FXUS66 KMTR 041822
AFDMTR

Area Forecast Discussion
National Weather Service San Francisco CA
1022 AM PST Tue Nov 4 2025

...New AVIATION, MARINE...

.KEY MESSAGES...
Updated at 257 AM PST Tue Nov 4 2025

 - Wind gusts of 45 to 65 mph are forecast for portions of the
   North Bay, East Bay, SF Bay, and Santa Cruz Mountains.

 - Low potential for nuisance flooding in the North Bay, but
   moderate rainfall will be largely beneficial.

 - Thunderstorm chances remain around 10 to 20 percent with the
   main hazards being pockets of heavier rainfall and enhanced
   outflow winds.

&&

.UPDATE...
Issued at 905 AM PST Tue Nov 4 2025

Dense fog noted earlier this morning faded shortly after 8 AM. The
Dense Fog Advisory valid for the Salinas Valley was canceled early
as fog dissipated. 

And now we wait. It's the proverbial calm before the storm. KMUX
is currently in precip mode. It's picking up a few echoes over the
Mendo/Sonoma county line. We'll keep it in precip mode for the
day, but these scout showers ahead of the main storm will actually
lift northward. As the upper low off the coast deepens the
downstream upper level jet will push north toward the PacNW. In
response, steering flow in the lower level will be SW to NE. In
other word, scout showers will inch northward. We'll to have to
wait for the cold front later this evening and tonight more
impactful rain.  

No updates needed this morning. Will fine tune the forecast this
afternoon, but still looking more like a wind storm than a major
rain storm. 

MM

&&

.SHORT TERM...
Issued at 257 AM PST Tue Nov 4 2025 
(Today and Tonight)

Quiet weather to start the day today will transition to more
turbulent conditions tonight and into the day on Wednesday. High
clouds continue to filter in overhead across the North Bay and
this should curtail the threat for widespread dense fog (and
perhaps fog in general). Farther south, the lack of mid and upper
level clouds has facilitated more in the way of radiative 
cooling and we're starting to see some sites dip down to 1/2 mile.
Trends will be monitored this morning for a short-fused Dense Fog
Advisory (would be the SC Mountains and Salinas Valley). Fog
should mix out rapidly by mid to late morning. 

Our well advertised upper low will inch toward Northern 
California through the day. As it does, it'll induce pressure 
falls and tighten the surface pressure/height gradient. In 
response, southerly winds will ramp up, especially after 00Z 
across marine zones and adjacent coastal regions. Across the 
southern Big Sur Coast, there will likely be sufficient ascent for
some WAA convection and after discussion with LOX, opted to add 
in some showers. 

The largest impact with this system is anticipated to be the 
wind. The general timeline for winds will be from roughly 10pm
tonight through 4pm Wednesday. Over the last few days, model 
guidance has come into greater agreement with regard to placement
of the greatest corridor of winds will reside. Just about all 
deterministic guidance indicates that a belt of 50 to 60 knot flow
will nose in from the southwest across the Sonoma and Marin 
Coastline. At the surface, our trusty MTRWRF and PG&E/SJSU WRFs 
support surface wind gusts in excess of 60 mph for the Pacific 
Coast north of the Golden Gate strait and I've upgraded this 
region to a High Wind Warning for wind gusts of 60 to 65 mph which
aligns with the corridor of high 925mb winds. Taking an 
examination at some the Extreme Forecast Index tools, there's a 
very strong signal that the EPS ensemble forecast distribution is 
substantially higher than the model's climatology. In fact there's
some indication that a few of the EPS ensemble members are quite 
anomalous/extreme. What this translates to is a potential for 
65-70mph wind gusts in spots. 

Areas south of the Golden Gate are on the fringes of the 
aforementioned 925mb jet max, but wind gusts in the 45 to 55 mph
(and thus a Wind Advisory) are advertised for SF, the San Mateo 
Peninsula, East Bay, and Santa Cruz Mountains, though it's not out
of the realm of possibility that some of these areas may need to 
be added to the High Wind Warning, especially if the corridor of 
strongest winds shifts southward. Regardless of High Wind Warning
or Wind Advisory, individuals should secure any loose outdoor
articles/decor and anticipate driving difficulty for high-profile
and lightweight vehicles (especially on east-west oriented
roadways). In addition, there will be the potential for sporadic
power outages, particularly across the Pacific Coast near/north of
the Golden Gate. 

