807
FXUS66 KSEW 101008 CCA
AFDSEW

Area Forecast Discussion
National Weather Service Seattle WA
303 AM PDT Mon Aug 10 2026

.SYNOPSIS...
Zonal flow aloft and onshore flow will lead to daytime high
temperatures near seasonal normals today and again Tuesday. An upper
trough passing across British Columbia will cool temperatures
slightly and bring to a threat of showers in the North Cascades
midweek. Warmer conditions return at the end of the week as upper
ridging rebuilds over the region.

&&

.SHORT TERM /TODAY THROUGH WEDNESDAY/...
Latest satellite imagery showing marine stratus more advanced than
it was 24 hours ago, with cloudy conditions expected by sunrise
stretching at least into the east Puget Sound lowlands...possibly
even into some Cascade valleys. Current temps also reflecting this
more successful marine push, running on average 2 to 4 degrees
cooler than this time yesterday morning.

The forecast for today and Tuesday will remain consistent with the
general pattern that has been in place for the past few days.
Stratus likely to be burned off by late morning and enough daytime
heating to get daytime highs akin to what they were yesterday, if
maybe a degree or two shy. Latest models currently show that marine
stratus push tonight might not be as successful as the current one.
That will lead to clouds burning off quicker Tuesday and thusly a
degree or two of warming.

Consensus remains intact so far with regard to an upper level trough
passing just to the north of the Canadian border Wednesday. Any
potential rainfall from that system still looks to be confined to
the northern Cascades. Sufficient instability over that area will
also allow for the prospect of isolated thunderstorms in the
afternoon and evening. The more widespread impact from this passing
system will be a dip in daytime highs with mainly mid to upper 70s
in the interior lowlands and mid 60s along the coast.

18

&&

.LONG TERM /WEDNESDAY NIGHT THROUGH SUNDAY/...
Models put some splotches of potential precip over some locations in
W WA for Thursday...possibly due to a following shortwave...but it
is a feature you would have to squint to find. As such, confidence
remains low in this prospect, even though the NBM seems to have
latched on to it in the extended. Instead, more likely is the start
of a warming trend Thursday returning widespread lower 80s to the
interior lowlands, with the coast warming up to the upper 60s to
lower 70s. The heat remains on for Friday as highs for the interior
top out in the mid to upper 80s. This would result in
Moderate/Orange HeatRisk for the entire I-5 corridor stretching from
Olympia to Bellingham...with perhaps a small gap around Mt. Vernon.
For the weekend, nothing seems terribly impressive as models bring
through a pretty low amplitude ridge followed quickly by an inverted
counterpart of equally less impressive depth. These features are
generally dry and should only result in a gradual cooling trend for
the weekend. Even then, daytime highs for the interior are not
expected to escape from the 80s.

18

&&

.AVIATION...
Westerly flow aloft will persist through the TAF period, along with
onshore flow in the low levels. Marine stratus is currently making
its way inland into the interior this morning, and will continue to
filter in over the next few hours. This will bring a couple hours of
IFR to localized LIFR conditions to the area terminals before
stratus retreats back to the coast around mid to late morning.
Mostly clear skies will prevail thereafter for the inland terminals,
with some high cloud cover passing overhead.
Winds are mostly light, persisting at 5kt or less, across the area
this morning, except at KCLM where winds persist out of the west and
are breezy at times with a westerly push down the Strait of Juan de
Fuca. Winds will become more northerly across the interior and
increase to 5-10 kt during the afternoon hours. VFR conditions will
then prevail for most sites, except for KHQM on the coast, through
the remainder of the day. Another round of stratus looks to push
inland on Tuesday morning.

KSEA...VFR conditions with light winds at the terminal, primarily
around 5 kt or less. Latest guidance indicates a 30 to 35 percent
chance of stratus bringing a few hours of MVFR to IFR conditions to
the terminal between 13-17Z this morning. Expect conditions to
improve back to VFR by mid to late morning.
Winds will shift back to the north this afternoon and will persist
between 4-8 kt. Another round of stratus may push into the terminal
on Tuesday morning, with guidance highlighting similar probabilities
of 30-35 percent chance of MVFR conditions developing by early
Tuesday.

&&

.MARINE...
Broad surface high pressure will remain centered over the offshore
waters with lower pressure east of the Cascades through much of the
week ahead. This will maintain onshore flow over the next several
days and bring diurnally driven small craft advisory strength
westerlies to the central and east Strait of Juan de Fuca daily. A
series of weak systems passing to the north of the area throughout
the week may help strengthen onshore flow at times for additional
risks of gales along the central and eastern Strait.

Seas across the coastal waters will primarily persist at 4-6 feet
today, before subsiding towards 3-4 feet by Tuesday. Seas then look
to increase to 5-7 feet again near midweek and will persist within
the 3-6 foot range through the second half of the week.

&&

.FIRE WEATHER...
A dry, onshore flow pattern with seasonable temperatures and
persistent good to excellent overnight RH recoveries through
Tuesday. Ensembles continue to very confidently show an upper
level shortwave clipping the area Wednesday, with some
variability in the strength of the shortwave. This continues to
reinforce the scenario of thunderstorm potential Wednesday
afternoon and evening for the far northern Cascades. The NBM has
a 20-30% probability over the Whatcom, Skagit and Snohomish
Cascades through late Wednesday evening. Warmer and continued
dry conditions remain on track through the second half of the
week, likely resulting in a return of elevated fire weather
concerns for some areas.

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...None.
PZ...Small Craft Advisory until 5 AM PDT early this morning for
     Central U.S. Waters Strait Of Juan De Fuca-East Entrance
     U.S. Waters Strait Of Juan De Fuca.

     Small Craft Advisory from 3 PM this afternoon to 5 AM PDT
     Tuesday for Central U.S. Waters Strait Of Juan De Fuca-
     East Entrance U.S. Waters Strait Of Juan De Fuca.


&&

$$