FXUS66 KMTR 270033
AFDMTR
Area Forecast Discussion
National Weather Service San Francisco CA
533 PM PDT Wed Aug 26 2026
...New AVIATION...
.KEY MESSAGES...
Updated at 140 PM 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 increased potential for tropical moisture
&&
.SHORT TERM...
Issued at 140 PM PDT Wed Aug 26 2026
(This evening through Thursday night)
Coastal stratus and fog retreated to the coast as of late morning
giving way to mostly sunny skies across the interior. Meanwhile,
smoke from the Timber Fire and newly developed Plaskett Fire
continue to move toward the northeast as 500 MB winds are
southwesterly. Today is forecast to be the warmest day of the week
with temperatures topping out in the upper 80s to mid 90s across
the interior and up to 107 within the warmest regions of southern
Monterey County. The shallow marine layer and continued onshore
winds will keep conditions cooler near the coast and across San
Francisco. A gentle to moderate onshore breeze develops in the
afternoon and evening hours with gusts of 20 to 35 mph at the
coast, through gaps and passes, and within the favored valleys.
Tonight, much less confidence in stratus and/or fog development
late in the evening and into Thursday morning as the region
remains between a trough of low pressure off of the Pacific
Northwest coast and high pressure over the Four Corners region.
Thursday, we are forecasting an increase in mid/upper level
moisture to advect northeastward across the region from the
remnants of Tropical Storm Iselle. Thus, have added a 15%
probability for rain showers across the Central Coast, South Bay,
and East Bay for Thursday afternoon. The probability of
thunderstorms remains extremely low, but cannot be ruled out as
there is some MUCAPE (instability aloft) forecast by several CAMs
and deterministic models. However, cannot rule out gusty and
erratic winds in and around any virga (rain not reaching the
surface), sprinkles, or light rain showers that are able to
develop. See the FIRE WEATHER section below for more information.
&&
.LONG TERM...
Issued at 140 PM PDT Wed Aug 26 2026
(Friday through next Tuesday)
PWAT values approach 1.25" and increase to greater than 1.50" by
Friday morning lending to a greater potential for wetting rains.
Have extended the 15% probability for rain showers to include the
Bay Area and North Bay from Friday morning through Friday
afternoon. However, widespread wetting rains (greater than 0.10")
is unlikely.
The approaching trough will also result in a cooling trend with
temperatures dropping to below seasonal averages. The increased
PWATs decrease as the aforementioned trough shifts inland by
Friday night and lower to around 0.50" by Saturday night. This
feature will also lead to a tightening pressure gradient which
would lead to breezier winds Friday and into the weekend. Gusts
are currently forecast to reach between 25 to 35 mph along the
coast and through favored gaps, valleys, and passes. Zonal flow
develops over the weekend holding temperatures steadily below
normal.
Another reinforcing trough develops off of the Pacific Northwest
coast by Monday, allowing afternoon temperatures to be some 10-20
degrees below seasonal averages. The current forecast has the
potential for rain showers returning towards the middle of next
week. However, this is heavily dependent on the evolution of
conditions over the tropical Eastern Pacific. Thus, confidence is
very low at this time.
&&
.AVIATION...
(00Z TAFS)
Issued at 533 PM PDT Wed Aug 26 2026
It's VFR across the forecast area except in the area of the Timber
Fire smoke and haze may reduce slant range and surface visibilities.
24 hour trends are mainly warmer and drier across the forecast area
and satellite imagery shows stratus and fog located mainly over the
outer CA coastal waters. The ACV-SFO pressure gradient strengthened
to 4.9 mb this afternoon, while the SFO-SAC pressure gradient is 2.4
mb. Coastal stratus and fog /IFR-LIFR/ redevelop tonight and Thursday
morning under a compressed marine layer. Coastal stratus and fog mix
out to VFR by late Thursday morning and afternoon.
Vicinity of SFO...VFR. West wind 20 to 28 knots until 04z then
easing to near 10 knots tonight and Thursday morning. West wind
increasing to 20 to 25 knots Thursday afternoon to mid evening.
SFO Bridge Approach...Similar to SFO.
Monterey Bay Terminals...VFR except tempo stratus and fog /IFR-LIFR/
11z-15z Thursday morning. Mid level clouds may result in a passing
high based shower Thursday afternoon.
&&
.MARINE...
(Tonight through next Monday)
Issued at 140 PM PDT Wed Aug 26 2026
Fresh to strong northwest winds will continue today into the
weekend with moderate wind driven seas. Occasional gale force
gusts in the outer and inner waters are expected through the
weekend. 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...RGass
LONG TERM....RGass
AVIATION...Canepa
MARINE...RGass
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Prepared by Boulder-Creek.com Weather at: Wed Aug 26 18:30:03 PDT 2026
From the National Weather Service
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