Belvedere Tiburon, California Weather Forecast Discussion

608
FXUS66 KMTR 031123
AFDMTR
Area Forecast Discussion
National Weather Service San Francisco CA
423 AM PDT Fri Oct 3 2025
...New AVIATION, MARINE...
.KEY MESSAGES...
Updated at 1208 AM PDT Fri Oct 3 2025
- Strong northwesterly winds Friday, particularly along the
   coast and across higher elevations.
- Warmer and drier this weekend, with moderate offshore wind
   expected from Saturday - Tuesday.
&&
.SHORT TERM...
Issued at 1208 AM PDT Fri Oct 3 2025
(Today and tonight)
The air mass remains unstable and a few lingering showers are
tapping into this energy. There is still 100-300 J/kg of surface
based CAPE and 0.8" PW. The CAPE will decrease through the night
as the surface temperature cools and a drier air mass filters in.
That being said, there is still a chance of weak isolated showers
in the North Bay through the morning as the 500 mb low and
associated vorticity make landfall. As subtropical high pressure
builds over the NE Pacific, the skies will gradually clear
through the afternoon and evening for most outside of the
coastline south of San Francisco. This building pressure will also
create a tighter gradient with lower pressure over the
Intermountain West and generate strong NW winds over the water and
down the Salinas Valley.
&&
.LONG TERM...
Issued at 1208 AM PDT Fri Oct 3 2025
(Saturday through Thursday)
While the weather will remain nice with seasonal temperatures and
sunny afternoons through the weekend, the pattern will gradually
evolve. As the deep trough that was responsible for our disturbed
weather this week slides west of the Rocky Mountains by late
Saturday, high surface pressure will build in its wake. Meanwhile,
a weak thermal trough will develop over the Central Valley and
get nudged to the coast by a 500 mb cut-off low over the NE
Pacific. This will flip the pressure gradient and cause winds to
shift from the typical NW to an offshore N or NE direction
starting as early as late Saturday. The PGE-WRF ensemble SFO-WMC
gradient envelope bottoms out anywhere from -4 mb to -9 mb on
Monday morning. While it still looks like a moderate strength
event, the forecast trend has been gradually increasing this
gradient. Offshore winds in October can bring fire weather
concerns, but the moderate speed and recent wet weather are
mitigating factors this time. Outside of fire weather concerns, offshore
winds this time of year tend to bring really nice weather to the
Bay Area and Central Coast with warm temperatures and clear
skies.
After the offshore winds die down, another cold front is likely
late next week. GEFS IVT ensemble members all stay below 250 kg/ms
with no chance of rain through Thursday, but longer range
guidance hints that more substantial rain is possible by Friday.
4/50 ECMWF ensemble members show Santa Rosa receiving over 1" of
rain in 24 hours, with the ensemble mean near 0.25" on an
increasing trend. There is still a lot timing and intensity
uncertainty with this pattern, and a few members (18, 38, 39, 48)
don`t develop the coastal low pressure system at all and stay
totally dry next weekend.
&&
.AVIATION...
(12Z TAFS)
Issued at 415 AM PDT Fri Oct 3 2025
Weak upper level system moving out this morning. Shower activity
mostly over with, except for a slight chance this afternoon invof
North Bay terminals. Otherwise, anticipating mixed skies but
mostly clear conditions through this afternoon, aside from along
the immediate coast. Mixing of the marine layer by this upper
level system erodes some confidence in low cloud layers noted at
the end of the TAF period, but we should start to see some
recovery of shallow marine stratus by Saturday morning.
Vicinity of SFO...FEW/SCT morning clouds giving way to a mostly
clear sky through this afternoon. Some shower activity may be
visible to the north this afternoon, but currently anticipating
these will not affect the terminal.
SFO Bridge Approach...Similar to SFO.
Monterey Bay Terminals...Potential for some isolated DZ this
morning along the coast. Skies mostly clearing this afternoon, but
some degree of low cloud cover expected to linger across high
terrain south of KMRY. Expecting this cloud cover to spread
northward late tonight.
&&
.MARINE...
(Today through Wednesday)
Issued at 415 AM PDT Fri Oct 3 2025
An upper level low pressure systems continues to move ashore this
morning, promoting a few scattered showers over the waters early
this morning. Fresh to strong breeze through today, causing
widespread hazardous conditions for small craft. These winds will
support rough wind waves up to 10 feet across the outer waters
through the weekend. Winds and seas ease into the next work week.
&&
.MTR WATCHES/WARNINGS/ADVISORIES...
CA...None.
PZ...Small Craft Advisory from 9 AM this morning to 3 AM PDT Saturday
     for Mry Bay-Pigeon Pt to Pt Pinos 0-10 nm.
Small Craft Advisory until 3 AM PDT Sunday for Pigeon Pt to Pt
     Pinos 10-60 NM-Pt Arena to Pt Reyes 0-10 nm-Pt Pinos to Pt
     Piedras Blancas 0-10 nm.
Small Craft Advisory until 3 AM PDT Saturday for Pt Reyes to
     Pigeon Pt 0-10 nm.
Small Craft Advisory from 9 AM this morning to 3 AM PDT Sunday
     for Pt Arena to Pt Reyes 10-60 NM.
&&
$$
SHORT TERM...Flynn
LONG TERM....Flynn
AVIATION...Behringer
MARINE...Behringer
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NWS MTR Office Area Forecast Discussion