FXUS66 KMTR 201137
AFDMTR
Area Forecast Discussion
National Weather Service San Francisco CA
437 AM PDT Thu Aug 20 2026
...New AVIATION, MARINE...
.KEY MESSAGES...
Updated at 1147 PM PDT Wed Aug 19 2026
- Gradual cooling trend today into the beginning of the weekend
- Elevations above about 1000 feet will have warm temperatures
and RH values in the teens early this morning into the
afternoon
&&
.SHORT TERM...
Issued at 1147 PM PDT Wed Aug 19 2026
(Today and tonight)
We've been in the middle of a subtle back and forth between
troughing over the EPAC and ridging over the desert southwest the
past week or so. The net result has been only small changes in our
day-to-day ambient weather conditions. However, the influence of
troughing nudging back to the east toward our coastline today, will
result in the beginning of gradual cooling, that will continue into
the weekend. Improved lower boundary layer onshore flow will help
bring temperatures around 5-10 degrees below normal away from the
coast, while still remaining above normal in southern Monterey
County. The depth of the marine layer influence will increase as
well today helping to further support cooler temperatures. The more
mild overnights we've been seeing will moderate closer to normal
too, leading to stratus pushing farther inland after sunset into
early Friday morning.
&&
.LONG TERM...
Issued at 1147 PM PDT Wed Aug 19 2026
(Friday through Wednesday)
The gradual cooling trend into the beginning of the weekend levels
off by Sunday into the beginning of next week with only minor,
likely unnoticeable changes through the remainder of the extended
forecast. The strong dome of high pressure over the desert
southwest shows hints of shifting back to the west by the end of
next week, which would bring warmer temperatures, however there is
still no signal for a significant pattern change. Tropical wave
activity is still expected to steer well south and west of our
area with little to no impacts on our forecast attm.
&&
.AVIATION...
(12Z TAFS)
Issued at 430 AM PDT Thu Aug 20 2026
Mix of VFR to LIFR conditions this morning as the marine layer
starts to compress. LIFR-IFR conditions will improve by late
morning with VFR conditions this afternoon and evening. Moderate
confidence on timing of stratus return tonight with IFR-LIFR CIGs
likely. Low confidence that stratus will reach LVK tonight, most
likely a tempo will be needed for stratus again after 12Z
tomorrow. Breezy onshore winds expected this afternoon with the
SFO-WMC gradient peaking around +8 mb.
Vicinity of SFO...IFR CIGs have been eddying in and out of SFO
over the last few hours with eddy activity expected to continue.
Patchy IFR ceilings will continue impacting SFO through approx.
16Z but as late as 18Z. Breezy onshore winds return this afternoon
and evening with gusts peaking around 25 knots. Moderate
confidence in timing of stratus return tonight with IFR ceilings
expected.
SFO Bridge Approach...An eddy has developed within the SF Bay
region that is pulling clouds away from the SFO terminal but
leaving some on the Bridge Approach path. Ceilings are most likely
IFR to MVFR and will clear by late morning. Otherwise, similar to
SFO.
Monterey Bay Terminals...LIFR-IFR ceilings continuing through late
this morning with VFR conditions briefly returning this afternoon
and evening. Stratus returns during the early evening hours with
ceilings on the IFR-LIFR border. Ceilings will lower overnight
with worsening visibilities towards the end of the TAF period.
&&
.MARINE...
(Today through Tuesday)
Issued at 430 AM PDT Thu Aug 20 2026
A moderate to fresh northwesterly breeze prevails through Friday.
Hazardous conditions for small craft due to occasional strong
northwest gusts continue across the outer waters and coastal jet
regions into Friday. Moderate seas continue across the outer
waters with wave heights increasing to between 7 to 8 feet before
decreasing Friday into the weekend.
&&
.MTR WATCHES/WARNINGS/ADVISORIES...
CA...None.
PZ...Small Craft Advisory until 3 AM PDT Friday 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 until 3 PM PDT Friday for Pt Pinos to Pt
Piedras Blancas 0-10 nm.
&&
$$
SHORT TERM...JM
LONG TERM....JM
AVIATION...Kennedy
MARINE...Kennedy
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Prepared by Boulder-Creek.com Weather at: Thu Aug 20 10:30:02 PDT 2026
From the National Weather Service
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