236
FXUS66 KMTR 041119
AFDMTR

Area Forecast Discussion
National Weather Service San Francisco CA
419 AM PDT Mon Aug 4 2025

...New SHORT TERM, LONG TERM, AVIATION, MARINE...

.KEY MESSAGES...
Updated at 322 AM PDT Mon Aug 4 2025

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

 - 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 322 AM PDT Mon Aug 4 2025
(Today and tonight)

Mostly clear skies this morning as drier air works in aloft. The
marine layer is still intact, just less noticeable due to the lack
of a cloud layer. The trough axis is still just to our west. Thus,
the surface low pressure is still in a good location to promote
robust onshore winds. In fact, to put some numbers to it, the
SFO-WMC gradient peaked around +6.2 mb today and is forecast to be
just as strong this afternoon. It won`t be widespread windy for
everyone equally, but if it was windy where you were yesterday,
you can reasonably expect the same today. Winds will taper off
this evening as the trough axis moves to our east and we re-enter
our "boring" pattern.

All in all, the greatest threat today will be the elevated grass
fire danger. See the FIRE WEATHER section below for more
information, but grasses and fine fuels are definitely ready to
burn. There was a fire start today off of I 580 between Hayward
and Dublin that quickly ate up some flashy fuels. It was put out
quickly thanks to a quick response, but it serves as a good
reminder as to what time of the year it is. Remember, one less
spark!

&&

.LONG TERM...
Issued at 322 AM PDT Mon Aug 4 2025
(Tuesday through Sunday)

Once again...the long term forecast remains largely unchanged. See
previous discussion.

PREV DISCUSSION...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...
(12Z TAFS)
Issued at 322 AM PDT Mon Aug 4 2025

Satellite imagery shows mostly clear skies across the region, with
patchy stratus lingering along the western coast of the San Mateo
Peninsula and the hills to the northeast of OAK and SNS. Confidence
in stratus extent is low through the TAF period with the high
resolution models tending to overdo the cloud coverage. The current
forecast generally carries the previously expected stratus extent
forward, but satellite monitoring will continue and MRY has a chance
of staying clear into the afternoon. Breezy northwest winds will
develop this afternoon and evening, diminishing overnight with some
stratus coverage returning as the winds become light.

Vicinity of SFO... Clear conditions continue into the daytime.
Breezy west winds gusting to 35 to 40 knots are expected this
afternoon and evening, diminishing overnight. Confidence in stratus
at the terminal tonight into Tuesday morning is low, with the
combination of high resolution models overdoing stratus extent
tonight and those same models showing the terminal at the edge of
the stratus deck both contributing to the forecast uncertainty.

SFO Bridge Approach... Similar to SFO.

Monterey Bay Terminals... Confidence has decreased in the earlier
stratus forecasts at the terminals, but a lingering patch of stratus
to the northeast of SNS is keeping a chance for cloud cover in the
TAFs. Have turned the ceilings into TEMPO groups for the rest of the
morning, noting that there is a chance that MRY remains clear
through the day. Breezy northwest winds will develop in the
afternoon, with stratus beginning to redevelop in the evening hours,
although confidence in the extent is low.

&&

.MARINE...
(Today through Saturday)
Issued at 322 AM PDT Mon Aug 4 2025

Strong to near gale force northwest winds will persist through
the day before slightly diminishing through Tuesday. Winds are
locally stronger along the coast north of Point Reyes, south of
Pigeon Point into Monterey Bay, and south of Point Sur with
occasional gale force gusts possible this afternoon and evening.
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 from 9 AM this morning to 9 PM PDT this
     evening for Mry Bay-Pigeon Pt to Pt Pinos 0-10 nm.

     Small Craft Advisory until 3 AM PDT Wednesday for Pigeon Pt to
     Pt Pinos 10-60 NM-Pt Arena to Pt Reyes 0-10 nm-Pt Arena to
     Pt Reyes 10-60 NM.

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

     Small Craft Advisory until 9 PM PDT Tuesday for Pt Pinos to Pt
     Piedras Blancas 0-10 nm.

&&

$$

SHORT TERM...Behringer
LONG TERM....Bain
AVIATION...DialH
MARINE...DialH

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