FXUS66 KMTR 280954
AFDMTR
Area Forecast Discussion
National Weather Service San Francisco CA
254 AM PDT Mon Sep 28 2026
...New MARINE...
.KEY MESSAGES...
Updated at 1240 AM PDT Mon Sep 28 2026
- Elevated fire weather conditions across the higher terrain
through Wednesday
- Areas of moderate HeatRisk across the interior Wednesday
through Sunday
- Minor coastal flooding for bayshore locations along the San
Francisco, San Pablo, and Monterey Bays Monday through Friday
&&
.SHORT TERM...
Issued at 1240 AM PDT Mon Sep 28 2026
(Monday through Tuesday)
An upper-level low will dig diagonally across the state Monday into
Tuesday. Sensible weather wise, Monday will be the coolest day of
the week with temperatures near to slightly below normal alongside
onshore winds of 10-20 mph with gusts up to 30 mph. All signs point
to the 2,000 ft marine layer mixing out, yet it prevails. The
associated lift and accompanying wind from the aforementioned low
will favor an earlier than normal clearing time of stratus (although
it's more like stratocumulus out there). Of more impact is the
northerly/offshore flow that will develop as upper-level ridging
noses in from the Eastern Pacific Ocean in the low's wake. Wind
speeds of 15-25 mph with gusts up to 35 mph can be expected across
the interior higher terrain, especially the North Bay Interior
Mountains and East Bay Interior Mountains. This will start tonight
(Sunday night/Monday morning) and peak Monday night/Tuesday morning
and Tuesday night/Wednesday morning. The combination of dry and
windy conditions will yield elevated fire weather conditions for the
higher terrain during this time. Tuesday and Wednesday will be
warmer and drier from rising heights and northerly (drying) winds.
Northerly/offshore flow will also minimize if not erode the marine
layer, allowing the coast to warmup. Minor coastal flooding for
bayshore locations along the San Francisco Bay, San Pablo Bay, and
Monterey Bay during the highest high tide Monday through Thursday.
&&
.LONG TERM...
Issued at 1240 AM PDT Mon Sep 28 2026
(Wednesday through Sunday)
Global ensemble clusters are in agreement that upper-level ridging
with anomalously high heights will dictate our forecast Wednesday
through Sunday. 850 mb temperatures above the 90th percentile will
support temperatures 10 to 15 degrees above normal. As a result,
areas of moderate HeatRisk are expected across the interior above
and away from the compressed (<~1,000 ft) marine layer. No daily
maximum temperature records are in jeopardy.
&&
.AVIATION...
(06Z TAFS)
Issued at 910 PM PDT Sun Sep 27 2026
VFR/MVFR conditions continue across our terminals. Developing
offshore flow should hold off stratus/fog developing for the North
Bay. Plenty of uncertainty of the drier air filling in behind the
upper trough currently shifting east across our area. Where
stratus develops near the coastal terminals, there's a slight
chance of patchy fog and drizzle.
Vicinity of SFO...MVFR ceilings have persisted all afternoon and
evening. Not much clarity in guidance, thus a low confidence
forecast that MVFR ceilings will mix out late in the overnight
hours as drier air fills in behind the upper trough mentioned
above.
SFO Bridge Approach...Similar to SFO.
Monterey Bay Terminals...Steady onshore flow continues to produce
low level stratus/stratocu with no end in sight based on satellite
trends. Drier air will take more time to filter that far south,
with more diffuse effects thus maintaining more typical clearing
to VFR by mid/late Monday morning.
&&
.MARINE...
(Today through Saturday)
Issued at 252 AM PDT Mon Sep 28 2026
Moderate to strong north winds will continue through Wednesday
with the strongest gusts across the northern outer waters and
south of Point Pinos, where near gale force gusts are expected at
times. Rough seas will build in response to these winds and will
subside to moderate by the end of the week due to northerly winds
becoming light to moderate. Tropical activity will produce long
period swell up to 16 seconds Wednesday and Thursday.
&&
.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...Coastal Flood Advisory from 11 AM this morning to 5 PM PDT
Thursday for CAZ006-506-508-529-530.
PZ...Small Craft Advisory from 3 PM this afternoon to 3 AM PDT
Wednesday for Pt Arena to Pt Reyes 0-10 nm.
Small Craft Advisory from 3 PM this afternoon to 9 PM PDT this
evening for Pigeon Pt to Pt Pinos 0-10 nm.
Small Craft Advisory until 11 PM PDT this evening for Pt Pinos
to Pt Piedras Blancas 0-10 nm.
Small Craft Advisory until 3 PM PDT Wednesday for Pigeon Pt to
Pt Pinos 10-60 NM-Pt Arena to Pt Reyes 10-60 NM.
&&
$$
SHORT TERM...Sarment
LONG TERM....Sarment
AVIATION...JM
MARINE...KR
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Prepared by Boulder-Creek.com Weather at: Mon Sep 28 04:30:03 PDT 2026
From the National Weather Service
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