Technical NOAA Weather Discussion

FXUS66 KMTR 010519
AFDMTR

Area Forecast Discussion
National Weather Service San Francisco CA
1019 PM PDT Mon Aug 31 2026

...New AVIATION, MARINE...

.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...
(06Z TAFS)
Issued at 1019 PM PDT Mon Aug 31 2026

MVFR stratus has lingered through the day across portions of the SF 
Bay Area, and is beginning to expand again across the North Bay and 
into the Monterey Bay region. High clouds may interrupt the 
radiational cooling across portions of the South Bay and Central 
Coast, but a very deep marine layer should support stratus decks 
heading far inland through the course of the night. Stratus should 
clear back to the immediate coast through the course of Tuesday 
morning into the early afternoon, with a gentle to moderate onshore 
pattern wind developing in the afternoon and evening hours. Tuesday 
night, lower confidence in stratus impacts as the fringes of a 
decaying front begin to impact the region, with a shift to a more 
southwest wind flow expected as the front or its remnants approach. 
Chances for rain in the North Bay lie just after the end of the 24-
hour TAF period.

Vicinity of SFO... MVFR stratus with gentle southwest winds through 
the night and into Tuesday morning. Moderate confidence in a 
moderate westerly breeze developing in the afternoon and evening 
hours on Tuesday, with winds turning to the southwest and the south 
through the evening and overnight periods. Low confidence of MVFR 
ceilings Tuesday night before the end of the TAF period, with 
greater confidence in low-end VFR clouds over the terminal.

SFO Bridge Approach... Similar to SFO.

Monterey Bay Terminals... MVFR to low-end VFR ceilings persist 
through the latter part of Tuesday morning. A gentle onshore wind 
persists through the afternoon and evening, with the winds turning 
from the southwest over MRY tonight to the west for the afternoon 
and evening. Low confidence in a return of stratus to SNS Tuesday 
night as winds diminish.

&&

.MARINE...
(Tonight through next Sunday)
Issued at 1019 PM PDT Mon Aug 31 2026

Gentle westerly to northwesterly breezes persist through the week
with intermittent periods of moderate breezes. Wind driven seas
remain slight to moderate through the week with long period
southerly swells persisting thanks to tropical cyclone activity.

&&

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

&&

$$

SHORT TERM...Sarment
LONG TERM....Sarment
AVIATION...DialH
MARINE...DialH

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Prepared by Boulder-Creek.com Weather at: Mon Aug 31 22:30:03 PDT 2026
From the National Weather Service