FXUS66 KMTR 140835
AFDMTR
Area Forecast Discussion
National Weather Service San Francisco CA
135 AM PDT Mon Sep 14 2026
...New SHORT TERM, LONG TERM...
.KEY MESSAGES...
Updated at 1240 AM PDT Mon Sep 14 2026
- Gustier, dry offshore winds across the Vaca Range and Altamont
Pass tonight into Monday
- Cooling trend through mid-week
&&
.SHORT TERM...
Issued at 1240 AM PDT Mon Sep 14 2026
(Today and tonight)
Longwave pattern over the West is heavily focused on the wound up
upper low sweeping through the N Rockies. Why is that important?
Behind this upper level feature surface high pressure is slowly
building across the Pac NW and into the Great Basin. Pattern
recognition in the fall-ish months leads to offshore flow
signals. As such, latest sfc pressure gradients from SFO-WMC
reveals a flip from onshore Sunday to trending offshore overnight.
While latest guidance has cut way back on offshore flow potential
from a few days ago to today, it is still offshore nonetheless.
The offshore gradient is projected to be -5ish mb, which is on
the lower end. Regardless current overnight observations show a
switch at Mt St Helena with gusts to 35 mph and lower RH. Not
expecting a big impact given the weakness off the offshore flow,
but will drive sensible weather with breezy, mild, and drier
conditions for N Mts and E Bay Hills through early Monday.
Elsewhere, mostly clear skies prevail overnight. The exceptions
are few high clouds passing overnight and some patchy stratus
along the coast/coastal waters from San Francisco Peninsula south
to Monterey Bay.
Speaking of pressure gradients, the N-S gradient has ramped up
while the W-E gradient has eased. As such, winds to will be less
than what was observed on Sunday. The stronger winds will shift
back over the coastal waters. That being said, still expecting
some breezy conditions for Monterey Bay, Pt Sur, and the Salinas
Valley. Temperatures today will rebound slightly with highs in
the 60s/70s coast and 80s to lower 90s inland...still a few
degrees below normal for mid-September.
Monday night - offshore flow eases as onshore flow returns. As
such, the marine layer will have a better shot at returning.
Latest guidance shows a better marine layer/stratus picture by
Tuesday morning with coastal clouds push locally inland into
Monterey Bay and Salinas Valley.
&&
.LONG TERM...
Issued at 140 AM PDT Mon Sep 14 2026
(Tuesday through Sunday)
Interesting longwave pattern develops heading into mid-week as
another upper low cuts off of the main flow aloft and drifts into
OR/NorCal. Overnight ensemble guidance shows the upper low is
pretty anomalously low for this time of year and packs a cold
punch too. Overall cooling trend is expected Tuesday through
Thursday. In fact, 850mb temps will drop down to 11 to 12 C, which
is an anomaly of -5 to -7. The record heat from last week will be
a distant memory as highs on Wednesday will be locked in the 60s
and 70s, with a few interior spots reaching into the mid 80s.
That's about 5 to 15 degrees below normal. The cold advection will
cause an uptick in winds too. Winds on Wednesday will be
strongest through the Delta, East Bay gaps/passes. The lower 500mb
heights and colder air will help to re-establish a more robust
marine layer Wednesday and Thursday with some guidance suggesting
drizzle along the coast. It does come with a price, nocturnal
drying above the marine layer may return over the highest peaks
Thursday morning.
Heading into next weekend the upper low fades and 500mb heights
rise and 850mb temps warm. Therefore the marine layer will begin
to compress and temperatures will trend back toward seasonable
levels.
&&
.AVIATION...
(06Z TAFS)
Issued at 926 PM PDT Sun Sep 13 2026
Currently VFR. MVFR stratus along the San Francisco Peninsula
Coast and Monterey Peninsula will impact HAF, MRY, and SNS at
least intermittently through mid-to-late morning. Otherwise, VFR
and diurnal winds will prevail.
Vicinity of SFO...Currently VFR with westerly flow. High
confidence on VFR and diurnal winds prevailing through the TAF
period.
SFO Bridge Approach...Similar to SFO.
Monterey Bay Terminals...Currently VFR and calm at MRY and VFR
with southwesterly flow at SNS. MVFR stratus has already impacted
MRY and is lingering within the vicinity of the terminals; as
such, expect at least intermittent MVFR ceilings through mid-to-
late morning. Diurnal winds will prevail.
&&
.MARINE...
(Tonight through next Saturday)
Issued at 926 PM PDT Sun Sep 13 2026
Hazardous conditions for small craft will continue for the coastal
waters and Monterey Bay through Monday. Conditions begin to
improve Tuesday as northwesterly breezes diminish with that trend
continuing through Thursday. Moderate to rough seas will prevail
through Tuesday before abating Wednesday.
&&
.FIRE WEATHER...
Issued at 422 AM PDT Sun Sep 13 2026
Patchy coastal stratus has developed overnight. 925 mb relative
humidities are higher over the Timber and Plaskett fires early
this morning. Tonight into Monday night, a light to gentle
offshore breeze (with occasionally moderate gusts) is forecast to
develop in the higher terrain as the mid/upper level trough axis
shifts into the northern Rockies. As such, areas above the marine
layer often experience nocturnal drying that will likely continue
through early this upcoming week.
&&
.MTR WATCHES/WARNINGS/ADVISORIES...
CA...None.
PZ...Small Craft Advisory from 3 PM this afternoon to 9 PM PDT this
evening for Mry Bay-Pigeon Pt to Pt Pinos 0-10 nm-Pt Reyes
to Pigeon Pt 0-10 nm.
Small Craft Advisory until 3 AM PDT Tuesday 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-Pt Pinos to Pt Piedras Blancas 0-10 nm.
Small Craft Advisory until 3 AM PDT early this morning for
Pigeon Pt to Pt Pinos 0-10 nm-Pt Reyes to Pigeon Pt 0-10 nm.
&&
$$
SHORT TERM...MM
LONG TERM....MM
AVIATION...Sarment
MARINE...Sarment
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Prepared by Boulder-Creek.com Weather at: Mon Sep 14 02:30:03 PDT 2026
From the National Weather Service
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