FXUS66 KMTR 112340
AFDMTR
Area Forecast Discussion
National Weather Service San Francisco CA
440 PM PDT Tue Aug 11 2026
...New AVIATION, MARINE...
.KEY MESSAGES...
Updated at 1209 PM PDT Tue Aug 11 2026
- Low confidence for elevated showers and thunderstorms Wednesday
afternoon through Thursday morning across the Central Coast
- Cooling trend continuing into Thursday, bringing temperatures
below seasonal averages with gradual warming Friday into the
weekend
- Minor coastal flooding at high tide for bayshore locations
along the San Francisco Bay, San Pablo Bay, and Monterey Bay
through Thursday morning
&&
.SHORT TERM...
Issued at 1209 PM PDT Tue Aug 11 2026
(This evening through Thursday morning)
Stratus clouds linger along the immediate coast through the day,
before coming into the inland valleys overnight into Wednesday
morning. Smoke from the Timber Fire south of Big Sur continues to be
transported northwards into the Monterey Bay region due to
southwesterly transport winds, and this is expected to continue
through the next couple of days. For air quality forecasts, refer to
products issued by the Monterey Bay Air Resources District within
the Central Coast, and the Bay Area Air Quality Management District
within the San Francisco Bay Area.
The weather pattern is dominated by a developing upper level trough
that will continue a cooling and moistening trend through the next
couple of days. Today's high temperatures range from the 80s and
lower 90s in the inland valleys, up to the middle 90s in the warmest
interior spots, the 70s and lower 80s along the Bays, and the lower
to middle 60s along the Pacific Coast. Lows tonight into Wednesday
morning range from the 50s and lower 60s within the lower
elevations, up to the middle 60s to lower 70s above the marine layer
influence at around 2000 feet. Overnight drizzle is possible along
the coast and within favored upslope foothill areas through the
Petaluma Gap and within the East Bay.
For Wednesday, attention turns to an upper level low that is
currently meandering around 300 miles southwest of Point Conception,
where space- and ground-based observations have pointed to some
lightning occuring within a high-based thunderstorm cell. Through
the next couple of days, that cell will start to move along a
moisture gradient, which could locally enhance the lapse rates, into
the Central Coast, with around a 10-15% probability of high-based
showers and thunderstorm activity across Monterey and San Benito
Counties between Wednesday afternoon and the early part of Thursday
morning. Primary threats are gusty outflow winds and the potential
for dry lightning and its attendant fire weather implications; see
the FIRE WEATHER section for more details. Main question right now
is if the cell will hold together as it approaches the coast. Water
vapor imagery is showing a layer of drier air within the cell's
path, which could disrupt the system as it approaches California.
Elsewhere, the general cooling trend continues as highs reach the
upper 70s to middle 80s inland, the upper 60s to the middle 70s near
the Bays and the lower to middle 60s along the Pacific coast.
As a final note, minor coastal flooding is possible across the low
lying bayshore areas of the San Francisco, San Pablo, and Monterey
Bays at the highest high tide through Wednesday night/Thursday
morning. At the San Francisco tidal gauge, high tide is expected to
be 1.6 ft above normal (7.44 ft MLLW) at 10:57 PM Tuesday 8/11 and
1.4 ft above normal (7.24 ft MLLW) at 11:49 PM Wednesday 8/12. High
tides may result in flooding along coastal trails, cut off access to
some low-lying coastal areas and beaches, and bring water and waves
farther up the beach than typical. If travel is required, allow
extra time as some roads may be closed. Do not drive, bike, or walk
around barricades or through water of unknown depth.
&&
.LONG TERM...
Issued at 1209 PM PDT Tue Aug 11 2026
(Thursday afternoon through next Monday)
The cooling trend continues through Thursday with highs in the
inland valleys dropping into the 70s, or around 10 to 20 degrees
below the seasonal averages, possibly as high as the middle 80s in
the warmest spots, and highs into the 60s close to the Bays.
