FXUS66 KMTR 231211
AFDMTR

Area Forecast Discussion
National Weather Service San Francisco CA
511 AM PDT Wed Sep 23 2026

...New AVIATION, MARINE, FIRE WEATHER...

.KEY MESSAGES...
Updated at 1232 PM PDT Tue Sep 22 2026

 - Warming trend continues through Thursday

 - Cooler conditions Friday into the weekend

&&

.SHORT TERM...
Issued at 1103 PM PDT Tue Sep 22 2026 (Tonight through Thursday)

Marine layer between 1500-2000 feet deep as of Tuesday evening.
Low clouds cover areas from Point Reyes southward to Big Sur with
a decent push of stratus in SF Bay and the Monterey Bay region
including Salinas valley. There is an increasing northerly
gradient now to about 5 mb from ACV-SFO that is eroding the 
stratus from north to south for the North Bay. This is occurring 
as high pressure is trying to nose into the region from the 
southwest. 850 mb temps warming to around 20-21 celsius with hot 
inland temps for the interior Central Coast (90s) with mainly 
upper 80s to around 90 for the interior North/South/East Bays on 
Weds afternoon. With persistent onshore winds not really a late 
September setup where we would expect warm/hot temps at the coast.
Looking at the European extreme forecast index we see no areas of
interest suggesting this is just a typical warm late Sept day on 
tap. Models hold onto the warm inland temps for one more day 
through Thursday. However by Thursday afternoon a storm well to 
our north will induce a strong onshore/westerly push, ushering in 
a moderate to strong afternoon/evening seabreeze on Thursday that 
will signal relief for the Bay Area while the interior Central 
Coast remains warm/hot through Thursday evening.

&&

.LONG TERM...
Issued at 1103 PM PDT Tue Sep 22 2026 (Thursday night through 
next Tuesday)

A fairly well defined early autumn dry cold front passage will push
through the region Thursday night into Friday morning. No precip 
is forecast for the Bay Area as it remains confined to areas north
of Cape Mendocino. However, enough cooling and mixing aloft to 
essentially erode or mix out the marine layer quickly by early Friday
morning. Temps still remain seasonably warm/mild Friday but the 
cooling trend will have begun. Weather this weekend looks nice for
the last weekend of September. Certainly no hot weather with 
inland temps mainly 70s to lower 80s Saturday/Sunday with enough 
cold air aloft and mixing to keep skies sunny with perhaps only 
some patchy morning low clouds near the coast and bays. 

Early look at next week shows no signal for precip or abnormally
hot weather and no fall offshore wind events. Pattern looks pretty
zonal suggesting temps running near seasonal norms. 

&&

.AVIATION...
(12Z TAFS)
Issued at 445 AM PDT Wed Sep 23 2026

Marine layer returned, but a tad more compressed this morning in
the 1500-1800 foot range. As such, seeing more reduced vis with
LIFR conditions for N Bay and Monterey Bay regions. Elsewhere IFR
for SF Bay and VFR for S and E Bays. Expecting VFR this afternoon
as N-S increases. Less CIGs expected tonight with drier airmass
and strong pressure gradients, but conf is low for CIGs SF Bay.

Vicinity of SFO...Circulation inside SF Bay led to some clearing
earlier in the night, but since then eddy weakened and stratus
filled in for SFO with IFR CIGs. Will keep CIGs into the AM rush
then VFR this afternoon. Low conf for CIGs tonight, but did
include some CIGs late tonight.

SFO Bridge Approach...Similar to SFO.

Monterey Bay Terminals...LIFR conditions will impact Monterey Bay
areas through mid-late morning. VFR expected this afternoon. IFR
to LIFR conditions return early this evening.

&&

.MARINE...
(Today through Monday)
Issued at 445 AM PDT Wed Sep 23 2026

Northerly breezes will ease early Wednesday near shore, but remain
moderate to fresh over the outer waters. Locally hazardous
conditions will persist for small craft over the outer waters
through Wednesday night. Winds will weaken further across all
waters on Thursday. Friday will see an increase in northwest
winds accompanied by seas building back up to rough, and
continuing into the weekend.

&&


.FIRE WEATHER...
Issued at 440 AM PDT Wed Sep 23 2026

Marine layer returned again impacting lower portions of the
district this morning with excellent RH recovery. Similar to
yesterday morning patchy fog will impact the N Bay Valleys, 
Monterey Peninsula and the Salinas Valley. Unlike yesterday two
other notable differences: the exact footprint of the marine 
layer is slightly different with less coverage over the E Bay
Valleys and along the Big Sur coastline and moderate to poor
recoveries above the marine layer. Speaking of the drier 
conditions aloft, RH recoveries are 15 to 50 pct drier depending 
on locations. In other words, nocturnal drying returned. 
Otherwise, warmer and drier across the board, especially interior 
locations.

MM

.MTR WATCHES/WARNINGS/ADVISORIES...
CA...None.
PZ...Small Craft Advisory until 5 AM PDT early this morning for 
     Pigeon Pt to Pt Pinos 10-60 NM-Pt Arena to Pt Reyes 0-10 nm.

     Small Craft Advisory until 3 AM PDT Thursday for Pt Arena to Pt 
     Reyes 10-60 NM.

&&

$$

SHORT TERM...RW
LONG TERM....RW
AVIATION...MM
MARINE...MM

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Prepared by Boulder-Creek.com Weather at: Wed Sep 23 08:30:03 PDT 2026