387
FXUS66 KSEW 110955
AFDSEW

Area Forecast Discussion
National Weather Service Seattle WA
255 AM PDT Mon Aug 11 2025

.SYNOPSIS...Hot and dry conditions will continue into Tuesday as
high pressure continues to build into western Washington.
Widespread Moderate (Orange) HeatRisk will continue through
Tuesday, and a Heat Advisory remains in effect across the lowlands.
Cooler and cloudy conditions will return Wednesday through the
remainder of the week as troughing moves over the region, with
widespread rain on tap over the weekend.

&&

.SHORT TERM /TODAY THROUGH WEDNESDAY/...A ridge of high pressure
centered over the Pacific will continue to amplify through
Tuesday, maintaining hot and dry conditions across western
Washington. A Heat Advisory remains in effect across the western
Washington lowlands through Tuesday evening. Temperatures today
will continue to rise under clear skies, reaching the upper 80s to
low 90s across the lowlands and in the upper 70s to 80s along the
Pacific Coast. This will result in widespread Moderate (Orange)
HeatRisk across the region, and an increase in forecast
temperatures has resulted in small pockets of Major (Red)
HeatRisk between Seattle and Tacoma, along with areas south of the
Puget Sound along the I-5 corridor and some of the Cascade
mountain valleys. Elevated overnight lows will once again provide
little relief from the daytime heat, staying in the mid 60s across
the interior lowlands.

A thermal trough building along the Pacific Coast will shift
inland on Tuesday as high pressure persists overhead. This will
allow temperatures to cool slightly along the coast, but
temperatures further inland will continue to increase and peak in
the low to mid 90s south and east of the Puget Sound. The warmest
temperatures are forecast southwest of the Puget Sound across the
Chehalis River Basin and southward through Centralia, and along
the Cascade Foothills and valleys, where temperatures could get
well into the 90s. As the upper level ridge starts to break down
Tuesday evening, westerly winds will increase and cooler, wetter
air will slowly filter inland.

Forecast models have come into better agreement over the upper
level ridge breaking down by Wednesday as a trough lowers over
western Canada. Onshore flow will increase, bringing in cloudy
skies and much needed relief from the heat. Temperatures will cool
considerably, peaking in the 60s and 70s on Wednesday.

.LONG TERM /THURSDAY THROUGH SUNDAY/...Cooler and cloudy
conditions will continue through the period as a series of troughs
move over the region, with increasing chances for rain heading
into the weekend. Temperatures through the long term will remain
on the cool side for mid August, with most areas struggling to
reach 70 degrees on Friday. A deep upper low is on track to spread
precipitation across western Washington on Friday and Saturday,
with preliminary rain totals of up to an inch over the lowlands
and 1 to 3 inches of rain over the mountains. The cooler air will
allow snow levels to drop as low as 8500 feet on Saturday,
resulting in light snow over the peaks of Rainier and Baker.
Ensembles maintain chances for showers to linger into Sunday,
continuing to bring some much needed moisture to the region.

15

&&

.AVIATION...Upper level ridge centered offshore with northwesterly
flow aloft through Tuesday. At the surface thermally induced
surface trough along the coast shifting into the interior today.
Low level offshore flow becoming light tonight into Tuesday.

Areas of LIFR fog along the coast and near the Strait of Juan de
Fuca will dissipate by 16z. Some high clouds for the remainder of
the area.

KSEA...VFR with high clouds at times. Northerly wind 3 to 6 knots
except 8 to 12 knots 20z-03z.

Felton

&&

.MARINE...High pressure will remain over the coastal waters through
Wednesday night then weaken Thursday. A thermally induced surface
trough along the coast will move over the inland waters today and
remain through Tuesday. The trough will shift east of the Cascades
Tuesday night. A front will reach the coastal waters Friday.

Small craft advisory outer coastal waters through at least Tuesday
night for seas 10 to 12 feet with a 10 second period and northerly
winds occasionally 20 to 25 knots. Winds and seas easing
Wednesday.

Small craft advisory westerlies expected in the Central and
Eastern Strait of Juan de Fuca Tuesday night.

Felton

&&

.FIRE WEATHER...A warming and drying trend will continue across
western Washington today and Tuesday as high pressure builds aloft
and a resultant thermal trough slowly shifts inland. As
temperatures increase into the upper 80s and lower 90s for most
areas, RH values will drop as low as 20% to 35% across much of the
region with poor overnight recoveries. Atmospheric instability
will also increase today and Tuesday over the Olympics and
Cascades, which may result in increased activity on ongoing fires
in the area. This will cause elevated fire weather concerns for
western Washington through Tuesday, and conditions will continue
to be closely monitored.

The upper ridge is forecast to break down on Wednesday as
more persistent troughing moves over the region, allowing for
cooler and more moist conditions to return. Chances for rainfall
increase towards the end of the week, with wetting rains possible
by Friday.

15

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...Heat Advisory until 10 PM PDT Tuesday for City of Seattle-
     Downtown Everett / Marysville Area-Eastern Kitsap County-
     Eastern Strait of Juan de Fuca-Eastside-Foothills and
     Valleys of Central King County-Foothills and Valleys of
     Pierce and Southern King Counties-Foothills and Valleys of
     Snohomish and Northern King Counties-Foothills and Valleys
     of Thurston and Lewis Counties-Foothills and Valleys of the
     North Cascades-Foothills of the Western and Southern
     Olympic Peninsula-Lake Crescent Area Including US 101-Lower
     Chehalis River Valley-Lowlands of Lewis and Southern
     Thurston Counties-Lowlands of Pierce and Southern King
     Counties-Lowlands of Western Skagit and Northwestern
     Snohomish Counties-Lowlands of Western Whatcom County-
     Middle Chehalis River Valley-Northern Hood Canal-Olympia
     and Southern Puget Sound-Shoreline / Lynnwood / South
     Everett Area-Southern Hood Canal-Willapa and Black Hills.

PZ...Small Craft Advisory until 6 AM PDT Wednesday for Coastal Waters
     From Cape Flattery To James Island 10 To 60 Nm-Coastal
     Waters From James Island To Point Grenville 10 To 60 Nm-
     Coastal Waters From Point Grenville To Cape Shoalwater 10
     To 60 Nm.

&&

$$