Beginning on Friday, the trough begins to flatten out, allowing for
gradual warming to occur, although temperatures will remain below
seasonal averages given that the troughing pattern never really goes
away, it just merges with another trough coming in from the eastern
Pacific and lurks just offshore for the weekend before migrating
back over the West Coast for the early part of next week, when highs
will be in the middle 70s to lower 80s inland and the middle 60s to
lower 70s near the Bays.
&&
.AVIATION...
(00Z TAFS)
Issued at 428 PM PDT Tue Aug 11 2026
VFR prevails across the area with the marine layer lingering along
the coastline. The gradual increase in depth of the marine layer
is underway and is expected to reach ~2000ft later tonight through
the middle of the week at least. However, active offshore eddys
continue to complicate the progression inland and impacts over the
Bay Area. Despite being surrounded overnight and early this
morning KSFO still didn't register a ceiling. So even if not being
reported directly at the terminal be prepared for low ceilings in
vicinity of terminals near the coast.
Vicinity of SFO...VFR is expected to prevail at KSFO through the
forecast period, however expect MVFR/IFR ceilings on approach
after sunset through Wednesday morning. KOAK is expected to
develop MVFR/IFR ceilings around/soon after midnight, earlier than
previous couple nights as the marine layer depth continues to
gradually increase.
SFO Bridge Approach...MVFR/IFR ceilings likely on approach even
if not reported at KSFO.
Monterey Bay Terminals...Once again, more typical diurnal pattern
of MVFR/IFR ceiling development for this time of year than points
north. MVFR/IFR ceilings expected prior to sunset and continuing
through the middle to late morning Wednesday, returning around the
same time Wednesday early evening.
&&
.MARINE...
(Tonight through next Sunday)
Issued at 428 PM PDT Tue Aug 11 2026
Fresh to strong northwest winds persist into Thursday with
occasional near gale force gusts possible tonight across the
northern outer waters. Wind driven rough seas continue to build up
to 12 feet across areas with strong breezes. A long period
southerly swell gradually increases to 17 to 19 seconds by the
end of the week. Visibility impacts due to haze and smoke is
possible across the coastal waters due to an active fire on the
Big Sur coastline.
&&
.FIRE WEATHER...
Issued at 1209 PM PDT Tue Aug 11 2026
Near-critical fire weather conditions are forecast for Monterey and
San Benito counties as a low pressure system currently around 300
miles southeast of Point Conception moves onshore Wednesday
afternoon through Thursday early morning. Observations from space-
and ground-based instruments suggest that a high-based convective
cell within that low pressure system is producing lightning. If the
cell holds together, that could bring a chance of lightning-induced
fire starts to the region, especially within higher elevation areas
that have continued to see poor to very poor overnight humidity
recoveries. Examples include the Santa Lucia range, adjacent areas
of Los Padres National Forest, and the Gabilan range within interior
Monterey and San Benito counties. Given the high-based nature of the
thunderstorms, there may be little to no rainfall associated with
the cells, raising the prospects for dry lightning. In addition,
gusty and erratic outflow winds could promote fire growth for
ongoing fires and new starts near a thunderstorm complex. The main
source of uncertainty lies in the behavior of the system as it moves
closer to shore, potentially into a dry slot in the upper levels,
that could impact how the cell develops as it moves onshore. This is
currently a low confidence, high impact scenario, especially given
ongoing fire activity with the Timber Fire and intense tourist
activity within the Monterey Bay region. If confidence in
thunderstorm impacts increases through the night, a Red Flag Warning
may need to be issued. Beyond the passage of the cells, fire weather
conditions should improve as a deepening ridge causes the marine
layer to deepen and overnight humidity recoveries to increase to
relative humidity values of 40% and above within the higher
elevations.
DialH
&&
.MTR WATCHES/WARNINGS/ADVISORIES...
CA...Coastal Flood Advisory until 2 AM PDT Thursday for CAZ006-506-
508-529-530.
PZ...Small Craft Advisory until 9 AM PDT Thursday for Pt Arena to Pt
Reyes 10-60 NM.
&&
$$
SHORT TERM...DialH
LONG TERM....DialH
AVIATION...JM
MARINE...Navarrete
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Prepared by Boulder-Creek.com Weather at: Tue Aug 11 18:30:03 PDT 2026
From the National Weather Service
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