FXUS66 KMTR 260713
AFDMTR
Area Forecast Discussion
National Weather Service San Francisco CA
1213 AM PDT Wed Aug 26 2026
...New SHORT TERM, LONG TERM, FIRE WEATHER...
.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...
(06Z TAFS)
Issued at 1100 PM PDT Tue Aug 25 2026
VFR prevails with the exception of KSFO and KHAF with stratus
coverage not nearly as extensive as expected. 00z KOAK balloon
measured a relatively weak marine layer around 1000ft similar to the
Bodega Bay profiler. Guidance is struggling with the current
conditions leading to a low confidence forecast through Wednesday
morning.
Vicinity of SFO...KSFO is currently IFR, have decided to maintain
that until approximately 15z. As mentioned above, this is a low
confidence forecast with guidance struggling wrt stratus pushing
inland overnight. Low level boundary layer flow channeling into
the Bay Area should provide some coverage through mid-morning with
KOAK expected to see IFR ceilings around or shortly after
midnight tonight, and lift with similar timing as KSFO.
SFO Bridge Approach...Similar to SFO.
Monterey Bay Terminals...Difficult forecast with current guidance
not picking up on the current clear skies. Unlike the North Bay
and Bay Area, there is actually a weak fetch of offshore flow
through the overnight. That combined with some mid/high level
cloud cover limiting radiational cloud top cooling, may remain
VFR through the TAF period. For now have a chance of IFR ceilings
developing around sunrise with peak radiational cooling potential
and less mid/high level cloud cover expected. If ceilings
eventually develop after sunset, they should lift by mid-morning.
&&
.MARINE...
(Tonight through next Monday)
Issued at 836 PM PDT Tue Aug 25 2026
Moderate northwest breezes with strong gusts continue tonight as
moderate wind driven seas prevail through the week. Northwest
winds become fresh to strong Wednesday into the weekend. A long
period southerly swell approaches our coastal waters by the end of
the week.
&&
.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 Thursday 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...DialH
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Prepared by Boulder-Creek.com Weather at: Wed Aug 26 04:30:03 PDT 2026
From the National Weather Service
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