165
FXUS66 KSEW 182118
AFDSEW

Area Forecast Discussion
National Weather Service Seattle WA
218 PM PDT Mon Aug 18 2025

.SYNOPSIS...Cooler conditions with cloudy skies and periods of
showers along the coast will continue through the middle of the
week as troughing continues offshore. A warmer and drier pattern
will develop into the weekend as high pressure builds over the
southwestern US.

&&

.SHORT TERM /TONIGHT THROUGH THURSDAY/...A decaying frontal system
will continue to bring in light shower activity across western
Washington this afternoon, with little to no rain accumulation.
The parent upper level trough will remain offshore today and
Tuesday, maintaining cooler conditions and cloudy skies. Highs
today and Tuesday will reach the mid to upper 70s across the
lowlands and the mid to upper 60s along the coast.

The upper trough will shift inland over British Columbia on
Wednesday, bringing brief zonal flow to the Pacific Northwest.
Onshore flow will promote another cloudy morning across the
region, breaking up by the afternoon to reveal sunny skies.
Temperatures will hold steady across the region, peaking once
again in the mid to upper 70s across the lowlands and mid to upper
60s along the coast.

By Thursday, an upper level ridge will begin to build over the
southwestern US and an upper level low will develop over the Gulf
of Alaska. Temperatures will increase a few degrees into Thursday
as high pressure builds northward into western Washington,
returning to near normal for the middle of August. Clouds are
favored to develop Thursday morning along the coast and through
the Strait of Juan de Fuca, giving way to sunny skies by the
afternoon.

.LONG TERM /FRIDAY THROUGH MONDAY/...Conditions will continue to
warm up and dry out into the weekend as high pressure continues to
build northward. Temperatures will reach the low to mid 80s across
the lowlands on Friday, which will be the warmest day of the
period. This will also result in areas of Moderate (Orange)
HeatRisk in metro areas east and south of the Puget Sound.
Temperatures will remain fairly steady into Saturday under the
influence of high pressure aloft. The ridge will break down
towards the end of the weekend, bringing temperatures back to
near-normal. Conditions will remain sunny and dry through the long
term.

15

&&

.AVIATION...Mostly VFR through the TAF period with passing mid and
high clouds in southwest flow aloft. Patchy IFR stratus is favored
to develop along the Pacific coast early Tuesday morning between
12z-18z. Surface winds will generally remain south to west 10 kt
or less through the period.

KSEA...VFR with a SCT-BKN cloud deck around 5000-6000 ft this
afternoon. Clouds will continue to scatter throughout the evening
and redevelop to low end VFR overnight. South to southwest surface
winds 7-10 kt will shift westerly this evening between 21z-05z
and shift back to southerly and ease overnight.

15

&&

.MARINE...Weak high pressure over the waters through Tuesday will
strengthen Tuesday night into Wednesday and remain over the waters
through Friday. A weakening system will try and move through the
high tonight dissipating over the coastal waters Tuesday.

No headlines the next few days. Diurnal westerly pushes through
the Strait of Juan de Fuca each evening Tuesday through Friday but
winds forecast to stay below 20 knots.

Felton

&&

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

$$