468
FXUS66 KSEW 240243
AFDSEW

Area Forecast Discussion
National Weather Service Seattle WA
742 PM PDT Sun Aug 23 2026

.SYNOPSIS...
An upper level trough will exit Western Washington tonight. Drier
and warmer weather Monday and Tuesday as an upper level ridge builds
over the Pacific Northwest. An upper level low will approach the
area around midweek, bringing increasing onshore flow and cooler
temperatures to Western Washington for the second half of the week.

&&

.SHORT TERM /TONIGHT THROUGH TUESDAY NIGHT/...
The upper level trough continues its way out of the area this
evening with partly cloudy skies still present east of the Sound
while generally mostly cloudy conditions exist over much of the
Olympic Peninsula. While locations along the I-5 corridor are still
in the upper 60s to low 70s, the remainder of the area has already
cooled into the lower 60s to upper 50s. Quiet conditions overall
with inherited forecast on track. No evening updates anticipated.
For additional forecast details, please refer to the Previous
Discussion section below.

18

From Previous Discussion...An upper level trough continues to push
across Washington this afternoon. Partly cloudy skies this afternoon
with high temperatures in the low to mid 70s across the interior and
mid 60s along the coast. An upper level ridge will build over the
Pacific Northwest on Monday, with the ridge axis east of the
Cascades on Tuesday. This will bring warmer and drier conditions.
The warmest day will be Tuesday. High temperatures are expected to
peak in the mid 60s/low 70s along the coast. Across the interior,
temperatures will climb into the 80s and low 90s in the Cascade
valleys. This will reintroduce widespread areas of Moderate HeatRisk
for the Everret-Seattle-Tacoma Metro and Cascade valleys.

Additionally, surface flow will transition more northerly to
easterly Monday and Tuesday, resulting in wildfire smoke being
transported from nearby fires in British Columbia and Eastern
Washington into Western Washington. 29

&&

.LONG TERM /WEDNESDAY THROUGH SUNDAY/...
There is good agreement between ensemble guidance that an upper
level low will approach the Pacific Northwest on Wednesday and an
upper level trough will settle over the region through late in the
week. This pattern will reinstate onshore flow across Western
Washington and bring cooler temperatures. Latest guidance has high
temperatures trending slightly below normal in the the low to mid 60
along the coast and low to mid 70s across the interior. Low
temperatures by the end of the week will trend towards the low
to mid 50s. Chances for precipitation look to return on
Wednesday and continue into the weekend. However, the latest
QPF amounts indicate precipitation will be light. While
thunderstorm chances remain at 10% or less, they could be a
possibility on Wednesday and Thursday as the upper level low
swings north into British Columbia and brings southwesterly
flow aloft over Western Washington. 29

&&

.AVIATION...
An upper ridge begins to build into the area tonight through Monday,
which will result in westerly flow aloft becoming southwest on
Monday. VFR cigs this evening as cloud coverage dissipates in the
interior. LIFR stratus will develop along the coast tonight. LIFR
cigs are also expected across the Strait of Juan de Fuca by early
Monday. There remains uncertainty exists as to the extent of stratus
around central Puget Sound Monday AM. but KPAE has the highest
likelihood of seeing lower ceilings/visibilities in the morning.
Can`t also rule out patchy fog in low valleys with the clear
skies/weak north gradients. Otherwise, mainly VFR elsewhere with a
few high clouds on Monday with haze increasing aloft late Monday
with more of an E flow in the mid levels. Winds at the surface will
transition more north this evening, increasing from the north Monday
afternoon.

KSEA...VFR cigs this evening with clearing skies. LIFR stratus will
push inland along the Strait of Juan de Fuca into early Monday, but
the likelihood of it reaching KSEA remains at 10% between 13-17z, as
model solutions have it getting stopped at KPAE. Winds remain N to
NE tonight at 5 to 9 kts, and into Monday. JD/HPR

&&

.MARINE...
High pressure continues to build over the Coastal Waters today
and will remain in place through Tuesday. North winds will
increase on Monday, particularly for the Coastal Waters and
Puget Sound. Will need to monitor for SCA wind gusts late Monday
afternoon through Monday evening for the Coastal Waters, with
current probabilities of SCA gusts around 40 to 70 percent
during this period. Onshore flow then increase Tuesday night
through Wednesday as a weak frontal system moves across the
waters midweek. This may result in SCA west winds through the
Strait of Juan de Fuca beginning Tuesday night. Onshore flow
then continues late in the week.

Seas around 3 to 5 feet may briefly peak towards 7 feet for the
southern Coastal Waters late Monday with increasing north winds.
This may lead to brief choppy waters with a period around 6 seconds.
Otherwise, 4 to 5 foot seas are expected Tuesday through much of the
week. JD

&&

.FIRE WEATHER...
Guidance is in lock-step regarding a ridge building into the region
on Monday into Tuesday. A thermal trough will also snake along the
coast during this time, leading to a warm-up and drier conditions as
light offshore flow develops. Isolated areas of min RHs reaching
near critical thresholds are possible during this time in the
Cascades. Onshore flow then returns Tuesday night into Wednesday as
another upper-trough enters the region. Showers as well as the
chances for more thunderstorms are possible around the midweek
timeframe.

Less certainty in how the pattern will evolve towards the second
half of the week. Solutions are hinting at an upper-trough swinging a
pair of upper-lows into the region but there is disagreement in
exact timing and track. Nonetheless, below normal temperatures,
onshore flow and the potential for precipitation appears to be in
the offing towards the weekend.

41

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...None.
PZ...None.

&&

$$