&&

.LONG TERM...
Issued at 257 AM PST Tue Nov 4 2025 
(Wednesday through Monday)

Potentially enhancing winds via precipitation loading will be
pockets of moderate to at times heavy rainfall. This will be most
probable across the North Bay where instability is forecast to be
the greatest. In fact, forecast soundings and hi-res NWP indicate
meager, but sufficient amounts of MUCAPE of around 100-250 J/kg
across the North Bay and the thunder potential is largely confined
to this region and adjacent waters. The main hazard with storms
will be bursts of stronger winds and heavier precipitation. While
heavy rainfall is possible, the potential for widespread flooding
appears to be on the low side for a couple of reasons. 1) Near 
surface soil moistures are running near or below normal per NASA 
SPoRT output, and 2) the progressive nature of this system should 
minimize the potential for training thunderstorms. Examination of 
experimental flood mapping as well as the Hydrologic Forecast 
Ensemble System indicates little to no responses across the main 
stem rivers. That said, some of the more heftier precipitation 
rates will transpire during the Wednesday morning commute and this
may result in traffic impacts as water mixes with oils in 
roadways and ponding/nuisance flooding takes place in urban/poor 
drainage areas. Again, the system appears that it'll remain 
progressive and we don't anticipate a high potential for 
stalling/training of precipitation bands.

Overall rainfall amounts remain somewhat consistent with previous
forecast iterations, though there have been some adjustments
upward in the higher terrain/favored coastal regions. North Bay 
rain amounts appear that they'll still average anywhere between 
0.50" in the 'rain shadowed' areas to the 1-2.5" range across the 
higher terrain. Some of the more prominent North Bay Mountains may
be the recipients of more optimal upslope flow with values just 
under 3". We'll need to potentially make some last minute 
refinements to QPF as there are some meaningful probabilities of 
over 3" amounts across coastal Sonoma County between Sea Ranch and
Bodega Bay. Farther south, rain amounts average between 0.25" to 
0.75" across the Bay Area and Central Coast, with amounts over 1"
across the Santa Cruz Mountains, Santa Lucia Range, and Big Sur 
Coast.

Precipitation is anticipated to taper off through Wednesday 
night. Rapid clearing in the wake of the precipitation and 
diminishing winds may set the stage for a decent radiation fog 
event, especially across the North Bay where the heaviest rainfall
is anticipated. However, this may be modulated by lingering cloud
cover, wind speeds and/or the amount of dry air that filters in 
behind a front. 

The weather pattern appears that it'll remain progressive with
largely zonal flow anticipated as we round out the first full week
of November. There are some hints at a few perturbations rippling
through the flow that may give the North Bay a few opportunities
for additional light rainfall. 

&&

.AVIATION...
(18Z TAFS)
Issued at 1021 AM PST Tue Nov 4 2025

Currently a mix of MVFR and VFR across the board. High clouds build 
in throughout the day ahead of an incoming low pressure system. For 
sites in the Bay Area - winds increase this afternoon and evening 
with peak winds expected late tonight into Wednesday morning. We are 
looking at widespread gusts between 25 kt to 40 kt across the Bay 
Area with the strongest winds along the coastline and in areas where 
terrain funneling is favored. There is the potential for stronger 
gusts than currently forecast in the 18Z TAFs to develop at HAF and 
SFO in particular. The bulk of the rain will reach the Bay Area 
tonight and continue through tomorrow morning with drops in 
visibility and ceiling heights expected. We are continuing a 10-25% 
chance of thunderstorms across the Bay Area during the day on 
Wednesday but confidence is too low to include in TAFs right now. 
Rain and strong winds will reach the Central Coast by early to mid 
Wednesday morning and continue through the rest of the day.

