938
FXUS66 KMTR 201810 AAA
AFDMTR

Area Forecast Discussion...UPDATED
National Weather Service San Francisco CA
1110 AM PDT Sun Jul 20 2025

...New AVIATION...

.KEY MESSAGES...
Updated at 133 PM PDT Sat Jul 19 2025

 - Cooling trend begins Monday with a widespread return to below
   normal temperatures.

 - Localized elevated fire weather threat for the East Bay Hills
   Sunday and Monday due to dry conditions and gusty winds.

 - Gusty winds return late Sunday and continue through Monday
   along the coast, the higher terrain, and mountain gaps/passes.

&&

.UPDATE...
Issued at 914 AM PDT Sun Jul 20 2025

Stratus coverage, while still widespread, is a bit more patchy
across the Bay Area than it was yesterday morning. The 12Z OAK
sounding shows the marine layer compressed to around 1500 feet
overnight which would help explain why the stratus coverage was
patchier. Pockets of diminished visibility along the coast have
started to improve with further improvement expected as stratus
clears by mid to late morning. Gusty winds remain on track to
develop this afternoon/evening with the only adjustment to the

&&

.SHORT TERM...
Issued at 217 AM PDT Sun Jul 20 2025
(Today and tonight)

The forecast for the most part is starting to sound like a broken
record: morning stratus layer clearing to the coast by the
afternoon with seasonably cool temperatures. While the overall
weather picture is the same there are some details that differ:
high temps, marine layer depth, and winds. The upper level ridge
that brought some inland warmth Saturday has weakened and is being
replaced by an upper level trough/lower 500mb heights. The
overnight satellite fog product shows the marine layer has better
coverage than 24 hours due to the building upper level trough.
Have added some coastal drizzle/patchy fog to the forecast given
the current marine layer set up. The upper level trough will also
help to knock inland temperatures down a few degrees. The biggest
weather change for today will be the winds. For several days now
we`ve been mentioning increasing winds late Sunday into Monday.
Latest guidance continues to advertise a solid push of winds. In
fact, onshore gradients (SFO-SAC) are projected to be 4 to 5 mb
later this afternoon and evening yielding some robust winds for
the East Bay gaps/passes and West Delta region. Borderline for a
wind advisory, but gusts in the 30-40 mph with a few isolated up
to 50 mph will be possible. It will be windy along the coast,
higher terrain, and favored valleys, but not as strong as the East
Bay.

It goes with out saying, but the uptick in winds will create
increased fire weather concerns for the East Bay. While winds
increase humidity values are lowering to the 25-40% range. While
not critical RH the wind will override it. ERC chart values take
a dip today the more wind based index of the Burn Index reaches in
the 90th percentile. So that means, flashier fuels and more
flammable live fuels could carry fire. Speaking of fire weather
concerns a classic nocturnal drying event is taking place over
the Santa Lucia range. As stratus rolled through the Salinas
Valley rapid drying occurred above it with a sensor on Chews
Ridge dipping into the single digit RH.

Sunday night into Monday: Solid onshore flow remains with breezy
conditions lingering in the East Bay. The marine layer will
deepen with more coastal drizzle.

&&

.LONG TERM...
Issued at 254 AM PDT Sun Jul 20 2025
(Monday through Saturday)

To kick off another work week more of the same - night/morning
clouds with afternoon inland sunshine. Onshore winds ease
slightly early Monday before ramping back up Monday
afternoon/evening favoring the inland gaps/passes.

Thereafter pretty benign weather continues into next weekend.
Marine layer is locked in with cooler the seasonal temperatures
thanks to an anomalously low upper level trough overhead. Some
longer range guidance even deepens the trough and has an a cut-
off low form over the region by Thursday. Simply put, if you`re
enjoying the cooler weather with some afternoon sunshine you`ll
enjoy the long term forecast.

