FXUS66 KMTR 172100
AFDMTR
Area Forecast Discussion
National Weather Service San Francisco CA
200 PM PDT Mon Aug 17 2026
...New SHORT TERM, LONG TERM, FIRE WEATHER...
.KEY MESSAGES...
Updated at 1201 AM PDT Mon Aug 17 2026
- Shallower marine layer through midweek
- Minor fluctuations in temperatures this week
&&
.SHORT TERM...
Issued at 200 PM PDT Mon Aug 17 2026
(This evening through Tuesday night)
Water vapor imagery continues to show an elongated upper level
trough off the West Coast this afternoon, with the parent low
centered near 32.5 North and 137.5 West. There are several
disturbances moving around this trough, including the one lifting
across southwest Oregon that brought all of the high cloud cover
to Central and Northern California today. Water vapor imagery also
shows high pressure over the Desert Southwest, with California
remaining between the two large scale features, with relatively
moist southwesterly flow aloft over us. Unfortunately, all of
moisture is in the upper atmosphere in the form of high clouds.
There has been enough breaks in these clouds though that
our daytime temperatures today are warming more than I initially
gave them credit for. In fact, most locations are running 3 to 6
degrees warmer today over yesterday. That is in part to the warmer
start to the day, but also the combination of increasing 850 mb
temperatures, a compressing marine layer, and then sunshine. The
question now is whether or not there will be enough clouds to be
another insulating blanket tonight? Looking at the IR imagery,
think this is a plausible solution, and expect mild conditions
once again tonight. The marine layer will return again tonight,
but should be shallower (around 1500 feet), and not be quite as
widespread as this morning.
The upper level ridge, despite being dirty, will be the dominate
weather feature for Tuesday and Tuesday night, helping to
continue to minor warming trend, especially across the inland
areas. Despite the minor warming trend, daytime temperatures will
remain near to below normal through for most areas, with just the
far inland areas being above normal. The marine layer will also
start to compress, with more patchy fog possible during the late
night and early morning hours. Palmer
&&
.LONG TERM...
Issued at 200 PM PDT Mon Aug 17 2026
(Wednesday through next Sunday)
This upper level ridge will remain our more dominate weather
feature at least Wednesday and potentially now into Thursday.
Therefore, expect inland areas to potentially see another degree
or two of warming on Wednesday, with little change for Thursday,
while coastal areas only see minor fluctuations, as a shallow
marine layer lingers along the coast.
The upper level low currently near 32.5 North and 137.5 West will
finally lift for Friday before moving into the Pacific Northwest
for the weekend. This will once again bring a deeper marine layer,
stronger onshore winds, and cooler conditions to the Bay Area and
Central Coast once again. That being said, the parent trough will
remain off the California Coast as another upper level low
replaces this first one. While the details are still not entire
clear on where this secondary parent low will set up, it will keep
California with south or southwesterly flow aloft through the
first part of next week. The East Pacific also looks to get active
with a series of easterly waves during this time. This could make
things a little more interesting around here, should something
try to form and slip north around the edge of the ridge. At this
point in time, that does not look likely, but can't fully rule it
out either. Needless to say, this is something that will bears
watching. For now though, expect continued dry through the period.
Palmer
&&
.AVIATION...
(18Z TAFS)
Issued at 1042 AM PDT Mon Aug 17 2026
Stratus is beginning to clear to the immediate coastline allowing
for VFR conditions across the interior. However, coastal terminals
may remain IFR/MVFR with only brief breaks in the low cloud cover
this afternoon. High level clouds will persist today as well.
Onshore winds increase this afternoon and remain gusty at times
through early evening. Expecting an inland push of stratus late this
evening and spreading into the inland valleys overnight. The
greatest potential for LIFR is in the coastal terminals and KSTS
early Tuesday morning. IFR/MVFR is most likely in the Bay Area
terminals early Tuesday morning before scattering out by 18Z-20Z
Tuesday. Onshore winds increase again by Tuesday afternoon.
Vicinity of SFO...VFR. Onshore winds are forecast to increase by
early this afternoon and will be gusty at times through early
evening. IFR/MVFR ceilings return early Tuesday morning with
weaker wind speeds, potentially variable at times Tuesday morning
before increasing once again by the afternoon.
SFO Bridge Approach...Similar to SFO.
Monterey Bay Terminals...LIFR at KMRY and MVFR at KSNS currently,
eventually becoming VFR at KSNS this afternoon with the potential
for KMRY to remain MVFR throughout the day. However, have KMRY
scattering out by 20Z in the current TAF. Have LIFR/IFR conditions
returning this evening and potentially lowering into the night,
however confidence is not great enough to include in the TAF at
this time.
&&
.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 200 PM PDT Mon Aug 17 2026
The marine layer will gradually compress over the next 24 to 36
hours, as high pressure builds over the region. As a result, nocturnal
drying will be possible through at least mid-week for the higher
elevations, with 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 Tuesday to 3 AM PDT Wednesday for
Pt Arena to Pt Reyes 10-60 NM.
&&
$$
SHORT TERM...Palmer
LONG TERM....Palmer
AVIATION...RGass
MARINE...RGass
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Prepared by Boulder-Creek.com Weather at: Mon Aug 17 16:30:03 PDT 2026
From the National Weather Service
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