Technical NOAA Weather Discussion

FXUS66 KMTR 220702
AFDMTR

Area Forecast Discussion
National Weather Service San Francisco CA
1202 AM PDT Tue Sep 22 2026

...New SHORT TERM, LONG TERM...

.KEY MESSAGES...
Updated at 1201 AM PDT Tue Sep 22 2026

 - Warming trend begins today through Thursday

 - Cooler conditions Friday into the weekend

&&

.SHORT TERM...
Issued at 1201 AM PDT Tue Sep 22 2026
(Today and tonight)

Extensive stratus has flowed into the North Bay valleys, Monterey 
Bay region, Salinas Valley, Hollister area, and the East Bay west of 
the Berkeley Hills. Across the rest of the SF Bay Area, patches of 
stratus have developed near Livermore and north of San Jose, with 
further expansion expected through the pre-dawn hours. The cloud 
deck retreats back to the immediate coast late this morning into the 
early afternoon, but by the time it develops again tonight, the 
marine layer will be compressed, leading to uncertainty over just 
how far inland the clouds will go. 

The cut-off low that gave us the last couple days of cooler 
temperatures is moving across the state with the center crawling 
through the Mojave Desert into the Great Basin. This allows for more 
zonal flow to come into the state and a warming trend to begin 
today, with high temperatures in the upper 70s to the middle 80s 
across the inland valleys, into the upper 80s in the far interior 
regions of the North Bay and southern Monterey County, the middle 
60s to the middle 70s close to the Bays, and the lower to middle 60s 
along the immediate coast. A breezy onshore wind will develop in the 
afternoon and evening hours, with the strongest gusts of 20 to 30 
miles per hour along the coast, through favored gaps and passes, and 
within the northern Salinas Valley.

As a quick side note, today will mark the autumnal equinox and the 
start of astronomical fall. At 505 PM Pacific time, the sun's 
apparent path on the Earth crosses the equator, giving us 12 hours 
each of sunlight and nighttime.

&&

.LONG TERM...
Issued at 1201 AM PDT Tue Sep 22 2026
(Wednesday through Monday)

Slight ridging will develop over California over the next couple of 
days, and while the ridge axis quickly moves into the Intermountain 
West, the ridge influence will allow for further warming Wednesday 
and Thursday. High temperatures warm into the middle 80s to the 
middle 90s in the inland valleys, the middle 70s to the middle 80s 
close to the Bays, and the middle 60s to the lower 70s along the 
Pacific Coast. Pockets of Moderate HeatRisk are scattered across the 
interior regions, particularly near San Jose, the interior East Bay, 
and the Santa Lucia range. These pockets are not expansive enough to 
merit a Heat Advisory. 

By Friday, a developing trough in the eastern Pacific comes into the 
West Coast, and a cooling trend will cause temperatures to dip near 
and below seasonal averages. Weekend highs range from the middle 70s 
to the middle 80s in the inland valleys and the middle 60s to the 
middle 70s close to the Bays. Temperatures will recover early next 
week as the trough flattens and ensemble model cluster analysis 
hints at a ridge developing somewhere within the western United 
States, although the exact impacts are not certain at this point.

&&

.AVIATION...
(06Z TAFS)
Issued at 1021 PM PDT Mon Sep 21 2026

Extensive MVFR-IFR stratus has flowed into the North Bay and the 
Monterey Bay region, and continues to develop in the SF Bay region. 
A deep marine layer should allow many of the inland valleys to see 
ceilings overnight before the stratus retreats back to the immediate 
coast late Tuesday morning. Low to moderate confidence in temporary 
scatterings at HAF and MRY around the 19-22Z timeframe. Gentle to 
moderate onshore winds will develop Tuesday afternoon and evening. 
Stratus forecasts for Tuesday night into Wednesday morning are lower 
confidence, particularly away from the immediate coast, as a 
compressing marine layer should keep stratus away from many inland 
regions but lower ceilings and visibilities where it does form.

Vicinity of SFO... A tricky forecast for the next several hours as 
the stratus feed through the Golden Gate gets deflected to the 
north, leaving the terminal area VFR. High resolution model output 
has the terminal getting MVFR ceilings imminently, but the models 
have not captured the current situation well and have kept the 
terminal VFR for the time being. If stratus forms over SFO expect 
the clouds to scatter out late Tuesday morning, with a moderate west 
breeze developing in the afternoon and evening hours. Low confidence 
of stratus returning Tuesday night, which most of the high 
resolution guidance has backed away from and may be impacted by a 
compressing marine layer.

SFO Bridge Approach... MVFR stratus may arrive before or after it 
gets to the terminal tonight, depending on how exactly the stratus 
develops with SF Bay. Otherwise similar to SFO.

Monterey Bay Terminals... MVFR ceilings at present with IFR 
conditions expected later tonight. Stratus will scatter out Tuesday 
late morning to the early afternoon, with moderate confidence in a 
brief scattering period at MRY near 19-22Z. Stratus is expected to 
return to MRY late in the afternoon and persist into the evening. At 
SNS, confidence is lower as the compressing marine layer may keep 
the deck away, but on the flip side, the compression could also 
lower ceilings and visibilities at MRY on Tuesday night.

&&

.MARINE...
(Tonight through next Sunday)
Issued at 826 PM PDT Mon Sep 21 2026

Moderate to fresh northwest breezes persist overnight with
locally stronger winds north of Point Reyes. By Tuesday afternoon,
widespread strong northwest winds prevail across the coastal
waters, allowing for seas to build from moderate to rough.
Northwest winds and seas remain elevated through the week with a
brief period of improved conditions Wednesday night into Thursday.
By Friday, winds increase with building rough seas.

&&

.FIRE WEATHER...
Issued at 423 AM PDT Mon Sep 21 2026

An upper-level low will support near to slightly below normal 
temperatures, increased diurnal winds, a deep (2,500') marine 
layer. Warming and drying trend kicks off Tuesday with 
temperatures up to 10 degrees above normal and areas of moderate 
HeatRisk Wednesday and Thursday. The marine layer will compress 
below 1,000 feet during this warm-up with nocturnal drying 
expected above it.

&&

.MTR WATCHES/WARNINGS/ADVISORIES...
CA...None.
PZ...Small Craft Advisory until 5 AM PDT Wednesday for Pt Arena to Pt 
     Reyes 0-10 nm-Pt Arena to Pt Reyes 10-60 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 from 3 PM this afternoon to 3 AM PDT 
     Wednesday for Pt Pinos to Pt Piedras Blancas 0-10 nm.

     Small Craft Advisory from 3 PM this afternoon to 5 AM PDT 
     Wednesday for Pigeon Pt to Pt Pinos 10-60 NM.

&&

$$

SHORT TERM...DialH
LONG TERM....DialH
AVIATION...DialH
MARINE...DialH

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Prepared by Boulder-Creek.com Weather at: Tue Sep 22 04:30:03 PDT 2026
From the National Weather Service