FXUS66 KMTR 241143
AFDMTR

Area Forecast Discussion
National Weather Service San Francisco CA
443 AM PDT Mon Aug 24 2026

...New AVIATION, MARINE...

.KEY MESSAGES...
Updated at 1200 AM PDT Mon Aug 24 2026

 - Temperatures near to slightly below seasonal averages persist
   within the marine layer through the rest of the week

 - Warm and dry conditions continue above 1000 feet

 - Pattern change Friday into the weekend brings cooler
   temperatures and possible tropical moisture

&&

.SHORT TERM...
Issued at 1200 AM PDT Mon Aug 24 2026
(Today and tonight)

For the last couple of days we've written the tale of a battle 
between the eastern Pacific trough and the Desert Southwest ridge 
that has dominated our weather pattern. Today it's the troughing 
that will take the upper hand as a cutoff low inches towards the 
Pacific Northwest, leading to slightly cooler temperatures and 
cloudier mornings across the region. Another interesting factor 
today is a weak shortwave trough coming into the region through the 
morning. The two main global weather models, the European ECMWF and 
the American GFS, are showing that there could be enough 
instability, moisture, and lift to maybe, just maybe, support a few 
high-based thunderstorms developing across the North Bay, 
particularly over Napa County. This is a very low probability 
forecast (around 5% chance through around 11 AM), along with a low 
confidence for storm development. The higher resolution NAM, HRRR, 
and RRFS models do not show any signs of developing storms, lapse 
rates aloft are marginal at best, and K-Index values below 20 
degrees Celsius suggest no chance for developing thunderstorms. Any 
precipitation that does develop is also likely to end up as virga, 
evaporating within the vast dry low layer where relative humidity 
values as of the 0Z (5 PM PDT) OAK sounding fell into the single 
digits.

Today's highs range from the 80s into the lower 90s for the inland 
valleys, the middle 90s to the triple digits across the warmest 
interior spots, the upper 60s to the upper 70s near the Bays, and 
the upper 50s to the middle 60s along the Pacific coast. The higher 
elevations above the marine layer influence will remain rather day, 
especially during the afternoon and evening hours. Breezy onshore 
pattern winds will develop this afternoon and evening with wind 
gusts reaching 20 to 30 mph along coastal jet regions, through 
favored gaps and passes, and within the northern Salinas Valley. 
Smoke from the Timber Fire will continue impacting the immediate 
area around the actively burning fire through the day, with winds 
aloft lofting the smoke plume over Salinas and Hollister. For air 
quality information, refer to products issued by the Monterey Bay 
Air Resources District.

&&

.LONG TERM...
Issued at 1200 AM PDT Mon Aug 24 2026
(Tuesday through Sunday)

Temperatures rebound Tuesday and Wednesday as the ridge reasserts 
itself, with the inland valleys reaching highs in the middle 80s to 
the middle 90s on Wednesday and Thursday while the Bays reach the 
lower 70s to the lower 80s. A pattern change will begin later on 
Thursday as a deep trough builds into the West Coast while the ridge 
begins to inch its way eastwards towards the Southern Plains. It 
will be interesting to see what the trough will do as the upcoming 
weekend comes closer and we are better able to refine the forecast. 
Also worth a mention is the possibility of tropical moisture coming 
into the region, with our colleagues at the National Hurricane 
Center tracking Tropical Storm Iselle and three other areas of 
interest off the coast of Mexico. While the circulations remain far 
to the south of our waters, the resultant moisture will be captured 
by the developing trough with a wide variation in just how far north 
the moisture goes. By way of example, the deterministic European 
ECMWF model brings a swath of tropical moisture into the San 
Francisco Bay Area by Friday morning, whereas the deterministic GFS 
keeps the moisture plume to the south of Monterey County. In 
addition, wave models are also showing an increase in southerly 
swells as the tropical eastern Pacific remains active into the early 
part of next week.

&&

.AVIATION...
(12Z TAFS)
Issued at 423 AM PDT Mon Aug 24 2026

Mixed bag of VFR/IFR/LIFR early this morning. Status filled north
into KSTS and is expected to lift by mid morning with VFR expected
to prevail across the Bay Area terminals and inland South Bay
airports. IFR/LIFR ceilings over Monterey Bay will give way to VFR
late morning, with IFR ceilings returning before sunset.

Vicinity of SFO...Low stratus lingers in vicinity of the terminals
but not expected to impact ceilings with VFR expected to prevail
throughout the day into the evening hours with MVFR/IFR expected 
to develop around midnight.

SFO Bridge Approach...Similar as SFO.

Monterey Bay Terminals...A relatively normal diurnal cycle of
IFR/LIFR ceilings expected through the forecast period, with
current IFR/LIFR ceilings expected to lift by late morning and
return in the early evening hours before sunset. Expect periods of
breezy onshore flow in the afternoon.

&&

.MARINE...
(Today through Saturday)
Issued at 423 AM PDT Mon Aug 24 2026

Gentle northwest breezes persist today into Tuesday with slight
to moderate wind driven seas. Smoke from the Timber Fire along the
Big Sur coast may limit visibility down as low as two miles at
times. North-northwest winds begin to increase by the middle of
the week, along with an increasing long period southerly swell by
the end of the week into next weekend.

&&

.MTR WATCHES/WARNINGS/ADVISORIES...
CA...None.
PZ...None.
&&

$$

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

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Prepared by Boulder-Creek.com Weather at: Mon Aug 24 10:30:03 PDT 2026