

&&

.MTR WATCHES/WARNINGS/ADVISORIES...
CA...None.
PZ...Small Craft Advisory until 3 AM PDT Tuesday for SF Bay N of Bay 
     Bridge.

     Small Craft Advisory until 9 PM PDT this evening for Mry Bay.

&&

$$

SHORT TERM...Sarment
LONG TERM....Sarment
AVIATION...Navarrete
MARINE...Navarrete

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Prepared by Boulder-Creek.com Weather at: Mon Aug 31 14:30:03 PDT 2026
From the National Weather Service