899
FXUS66 KMTR 040443
AFDMTR

Area Forecast Discussion
National Weather Service San Francisco CA
943 PM PDT Sun Aug 3 2025

...New AVIATION, MARINE...

.KEY MESSAGES...
Updated at 1155 AM PDT Sun Aug 3 2025

 - Elevated breezes across channels, gaps, passes, and across the marine
   environment through Monday.

 - Elevated fire weather threat for wind corridors and portions of
   the Santa Lucia Range through Monday and again late this week.

 - Subtle warming trend expected through midweek with pockets of
   moderate HeatRisk across far interior locations.

&&

.SHORT TERM...
Issued at 1155 AM PDT Sun Aug 3 2025
(This afternoon through Monday night)

The last vestiges of marine stratus continues to gradually erode as
of the noontime hour across the Monterey Bay region. On the synoptic
scale, the broad 500mb trough axis will shift east of our area
with 12 hour mid-level heights trending toward neutral. What this
translates to is additional light compression of the marine
layer. Monday morning should feature less in the way of cloud
cover with a smaller areal coverage of fog/drizzle. Areas along
the coast, as well as valleys with easy access to bodies of water
will have the greatest potential for clouds, fog, and even patchy
drizzle. Outside of these locales, optimal radiational cooling
may allow for the temperatures to tumble down into the mid 40s
(assuming winds subside prior to peak cooling). Most areas,
however, will experience MinTs tonight into Monday morning in the
50s and 60s.

Winds are still anticipated to increase, though the peak magnitude
is a little less certain compared to 24 hours ago. For now, the
forecast/messaging will hold serve. VWP from the Bodega Bay and Fort
Ord profilers indicate that 0-1 km flow is around 20 to 25 knots
which is a little lower than what was anticipated, though this does
appear to be captured by the 12 UTC NWP. This in tandem with some
supplemental/probabilistic tools such as the Extreme Forecast Index
(EFI) support elevated winds across the marine environment, along
the coast, and through the gaps, channels, passes, and valleys.
Traditional deterministic guidance continues to advertise a ramp up
of winds through tonight with 925mb flow ranging from 35 to 45 knots
across the coastal waters and adjacent land areas. Some of this
flow will be redirected through the various channels and gaps
across the East Bay and Southern Salinas Valley. Coastal jets are
also anticipated to develop downwind of Point Arena and Point Sur
where winds will result in rough conditions.

Winds are anticipated to ramp up around 1pm - 2pm today and peak
later this evening between 10pm and 1 am Monday. Peak gusts of up0
to 45mph (though I wouldn`t doubt a 50mph gust at Altamont
Pass/other channels in the East Bay). Winds abate through the day
on Monday as the gradient between the Central Valley thermal
trough and relatively higher pressure offshore eases. Elevated
wind gusts of 20 to 35 mph are still anticipated along the coast,
however. Daytime highs will remain below early August standards,
though with perhaps a compressed marine layer, temperatures may
overachieve in some spots.

&&

.LONG TERM...
Issued at 1155 AM PDT Sun Aug 3 2025
(Tuesday through next Saturday)

The overall theme for the extended forecast remains on track with a
gradual warm up through the end of the week. Beyond that, there`s a
little more agreement that at least our persistent upper
troughing will become more diffuse. A majority of the low-
resolution grand ensemble members in the 8 to 10 day range
indicate that ridging may take shape across the eastern Gulf of
Alaska promoting more in the way of troughing across the Great
Basin. This pairs well with some of the longer range predictions
that advertise a medium/moderate risk for extreme heat largely
across the Central Valley. While a little early to say exactly how
things will unfold for the Bay Area and Central Coast,
probabilities for above normal high temperatures between days 8
and 14 are above 50%.

For the remainder of the work week, however, we still anticipate
pockets of moderate HeatRisk, though the areal coverage has
diminished some since the last forecast update. The current
forecast resides largely with the deterministic NBM as it`s about
a 50/50 split in terms of ensemble member groupings offering a
warmer than or cooler than the grand ensemble temperature
forecast. Just to recap, if the magnitude of troughing remains
more persistent than currently thought, the deterministic NBM has
a better chance of verifying, with the messaging of a warm
up/pockets of moderate HeatRisk being appropriate. However, if the
troughing really diminishes and/or the Four Corners high moves
farther to the west, then subsidence warming and/or weakly
offshore flow will promote warmer than NBM temperatures. This may
manifest itself in potentially a greater coverage of moderate
HeatRisk as well. As it stands right now, there doesn`t seem to be
much support to advertise any sort of major heatwave for our
area, though we will continue to monitor as temperatures approach
+5 to +10 degrees above climatological norms.

