FXUS66 KMTR 180649
AFDMTR
Area Forecast Discussion
National Weather Service San Francisco CA
1149 PM PDT Mon Aug 17 2026
...New SHORT TERM, LONG TERM...
.KEY MESSAGES...
Updated at 428 PM PDT Mon Aug 17 2026
- Slight warming trend continues through Wednesday
- Marine layer remains compressed through mid week
- Light winds continue to be mitigating factor for
Timber Fire
&&
.SHORT TERM...
Issued at 1145 PM PDT Mon Aug 17 2026
(Today and tonight)
Mid/upper level clouds continue to stream from southwest to
northeast across our area with mild temperatures expected once again
overnight into early Tuesday morning. The mild start to the day will
help bump temperatures at least a few degrees (away from the marine
layer) higher from Mondays values as the influence from upper level
ridging over the Four Corners nudges west. H85 temperatures will be
around 23-24C by peak heating which is in the 90th percentile for
this time of year. With that, the warmest temperatures will be at
higher elevations, especially the East Bay Hills and Santa Lucias,
including higher portions of the Timber Fire. Fortunately, light
winds continue to be a mitigating factor to more rapid spreading of
the fire.
&&
.LONG TERM...
Issued at 1145 PM PDT Mon Aug 17 2026
(Wednesday through Monday)
Warmer temperatures persist Wednesday under the influence of the
aforementioned ridging aloft, however the troughing over the EPAC
pushes back east and slightly north by Thursday with a sharpening
trough axis well offshore. The cool down for Thursday through the
remainder of the extended forecast will be subtle and gradual.
There are at least two tropical waves that will pass well to our
south, the first on Thursday followed by a more organized wave
with tropical development possible by the end of the weekend into
the beginning of next week. We'll be keeping an eye on any
midlevel moisture advection north from either of the two waves.
&&
.AVIATION...
(06Z TAFS)
Issued at 959 PM PDT Mon Aug 17 2026
IFR-LIFR stratus is expanding inland with high clouds making it
difficult to gauge the extent of the stratus deck in several areas
across the North Bay and SF Bay regions, while a moderate northwest
breeze persists for a couple more hours. Stratus will generally
impact most of the terminals through the overnight period with low
confidence of impacts at LVK. May need to monitor observations to
see if the high clouds result in impaired stratus development at
STS. Stratus will mix out back to the coastal regions on Tuesday
morning, with gentle to moderate onshore breezes developing in the
afternoon and evening. Tuesday night, expect lower ceilings and less
inland stratus development near and beyond the end of the TAF period
as the marine layer continues to compress.
Vicinity of SFO... IFR stratus continues through the night with
lingering moderate winds diminishing in the next couple of hours.
The stratus deck will mix out on Tuesday morning with breezy
northwest winds resuming in the afternoon. Tuesday night, the
terminal area sits at the edge of where high resolution model output
paints the stratus deck, making the forecast for stratus impacts and
development time low to moderate confidence.
SFO Bridge Approach... Lower confidence for stratus impacts on
Tuesday night compared to the terminal area. Otherwise similar to
SFO.
Monterey Bay Terminals... IFR stratus has developed across the
region with a decrease to LIFR ceilings expected through the night.
The stratus will mix out through Tuesday morning, with some
uncertainty on clearing times. Moderate confidence that MRY will
scatter out sometime Tuesday afternoon. Light winds will persist
through Tuesday morning before gentle to moderate northwest winds
resume in the afternoon and evening. Opted for a persistence
forecast for IFR-LIFR stratus returning to the terminals early
Tuesday evening.
&&
.MARINE...
(Tonight through next Sunday)
Issued at 914 PM PDT Mon Aug 17 2026
A fresh to strong northwest breeze will develop tonight and
persist 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 subsiding later in the 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...JM
LONG TERM....JM
AVIATION...DialH
MARINE...DialH
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Prepared by Boulder-Creek.com Weather at: Tue Aug 18 02:30:02 PDT 2026
From the National Weather Service
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