FXUS66 KMTR 231806
AFDMTR

Area Forecast Discussion
National Weather Service San Francisco CA
1106 AM PDT Wed Sep 23 2026

...New UPDATE...

.KEY MESSAGES...
Updated at 1103 AM PDT Wed Sep 23 2026

 - Warming trend continues into Thursday bringing pockets of
   moderate HeatRisk across parts of the Bay Area and Central
   Coast.

 - Cooler conditions arrive Friday into the weekend.

 - Near seasonal temperatures early next week.

&&

.UPDATE...
Issued at 1103 AM PDT Wed Sep 23 2026

The OAK 12Z sounding measured the marine layer around 1400 feet deep 
this morning, which is roughly 1000 feet shallower compared to 
yesterday's sounding. This morning, poor humidity recoveries around 
20-30% were observed across the Diablo Range, Santa Cruz Mountains, 
and the Santa Lucia range. Another round of poor humidity recoveries 
is expected through tomorrow morning. A very weak push of offshore 
flow will persist through the overnight hours as high pressure 
continues to build over us, further compressing the marine layer 
tonight into Thursday morning. While current temperatures are 
running about 4-6 degrees below the forecast, they are still 
expected to rise this afternoon as stratus continues to dissipate. 
Consequently, pockets of moderate HeatRisk will impact the interior 
East/South Bay and Central Coast valleys as well as the Big Sur 
coastline into tomorrow. Come early Friday morning, a dry cold 
frontal passage with a strong onshore push will allow the marine 
layer to deepen and provide relief with cooler conditions through 
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...
(18Z TAFS)
Issued at 1055 AM PDT Wed Sep 23 2026

Mostly VFR currently, the exception is KHAF where LIFR conditions
persist. VFR is expected by late morning and will persist until 
late this evening when sub-MVFR conditions return to the coastal 
areas. There confidence is moderate for coastal locations to 
receive sub- IFR and lower confidence for the Bay Area Terminals 
early Thursday morning. Any low clouds or fog that does develop 
will clear between 1630Z-1730Z Thursday.

Vicinity of SFO...VFR. Onshore winds are forecast to increase 
this afternoon, yet no significant gusts expected. Wind speeds 
ease overnight and into early Thursday morning with a low 
confidence for sub-MVFR (10-30% probability) yet MVFR is more 
likely with 20-50% probability at or around 11Z Thursday. Any low 
clouds that does develop will clear between 1630Z-1730Z Thursday 
with increasing onshore winds by Thursday afternoon. 

SFO Bridge Approach...Similar to SFO. 

Monterey Bay Terminals...VFR. Onshore winds are forecast to 
increase this afternoon before easing after sunset. There is 
moderate confidence to see similar conditions late this evening 
and into the overnight as we saw this morning. There is moderate 
confidence for sub-IFR (30-50% probability) late tonight into 
Thursday morning before returning to VFR by around 17Z Thursday. 

&&

.MARINE...
(Today through Monday)
Issued at 1055 AM PDT Wed Sep 23 2026

Northerly breezes will 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.

&&

.MTR WATCHES/WARNINGS/ADVISORIES...
CA...None.
PZ...Small Craft Advisory until 3 AM PDT Thursday for Pt Arena to Pt 
     Reyes 10-60 NM.

&&

$$

SHORT TERM...RW
LONG TERM....RW
AVIATION...RGass
MARINE...RGass

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Prepared by Boulder-Creek.com Weather at: Wed Sep 23 14:30:03 PDT 2026