Technical NOAA Weather Discussion

FXUS66 KMTR 211826
AFDMTR

Area Forecast Discussion
National Weather Service San Francisco CA
1126 AM PDT Fri Aug 21 2026

...New AVIATION, MARINE...

.KEY MESSAGES...
Updated at 1017 PM PDT Thu Aug 20 2026

 - Temperatures will be close to or below normal into the
   beginning of next week

 - Warm and dry conditions above 1000ft persist into the weekend

&&

.SHORT TERM...
Issued at 1017 PM PDT Thu Aug 20 2026
(Friday and Friday night)

Improved onshore flow in the lower boundary layer especially for the 
North Bay and Bay Area should result in more extensive stratus 
intrusion overnight coinciding with overnight lows closer to normal 
for this time of year. Warm and dry conditions will continue both 
overnight and through the day above 1000ft inland and near the 
coast, this includes in vicinity of the Timber Fire where relatively 
light winds continue to be a mitigating factor. Some elevated 
convection earlier Thursday night has tapered off or now in the 
steering flow of the ridge. Any mid/upper level moisture attempting 
to reach the Central Coast would be greeted by anemic instability 
and confluent flow aloft.

As the closed portion of the upper level low responsible for the 
persistent troughing recently will slowly approach the Oregon coast 
later tonight with a steady fetch of onshore flow continuing across 
our area, with only a marginal increase in depth of the marine layer 
expected into early Saturday morning.

&&

.LONG TERM...
Issued at 1017 PM PDT Thu Aug 20 2026
(Saturday through next Thursday)

The parent low mentioned above moves onshore into the PacNwest 
during the day Saturday with a weak troughing pattern lingering 
offshore at our latitude through at least the weekend. However, the 
persistent ridging over the Desert Southwest will shift east as well 
during this time , thus we'll continue to see the cooling trend 
through the weekend into the beginning of next week. There's a weak 
signal for the ridging to the east to build back toward the west 
coast by the middle of next week, which would bring warmer 
temperatures, but at that point a potential tropical system well to 
our southwest may add noise to the NWP.

&&

.AVIATION...
(18Z TAFS)
Issued at 1125 AM PDT Fri Aug 21 2026

Currently have a mix of IFR to VFR ceilings due to patchy stratus 
across our region. VFR conditions are expected to prevail this 
afternoon into the early evening hours. HAF is an exception as they 
may have a couple hours of VFR scattered cloud decks in the early 
afternoon before shifting back to IFR ceilings. Moderate to fresh 
onshore breezes around 10 to 15 kt expected through the day and ease 
overnight. The marine layer returns this evening impacting coastal 
sites first before filling in over inland terminals. Low to medium 
confidence on the exact stratus arrival as it is dependent on where 
the upper level low sets up during the day. Currently, all TAF sites 
are expected to develop IFR to MVFR ceilings, with coastal sites 
having a high chance of dropping to LIFR in the overnight hours.

Vicinity of SFO...Stratus is beginning to mix out of the SF Bay as 
moderate onshore breezes increase. VFR through the afternoon with 
occasional gusts around 20-25 kt possible. Winds remain around 10 kt 
overnight. Medium confidence on the timing of IFR ceilings as they 
may arrive as early as sunset. The marine stratus is expected to 
linger until late Saturday morning.

SFO Bridge Approach...Ceilings that develop may not be as low as SFO 
and clear before SFO does. Otherwise, similar to SFO.

Monterey Bay Terminals...Stratus is receding to the coastline 
resulting in VFR conditions through the afternoon. Onshore winds 
will be diurnally driven this TAF period. The marine layer holds on 
strong as it returns with IFR ceilings this evening around 6-7 PM 
PDT. Medium confidence that ceilings will drop to LIFR overnight 
(OVC003-004), but there is still uncertainty regarding the exact 
timing and duration of LIFR conditions. If LIFR ceilings develop, 
they are likely to impact visibility and linger at the terminals 
through mid Saturday morning.

&&

.MARINE...
(Today through Wednesday)
Issued at 1125 AM PDT Fri Aug 21 2026

An upper level low pressure system situated off the west coast is
resulting in moderate to fresh northwest breezes across the outer
waters. Strong breezes with occasional near gale force gusts in
the coastal jet regions of Point Reyes and Point Sur is expected.
Widespread hazardous conditions to small crafts across the coastal
and bay waters continue into Saturday with diurnal sea breezes.
Wind driven seas remain slight to moderate through the weekend.

&&

.MTR WATCHES/WARNINGS/ADVISORIES...
CA...None.
PZ...Small Craft Advisory from 3 PM this afternoon to 9 PM PDT this 
     evening for Mry Bay-SF Bay N of Bay Bridge.

     Small Craft Advisory until 3 AM PDT Saturday for Pigeon Pt to Pt 
     Pinos 0-10 nm-Pt Arena to Pt Reyes 0-10 nm-Pt Pinos to Pt 
     Piedras Blancas 0-10 nm-Pt Reyes to Pigeon Pt 0-10 nm.

     Small Craft Advisory from 3 PM this afternoon to 3 AM PDT 
     Saturday for Pigeon Pt to Pt Pinos 10-60 NM-Pt Arena to Pt 
     Reyes 10-60 NM.

&&

$$

SHORT TERM...JM
LONG TERM....JM
AVIATION...Navarrete
MARINE...Navarrete

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Prepared by Boulder-Creek.com Weather at: Fri Aug 21 14:30:02 PDT 2026
From the National Weather Service