FXUS66 KMTR 171625
AFDMTR
Area Forecast Discussion
National Weather Service San Francisco CA
925 AM PDT Mon Aug 17 2026
...New UPDATE, MARINE...
.KEY MESSAGES...
Updated at 1201 AM PDT Mon Aug 17 2026
- Shallower marine layer through midweek
- Minor fluctuations in temperatures this week
&&
.UPDATE...
Issued at 925 AM PDT Mon Aug 17 2026
Water vapor imagery shows an elongated upper level trough off the
West Coast this morning, with a disturbance moving through this
trough off the Mendocino Coast. This disturbance is bringing
plenty of mid and upper level cloud cover to Northern and Central
California. Given this thick cloud shield, it is hard to see the
inland extent of the marine layer. However, we are continuing to
see ceilings at all of our terminals, except for Livermore, which
is scattered at this time. In addition, the 12z KOAK sounding
shows that is it still shows the marine layer at 1800 feet deep,
and we once again saw some patchy drizzle along the immediate
coast, with several locations, mainly around the Monterey
Peninsula and Bay, measuring 0.01 inches.
Given this blanket of high clouds, most locations were not as
cool this morning as yesterday, and for that reason, we are
running 2 to 4 degrees warmer than this time yesterday. However,
this cloud cover is also going to limit our day time heating.
Therefore, expect another day of below normal to near normal
temperatures across the region. Currently forecast seems to be
handling these trends well, so no update is planned at this time.
Palmer
&&
.SHORT TERM...
Issued at 1201 AM PDT Mon Aug 17 2026
(Today and tonight)
Quiet weather today with little to no impactful weather expected
through the next week. Temperatures today will be near or slightly
below normal for this time of year with slightly more mild overnight
lows to wake up to this morning than we've seen the last few days
due to mid/high level cloud cover insulating radiative cooling. The
mid to high level cloud cover will continue out ahead of a
persistent troughing pattern over the EPAC. The additional cloud
cover may impact daytime highs as well, limiting peak day heating
somewhat. Some patchy fog and drizzle may be possible as well,
especially right along the coastline.
&&
.LONG TERM...
Issued at 1201 AM PDT Mon Aug 17 2026
(Tuesday through Sunday)
Slight shifting in the persistent troughing over the EPAC and the
upper level ridging over the Four Corners region will result in
subtle warming Tuesday and Wednesday, as the upper ridge pushes
west slightly. The troughing pushes back to the east for the
remainder of the week, cooling temperatures a few degrees.
Overall, temperatures will be on the cooler side of normal for a
majority of forecast period. There is no clear signal for a
significant pattern change through the extended forecast.
&&
.AVIATION...
(12Z TAFS)
Issued at 416 AM PDT Mon Aug 17 2026
High clouds and stratus are pushing into the Bay Area and Central
Coast this morning. Stratus coverage is less expansive today than
it has been over the previous two days with the marine layer
having compressed to approx. 1000 ft. This is bringing IFR
conditions to interior sites with LIFR conditions along the
coast. Coastal fog is possible with buoys supporting an upwards
transport of moisture offshore (a better environment for fog
development). Conditions improve by late morning with interior
sites to see VFR conditions this afternoon into the evening.
Coastal sites are a little trickier as stratus is forecast to hug
the shoreline through the day which may result in patchy stratus
intrusions at coastal sites during the afternoon. Kept HAF
overcast through the entire day but BKN/OVC ceilings may briefly
scatter out during the late morning/early afternoon. MRY and SNS
are more likely to clear out today but cloud cover is expected to
return during the early evening.
Vicinity of SFO...Stratus is visible on camera approaching SFO but
confidence is low as to the exact timing/duration of the stratus.
The current TAF has a tempo in through 16Z for patchy stratus but
this may need to be extended through 18Z (which ensembles suggest
as a reasonable late clearing time for today). Given that the
marine layer will be compressed again tonight, I pushed back the
timing for stratus return tonight to closer to 10Z. Confidence is
low to moderate on timing given that stratus is expected to be
patchy again tonight.
SFO Bridge Approach...Similar to SFO.
Monterey Bay Terminals...IFR-LIFR ceilings continue through late
morning before a brief period of VFR conditions returns this
afternoon. This is short lived with IFR-LIFR conditions returning
shortly after 00Z. Reductions in visibility become more likely
towards the end of the TAF period with a low potential for fog to
develop at both sites. Breezy onshore winds return during the
afternoon and evening before winds decrease overnight.
&&
.MARINE...
(Today through Saturday)
Issued at 925 AM PDT Mon Aug 17 2026
Winds gradually increase with a fresh to strong breeze developing
by late tonight and continuing through the end of the forecast
period. Locally stronger winds are possible in the coastal jet
regions north of Point Reyes and along the Big Sur coast. Seas
build to 7 to 9 feet by Tuesday and Wednesday before abating late
week.
&&
.FIRE WEATHER...
Issued at 1205 AM PDT Mon Aug 17 2026
Nocturnal drying through at least mid-week as the marine layer
gradually compresses. Expect more widespread fair to moderate
recoveries developing over the higher elevations, especially in
and around the Timber Fire.
&&
.MTR WATCHES/WARNINGS/ADVISORIES...
CA...None.
PZ...Small Craft Advisory from 3 AM to 3 PM PDT Tuesday for Pt Arena
to Pt Reyes 10-60 NM.
&&
$$
SHORT TERM...JM
LONG TERM....JM
AVIATION...Kennedy
MARINE...RGass
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Prepared by Boulder-Creek.com Weather at: Mon Aug 17 10:30:03 PDT 2026
From the National Weather Service
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