411
FXUS66 KSEW 190311
AFDSEW

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

.UPDATE...Radar pretty quiet this evening across Western
Washington, with the front stalled offshore. Latest shower
activity currently to the north in Vancouver Island. May see some
light showers tonight across the northern coast. No significant
changes to the forecast this evening. Refer to an updated aviation
and marine section below.

&&

.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...An upper trough will remain offshore into Tuesday
which will result in continued southwest flow aloft. Generally light
flow in the lower levels. VFR conditions this evening with
widespread mid and high clouds. VFR conditions are expected to
continue into Tuesday morning for the interior. MVFR/IFR cigs to
develop along the coast early Tuesday morning. There is a slight
chance (around 15%) IFR cigs reach KPWT Tuesday morning. Otherwise,
VFR conditions Tuesday afternoon for most areas with mid and high
clouds. Light S/SW surface winds will increase Tuesday afternoon.

KSEA...VFR cigs through Tuesday with mid and high clouds. Light S/SW
winds tonight will increase again Tuesday afternoon. Winds may
transition more N/NW Tuesday evening (generally after 03z). JD

&&

.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. JD/Felton

&&

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

$$