&&

.AVIATION...
(18Z TAFS)
Issued at 1105 AM PDT Sun Jul 20 2025

Largely a persistence forecast for the terminals with VFR
anticipated at most sites (except KHAF) this afternoon before MVFR
to LIFR stratus returns this evening and into the overnight hours.
Confidence in the forecast is medium to high, though there are
the usual nuisances due to terrain and offshore eddy formation.
KAPC may be the beneficiary of an eddy just east of the GG gap
and clearing will be later compared to some of the other terminals.
Otherwise, onshore flow will translate to wind gusts near 25
knots at the terminals nearest the SF/San Pablo Bays. Onshore flow
tonight into Monday will usher in another round of marine stratus
at all terminals. The current KOAK TAF indicates MVFR, as the
window for IFR seems to be short-lived and confidence isn`t quite
high enough to include, yet. Confidence is high that by 0900 UTC,
just about all TAFs will be inundated with stratus. Reduced
visibility should be anticipated at KSTS and KHAF due to BR/DZ.
With the onshore flow remaining persistent, VFR may not return
until 1700 UTC or after at the coastal terminals.

Vicinity of SFO...There remains an opportunity for occasional
MVFR cigs through 1900 UTC today, but the afternoon will largely
be VFR. Wind gusts increase up to around 25 knots by 2100 UTC and
persist through the early evening. Some guidance (4 out of 10
models) offer an early onset of MVFR stratus and potential loss of
VAPS as early as 0300 UTC. For now, will lean a bit more on climo
which supports MVFR around 0600 UTC. If MVFR ceilings do arrive
earlier, the evening push may be impacted. Similar to KOAK, the
chances for IFR cigs is non-zero, but not high enough to include
in the TAF at this time. Impacts to the Monday morning push are
highly probable with MVFR lingering through the noontime hour. The
current TAF set is a little pessimistic on the back end with MVFR
through Monday mid-afternoon, however, trends in satellite and
model guidance will be monitored for refinements.

SFO Bridge Approach...Satellite and webcam imagery support VAPS
and this will likely continue through the afternoon/evening. MVFR
will return between 0600-0800 UTC with ILS operations likely
warranted through at least late Monday morning.

Monterey Bay Terminals...Stratus continue to quickly erode late
this morning and VFR should be anticipated through at least 00
UTC. Near or shortly after, MVFR/IFR stratus will return with
LIFR cigs by 0600 UTC. A few instances of LIFR at KSNS are
expected to transpire just prior to 0600 UTC as flow responses to
the diurnal heating/cooling across the region. IFR visibility is
also most probable at KMRY as convergence leads to meager lift
along the marine/land interface. VFR does not appear likely until
after 1700 UTC Monday.

&&

.MARINE...
(Today through Friday)
Issued at 914 AM PDT Sun Jul 20 2025

Moderate breezes to near-gale force wind gusts are forecast today
and into Monday. This will result in hazardous boating conditions
for smaller vessels near and across the northern San Francisco
and San Pablo Bays. Hazardous boating conditions should also be
anticipated across northern outer waters beyond 10 nautical miles
from the shore. In addition, northwesterly coastal jets with
strong breezes are anticipated this afternoon across northern
Monterey Bay and near Point Sur. These strong breezes will persist
into the pre-dawn hours on Monday across the Big Sur coastline.
Slight to moderate seas persist through the remainder of the
forecast period. Winds ease some through Tuesday, except across
southern portions of the Big Sur coast, where strong northwesterly
breezes persist. Otherwise, reduced visibility should be
anticipated during the morning hours due to fog/drizzle.

&&

.MTR WATCHES/WARNINGS/ADVISORIES...
CA...None.
PZ...Small Craft Advisory until 9 PM PDT Monday for SF Bay N of Bay
     Bridge.

     Small Craft Advisory from 3 PM to 9 PM PDT Monday for Mry Bay-
     Pigeon Pt to Pt Pinos 0-10 nm-Pt Pinos to Pt Piedras
     Blancas 0-10 nm.

     Small Craft Advisory until 9 AM PDT Monday for Pt Arena to Pt
     Reyes 0-10 nm-Pt Arena to Pt Reyes 10-60 NM.

&&

$$

SHORT TERM...MM
LONG TERM....MM
AVIATION...Bain
MARINE...Bain

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