Vicinity of SFO...Temporary MVFR CIGs expected this morning with VFR 
to prevail the majority of the time. Main impact to SFO will be 
strong winds starting as early as 00Z (4PM) this afternoon. Guidance 
suggests winds will rapidly ramp up between 00Z-03Z with gusts to 
around 34-36 knots expected this evening. Winds further strengthen 
overnight with gusts to around 40 knots early Wednesday morning. The 
wind forecast for Wednesday morning is on the more conservative 
side. Recent WRF guidance is suggesting gusts between 45-50 knots 
are possible at SFO beginning around 12Z. If hi-res models continue 
to show gusts in the 45-50 kt range at SFO then the forecast wind 
gusts will need to be bumped up. Initial guidance is suggesting 
winds will start to ease around 20-21Z Wednesday (12PM-1PM) but if 
the system slows down at all we could see stronger winds continue 
for a longer period of time.

SFO Bridge Approach...Strong, gale force (>35 kt) winds are expected 
across the San Francisco Bay Tuesday night through Wednesday 
morning. Otherwise, similar to SFO.

Monterey Bay Terminals...VFR at MRY and SNS with strong winds, MVFR 
CIGs, and rain returning overnight into Wednesday morning. Rain 
chances increase after 12Z with showers and MVFR CIGs beginning 
between 12-15Z. Winds rapidly increase after 12Z with gusts to 
around 30 knots expected Wednesday morning. Winds remain elevated 
through the rest of Wednesday with cold frontal passage not expected 
to occur until late Wednesday/early Thursday. 

&&

.MARINE...
(Today through Sunday)
Issued at 1021 AM PST Tue Nov 4 2025

Widespread hazardous conditions to develop this afternoon before
conditions rapidly deteriorate overnight as a low pressure system
arrives. Southerly, near gale to gale force winds with widespread
gale to severe gale force gusts tonight through tomorrow morning.
Storm force gusts are expected across the northern waters from
Point  Arena to Pigeon Point. Moderate seas build, becoming rough
to very  rough, tonight through late week with significant wave
heights  between 10 to 16 feet expected. Rain chances increase
throughout the  day with moderate to heavy rain expected overnight
tonight into  tomorrow. Isolated embedded thunderstorms are
possible Wednesday  with the highest chances Wednesday morning
into the afternoon. Wave  heights abate and conditions improve by
this weekend.

&&

.MTR WATCHES/WARNINGS/ADVISORIES...
CA...Coastal Flood Advisory until 2 PM PST Saturday for CAZ006-506-
     508-529-530.

     Wind Advisory from 10 PM this evening to 4 PM PST Wednesday for 
     CAZ006-503-504-506-508>510-512-515.

     High Wind Warning from 10 PM this evening to 4 PM PST Wednesday 
     for CAZ502-505.

PZ...Small Craft Advisory from 3 PM this afternoon to 9 PM PST this 
     evening for Mry Bay-Pigeon Pt to Pt Pinos 0-10 nm-Pigeon Pt 
     to Pt Pinos 10-60 NM-Pt Pinos to Pt Piedras Blancas 0-10 nm-
     SF Bay N of Bay Bridge.

     Gale Warning from 9 PM this evening to 3 PM PST Wednesday for 
     Mry Bay-Pigeon Pt to Pt Pinos 0-10 nm-Pigeon Pt to Pt Pinos 
     10-60 NM-Pt Pinos to Pt Piedras Blancas 0-10 nm-SF Bay N of 
     Bay Bridge.

     Small Craft Advisory until 3 PM PST this afternoon for Pt Arena 
     to Pt Reyes 0-10 nm-Pt Arena to Pt Reyes 10-60 NM-Pt Reyes 
     to Pigeon Pt 0-10 nm.

     Gale Warning from 3 PM this afternoon to 9 PM PST this evening 
     for Pt Arena to Pt Reyes 0-10 nm-Pt Arena to Pt Reyes 10-60 
     NM-Pt Reyes to Pigeon Pt 0-10 nm.

     Storm Warning from 9 PM this evening to 3 AM PST Wednesday for 
     Pt Arena to Pt Reyes 0-10 nm-Pt Arena to Pt Reyes 10-60 NM-
     Pt Reyes to Pigeon Pt 0-10 nm.

&&

$$

SHORT TERM...Bain
LONG TERM....Bain
AVIATION...Kennedy
MARINE...Kennedy

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Prepared by Boulder-Creek.com Weather at: Tue Nov 4 12:30:03 PST 2025