FXUS66 KMTR 261130
AFDMTR

Area Forecast Discussion
National Weather Service San Francisco CA
430 AM PDT Wed Aug 26 2026

...New AVIATION, MARINE...

.KEY MESSAGES...
Updated at 1209 AM PDT Wed Aug 26 2026

 - Temperatures near to slightly below seasonal averages persist
   within the shallow marine layer through Thursday

 - Seasonably warm and very dry conditions continue above 1000
   feet and the far interior through Thursday

 - Pattern change Friday into the weekend brings cooler
   temperatures and moderate potential for tropical moisture

&&

.SHORT TERM...
Issued at 1209 AM PDT Wed Aug 26 2026
(Today and tonight)

Stratus clouds are developing at the immediate coast and will expand 
into the coastal valleys through the night, before mixing out 
Wednesday morning. The weather pattern today remains dominated by 
the balance between ridging in the Desert Southwest and troughing in 
the eastern Pacific, with a slight edge to the ridging as reflected 
in a general warming trend across the region. Highs in the inland 
valleys reach the middle 80s to the middle 90s, up to 106 within the 
warmest regions of southern Monterey County, with the Bays reaching 
the middle 70s to the middle 80s and the Pacific coast remaining 
rather cool in the lower to middle 60s. A gentle to moderate onshore 
breeze develops in the afternoon and evening hours with gusts of 20 
to 30 mph at the coast, through gaps and passes, and within the 
Salinas Valley. The marine layer will remain around 1000-1500 ft 
today, with warm and dry conditions above the marine layer 
inversion. See the FIRE WEATHER section for the implications for 
local fire weather concerns.

&&

.LONG TERM...
Issued at 1209 AM PDT Wed Aug 26 2026
(Thursday through Tuesday)

The ridging remains in place through Thursday with temperature 
around the same as today's before the trough over the eastern 
Pacific begins to migrate eastwards late Thursday into Friday, 
starting a cooling trend that will last through the early part of 
next week. As the trough moves into the West Coast, it will pull in 
tropical moisture partially from what would be the remnants of 
Tropical Storm Iselle and direct it towards the state. The model 
trend for steadily increasing Precipitable Water values has 
continued to play out, with ensemble model probabilities suggesting 
that Oakland is likely to see precipitable water values exceeding 
1.0 inches on Friday morning. For context, the 90th percentile value 
for precipitable water at OAK is 1.04 inches, and pretty much all 
the deterministic models that go out this far have OAK exceeding 
this value, with some of the wetter models making a run for or 
exceeding the daily maximum value, which for the 12Z (5 AM PDT) 
soundings on August 28, would be 1.24 inches. This kind of setup 
would definitely bring high clouds to the region and also brings the 
risk of high-based rain showers and thunderstorms to the region. One 
of the big caveats of this risk, especially as it pertains to 
thunderstorms, is that model output also suggests that instability 
is lacking with the European model showing virtually no CAPE 
anywhere within the atmosphere, surface or elevated. We will 
continue to monitor the evolution of this setup closely. 

The incoming trough will also lead to an tightening of the pressure 
gradient, which in turn will lead to breezier winds Friday into the 
weekend. Gusts will rise to 25 to 35 mph along the coast and through 
favored gaps, valleys, and passes. The troughing pattern will 
continue to develop into the early part of next week, when 
temperatures will dip 5 to 15 degrees below the seasonal average, 
with highs in the 70s to lower 80s in the interior valleys. The
current forecast has some rain chances returning towards the
middle of next week, but this is critically dependent on the
future evolution of the situation in the tropical East Pacific,
and as a result the confidence in this forecast is very low at
this time.

&&

.AVIATION...
(12Z TAFS)
Issued at 419 AM PDT Wed Aug 26 2026

The mid/high clouds moved out of our area and the marine layer
quickly reorganized and made a push inland. IFR/LIFR has developed
for a majority of the terminals with KLVK likely to be the only
site impacted by stratus ceilings through the remainder of the
forecast period.

Vicinity of SFO...A steady fetch of onshore flow channeling
through the Bay Area was interrupted briefly by high clouds 
earlier Tuesday night into this morning but has now begun to 
increase in coverage. VFR ceilings are expected by mid-morning as 
stratus retreats back toward the coastline.

SFO Bridge Approach...Similar to SFO.

Monterey Bay Terminals...IFR/LIFR ceilings developed in the wake 
of upper level clouds, after is seemed possible stratus might not 
fill in. Coverage is still not as extensive as normally seen at 
this time, with VFR expected by mid to late morning. IFR/LIFR 
ceilings aren't expected to return until around sunset.

&&

.MARINE...
(Today through Monday)
Issued at 419 AM PDT Wed Aug 26 2026

Fresh to strong northwest winds will continue today into the
weekend with moderate wind driven seas. A long period southerly
swell will build late in the week becoming 17-18 seconds by Friday
and persist through at least early Sunday.

&&

.FIRE WEATHER...
Issued at 1209 AM PDT Wed Aug 26 2026

Not much has changed in terms of the fire weather threat, with near 
critical fire weather conditions persisting in the higher elevations 
above 1000 feet through Thursday due to warm and dry conditions. 
Overnight humidity recoveries remain poor to very poor within these 
areas and the impact of the marine layer inversion leads to 
temperatures warmer than the seasonal average, especially within the 
Santa Lucia range and the interior Central Coast where temperature 
are running as much as 15 to 20 degrees above the seasonal 
average. Model output suggests that an offshore flow has set up 
over the Big Sur coast at the 925 mb level, supporting the risk 
for overnight nocturnal drying in the interior Central Coast and 
particularly surrounding the Timber Fire. Last night I had noted 
that the southwest winds seemed to bring in more moist air into 
the Santa Lucia range, and that the overnight diminishing of winds
when combined with the offshore push led to an unusual situation 
where the maximum daily relative humidities took place during the 
day. This remains the case, up until the ridgeline parallel to the
Big Sur coast when the southwest winds begin to downslope and dry
the region. Unfortunately there aren't a lot of weather station 
in these areas to verify the conceptual model. Smoke transport 
from the Timber Fire will continue to peak in the afternoon and 
evening with the plume spreading towards the Salinas area. Friday 
into the weekend, a pattern change should allow for some relief as
an upper level trough comes into the region bringing cooler 
temperatures and a deeper marine layer.

DialH

&&

.MTR WATCHES/WARNINGS/ADVISORIES...
CA...None.
PZ...Small Craft Advisory until 9 AM PDT Friday for Pigeon Pt to Pt 
     Pinos 0-10 nm-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.

&&

$$

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

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Prepared by Boulder-Creek.com Weather at: Wed Aug 26 10:30:03 PDT 2026