Just as a reminder, the eastern Pacific remains quite active
with tropical activity. Climatologically, these have been an
important player for some of our fires induced by lightning events
in August. At this time, the train of tropical cyclones appears
that it`ll remain far south enough such that there will be little
to no influence. We`ll need to watch the position of the coastal
trough, Four Corners high and subsequent mid/upper level moisture
feeds.

&&

.AVIATION...
(06Z TAFS)
Issued at 931 PM PDT Sun Aug 3 2025

The clear skies now look to have more staying power through the
night, particularly for the northern terminals. According to
GFSLAMP probabilistic guidance, there is a 25% chance for IFR
ceilings to develop in the North Bay, 20% chance at SFO and OAK,
and a 60% chance at MRY and SNS. HREF guidance is similar with the
exception of the North Bay where the probability is surprisingly near
zero. Otherwise the clear skies will help strong winds mix down to
the surface tomorrow afternoon, with similar impacts expected as
we saw today.

Vicinity of SFO...The chance for ceilings overnight has more or
less held steady, and I removed mention in the TAF. That said,
there is still a chance as stratus is expected to bank up along
the Pacific coast of the Peninsula and the strong NW winds could
bring ceilings through the San Bruno gap. If ceilings do form,
the duration should be much shorter than normal. Otherwise the
main focus is on another round of strong winds in the afternoon,
with SFO likely reaching gusts of 35 kts or more from the West.

SFO Bridge Approach...Better chance to stay clear compared to SFO.

Monterey Bay Terminals...While the satellite and observations are
currently clear, ceilings are still expected to develop over MRY
and SNS early Monday morning. That said, they should clear a few
hours after sunrise due to the warmer and dryer air mass that has
clearly infiltrated the boundary layer to some extent. The onshore
winds won`t be as strong as the Bay Area, but gusts to 20 kts are
still possible at SNS Monday afternoon.

&&

.MARINE...
(Tonight through next Saturday)
Issued at 931 PM PDT Sun Aug 3 2025

Strong to near gale force northwesterly winds will continue
through Monday before improving slightly. Winds are locally
stronger along the coast north of Point Reyes and South of Point
Sur with frequent gale force gusts being observed. Seas will
remain moderate to rough through the week.

&&

.FIRE WEATHER...
Issued at 1155 AM PDT Sun Aug 3 2025

The fire weather threat will elevate this afternoon. Fires are
likely to be limited to the grass/brush fuel types and for a few
hours this afternoon, there could be some sites that flirt with or
briefly exceed our RFW matrix/criteria. The period with peak
winds should coincide with an increase in RH, though portions of
the East Bay Hills and lower elevations of the Santa Lucia Range
will likely see RH between 20 and 30 percent as the winds ramp up
this afternoon. Overnight RH recovery will remain poorest across
the higher reaches of the Santa Lucia Range, Santa Cruz Mountains,
Gabilan Range, and Eastern Santa Clara/East Bay Hills with values
between 20% and 40%. Elsewhere, RH should rebound above 50%. As
our subtle warming trend peaks later this week, with above normal
warmth returning in the days 8 to 14 range, we`ll see the fire
weather threat elevate again. Of particular note will be energy
release components approaching the 90th percentile for the Mid-
Coast to Mendocino predictive service area (North Bay) later this
week.

&&

.MTR WATCHES/WARNINGS/ADVISORIES...
CA...None.
PZ...Small Craft Advisory until 3 AM PDT Monday for Mry Bay-Pigeon Pt
     to Pt Pinos 0-10 nm-SF Bay N of Bay Bridge.

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

     Gale Warning until 3 AM PDT Monday for Pt Arena to Pt Reyes 0-10
     nm-Pt Pinos to Pt Piedras Blancas 0-10 nm.

     Small Craft Advisory until 9 PM PDT Monday for Pt Reyes to
     Pigeon Pt 0-10 nm.

     Small Craft Advisory until 9 AM PDT Tuesday for Pigeon Pt to Pt
     Pinos 10-60 NM-Pt Arena to Pt Reyes 10-60 NM.

&&

$$

SHORT TERM...Bain
LONG TERM....Bain
AVIATION...Flynn
MARINE...Flynn

Visit us at www.weather.gov/sanfrancisco

Follow us on Facebook, X, and YouTube at:
www.facebook.com/nwsbayarea
x.com/nwsbayarea
www.youtube.com/nwsbayarea