409
FXUS66 KMTR 131045
AFDMTR

Area Forecast Discussion
National Weather Service San Francisco CA
345 AM PDT Fri Jun 13 2025

...New SYNOPSIS, SHORT TERM, LONG TERM, FIRE WEATHER...

.SYNOPSIS...
Issued at 341 PM PDT Thu Jun 12 2025

Daily coastal stratus, breezy afternoon onshore winds, and
interior highs in the 70s to 80s and low 90s across the far
interior continue through this weekend. Dry conditions persist for
elevated terrain above the marine layer leading to some fire
concerns as grasses and smaller plants continue to cure.

&&

.SHORT TERM...
(Today and tonight)
Issued at 345 AM PDT Fri Jun 13 2025

A long wave trough will remain nearly stationary to the west of
the CONUS (approx 400 miles west of the Bay Area) in the vicinity
of 130W longitude today, tonight and through the weekend. Low
pressure development within the long wave trough will remain over
British Columbia/AK and part of the Pacific Northwest. Southward
over our forecast area with higher 500 mb heights, we are closer
to the 500 mb subtropical ridge currently centered over northern
Mexico. We`re about 1 week from the summer solstice. With a high
sun angle and stronger daily heat input, all of this is disruptive
for organized mid-latitude low pressure systems (and fronts) to
develop here this time of year. Though cool northwest winds
continue over the nearby coastal waters in contact with sea
surface temps 53F-57F undercutting lower to mid level thermal
ridging. Marine layer stratus continues to redevelop overnight.
Within and above the lower temperature inversion that makes up the
stable capping temperature inversion of the marine layer it is
dry and mild (upper 60s/lower 70s which is approx 75th percentile
at 2500 feet on long term Oakland upper air climatology) with
relative humidities varying from the teens to 30%. Below this
level humidities are greater to much greater. Fuel moistures are
lowest over the southern interior, however winds are for the most
part light across the southern interior.

With onshore winds prevailing today, highs (like Thursday) will
be mainly either at or below mid June 30 year normal highs today.
Expect highs in the upper 50s/60s immediate coast/coastside to the
70s/80s/90s, warmest to hottest farthest inland. Lows cooling to
the mid 40s to lower 50s tonight, except in the 60s at elevation
in the lower level temperature inversion.

&&

.LONG TERM...
(Saturday through Thursday)
Issued at 345 AM PDT Fri Jun 13 2025

Not much change is expected in the overall 500 mb and surface
weather pattern this weekend. The center of the subtropical ridge
will shift slightly eastward, still remaining located over
northern Mexico but also covering AZ/NM. 500 mb heights over our
forecast area will remain at or slightly above 580 decameters
within medium to broad scale and weak troughing. Northwesterly
winds continue at the surface with nightly/early morning stratus
redevelopment this weekend. On Monday a slightly downward
fluctuation in 500 mb heights will accompany a weak 500 mb trough
passage. On Tuesday the passage of the trough will then lead to an
increase in 500 mb heights influenced by the subtropical ridge to
our south stretching more west-east from the Eastern Pacific to
Mexico. By later in the week, 500 mb troughing will be mainly to
our north entering the Pacific Northwest with possible strengthening
of the surface high over the Eastern Pacific steepening the
northerly ACV-SFO pressure gradient and winds. Surface theta-e on
the ECMWF shows a reinforcement of cooler/drier air arriving from
the northwest Wednesday evening and night. This pattern may also
bump up daytime highs a few degrees above normal from mid to late
next week.

&&

.AVIATION...
(06Z TAFS)
Issued at 1002 PM PDT Thu Jun 12 2025

Currently a mixed bag of VFR-MVFR at the terminals. Widespread VFR
is expected by the afternoon with the exception of HAF. The pattern
continues to be largely unchanged, as such a very similar forecast
on tap. The marine layer is currently being observed at 1,500 feet
and compressing; as such, ceilings that do develop will be low-end
MVFR to high-end IFR. Low level wind shear is anticipated again
tonight and tomorrow night, particularly in the North Bay, as the
atmosphere decouples - generally expect light southwesterly winds at
the surface with strong northwesterly winds aloft.

Vicinity of SFO...Currently VFR with westerly flow. HREF and NBM
both tack a 60% probability of sub-VFR ceilings developing overnight
with high confidence in VFR by the afternoon. Westerly winds will
prevail through the TAF period with gusts up to 30 knots to be
expected.

SFO Bridge Approach...Clouds below FL040 will begin to filter in by
09Z, with moderate to high confidence in them dissipating by 17Z.

Monterey Bay Terminals...Currently MVFR with southwesterly flow at
MRY and VFR with northwesterly flow at SNS. SNS will deteriorate to
sub-VFR conditions shortly as stratus is being shown within the
vicinity of the terminal. VFR and westerly winds will prevail by
tomorrow afternoon.

&&

.MARINE...
(Tonight through next Wednesday)
Issued at 1002 PM PDT Thu Jun 12 2025

Fresh to strong northwesterly breezes, near gale force gusts,  and
moderate to rough seas will prevail through Monday. Expect gale
force gusts to develop near the coastal jet regions of Point Reyes
and Point Sur during the afternoon and evening hours.

&&

.FIRE WEATHER...
Issued at 322 AM PDT Fri Jun 13 2025

Higher elevation hill tops and mountain tops within the lower level
temperature inversion will more or less continue with mild/warm
temperatures and low humidities in the teens to 30%. There may be
fluctuations in temperature and humidity resulting in some improvement
in overnight recoveries depending on the depth of the marine layer
and strength of onshore winds over the weekend. Near the 2500 feet
elevation, humidity will remain approximately near the 10th percentile
for mid June. Elevated fire weather conditions in areas of dry fine
fuels, late day breezy to gusty winds and low humidity will continue
this weekend and next 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.

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

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

&&

$$

SHORT TERM...Canepa
LONG TERM....Canepa
AVIATION...Sarment
MARINE...Sarment

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