FXUS66 KMTR 280021
AFDMTR
Area Forecast Discussion
National Weather Service San Francisco CA
521 PM PDT Sun Sep 27 2026
...New AVIATION, MARINE...
.KEY MESSAGES...
Updated at 1214 PM PDT Sun Sep 27 2026
- Cool conditions today
- Warming trend for the rest of the week
&&
.SHORT TERM...
Issued at 1214 PM PDT Sun Sep 27 2026
(This evening through Monday night)
High clouds continue to float over the Bay Area and Central Coast,
while stratus coverage lingers across coastal Marin and San Mateo
counties, the Oakland area, the city of San Francisco, and the
southern Monterey Bay region. Some mixing out is possible through
the afternoon where the high clouds clear out, but some coastal
regions may remain socked in through the day. Stratus should return
inland this evening and overnight.
Water vapor imagery shows a deep trough, perhaps even a cut-off low,
centered just off of Cape Mendocino, which brings in cooler air to
the region. Highs today will range in the 70s for the inland
valleys, into the lower to middle 80s for the warmest spots of
southern Monterey County, and the upper 50s to the lower 70s for the
coastal and Bayshore regions. Breezy onshore winds will develop in
the afternoon and evening with gusts of 20 to 30 mph at the coast,
through favored gaps and passes, and within the Salinas Valley.
As the trough/low moves across the state, and ridging comes in
behind it, the upper level winds over the Bay Area and Central Coast
will shift from southwesterly to northeasterly, leading to a push of
offshore flow on Monday morning. The strongest winds look to develop
on the lee sides (southwest-facing slopes) of the interior mountains
of the North Bay, where hydraulic jump effects will push wind gusts
to around 20 mph. High temperatures will warm a fair bit in the
inland valleys, where the forecast calls for middle 70s to middle
80s, and the Bayside locations, which should expect highs in the
upper 60s to middle 70s.
&&
.LONG TERM...
Issued at 1214 PM PDT Sun Sep 27 2026
(Tuesday through next Saturday)
Additional pushes of higher elevation offshore flow will set up on
Tuesday morning and Wednesday morning, chiefly across the North and
East Bay interior mountains. The strongest push looks to be on
Tuesday morning with wind gusts of 25 to 35 mph possible in the
interior mountains of the North Bay. The potential for wind gusts
above 35 mph is greatest at the ridgeline of the Vaca Mountains
along the eastern border of Napa County.
Otherwise, seasonably warm temperatures should be fully
established by Tuesday as highs in the inland valleys reach the
middle 80s to the middle 90s, those in the Bayshore regions reach
the middle 70s to the middle 80s, and the Pacific coast reaches
the middle 60s to middle 70s. Temperatures may fluctuate by a few
degrees each day but the general trend should remain similar
through the end of the seven day outlook. Some areas of Moderate
HeatRisk, a level of heat that brings a moderate risk of heat-
related illnesses to sensitive populations, will develop through
the next few days, but confidence in widespread impacts is not
high enough to issue a Heat Advisory at this point. Longer-range
guidance suggests that temperatures above the seasonal average
will continue into the middle of October.
As a final point, minor coastal flooding is possible in low-lying
areas across the San Francisco, San Pablo, and Monterey Bay
shorelines Tuesday through Thursday. Up to 1.1 feet of inundation
above normally dry land is expected, including up to 0.6 ft of
surge caused by thermal expansion and sea level rise since the sea
level datum (basically the point where we define as "sea level")
was set in the 1983-2011 period. At the San Francisco tidal gauge,
high tide is expected to be 1.0 ft above normal (6.81 ft MLLW) at
1:30 PM Tuesday 9/29, 1.1 ft above normal (6.93 ft MLLW) at 2:10
PM Wednesday 9/30, and 1.0 ft above normal (6.82 ft MLLW) at 2:58
PM on Thursday 10/1.
&&
.AVIATION...
(00Z TAFS)
Issued at 445 PM PDT Sun Sep 27 2026
A mix of VFR/MVFR despite limited extent of stratus coverage
currently. Guidance is mixed on coverage of potential stratus
overnight and early Monday morning. A surge of dry air is
complicating the forecast even with a marine layer measured at
2000ft by the KOAK 00z balloon launch.
Vicinity of SFO...MVFR ceilings have been steady this afternoon
with a marine layer of 2000ft. Drier air is expected to shift
south from the North Bay during the overnight along with a weak
fetch of offshore flow, with VFR expected for the remainder of the
forecast period.
SFO Bridge Approach...Similar to SFO.
Monterey Bay Terminals...Despite limited coverage mentioned
above, onshore flow continues to drive stratus development along
the Monterey Peninsula impacting KMRY and KSNS with MVFR ceilings
that are expected to hold through Monday morning, however there
may be some periods of VFR for the remainder of this evening.
&&
.MARINE...
(Tonight through next Friday)
Issued at 445 PM PDT Sun Sep 27 2026
Moderate north winds will persist today, becoming moderate to
strong as we head into Monday. Strongest winds will be over
northern outer water and south of Point Pinos with near gale force
gusts expected at times. Winds hold through midweek then taper
becoming light to moderate by the end of the work week. Tropical
activity will produce long period southerly swell by the middle of
the week.
&&
.FIRE WEATHER...
Issued at 1214 PM PDT Sun Sep 27 2026
Today is the last day of seasonally cool and moist conditions before
warmer and drier air comes in for the next week, especially above
the marine layer inversion. Upper level northeasterly flow will
combine with hydraulic jump effects in the lee side of the mountains
to create some breezy offshore gusts each morning from Monday
through Wednesday. The strongest winds are expected on Tuesday
morning in the interior mountains of the North and East Bays, where
wind gusts could reach 30 mph. These offshore winds should
contribute to poor overnight humidity recoveries, with overnight
relative humidities as low as 20-40% above the marine layer, and a
chance for nocturnal drying events across the higher elevations.
DialH
&&
.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-Pt Arena to Pt Reyes 0-10 nm.
Small Craft Advisory until 11 PM PDT Monday for Pt Pinos to Pt
Piedras Blancas 0-10 nm.
Small Craft Advisory until 3 PM PDT Wednesday for Pt Arena to Pt
Reyes 10-60 NM.
Small Craft Advisory from 9 PM this evening to 3 PM PDT
Wednesday for Pigeon Pt to Pt Pinos 10-60 NM.
&&
$$
SHORT TERM...DialH
LONG TERM....DialH
AVIATION...JM
MARINE...CW
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Prepared by Boulder-Creek.com Weather at: Sun Sep 27 20:30:03 PDT 2026
From the National Weather Service
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