491
FXUS66 KSEW 101521
AFDSEW

Area Forecast Discussion
National Weather Service Seattle WA
821 AM PDT Sun Aug 10 2025

.SYNOPSIS...High pressure will continue to build into the
region through early next week, bringing a warming and drying
trend. Widespread Moderate (Orange) HeatRisk will continue
across the lowlands through Tuesday, and a Heat Advisory remains
in effect across the lowlands. An upper trough will move into
the area towards the second half of next week, bringing in
cooler and cloudier conditions with increasing chances for rain.

&&

.UPDATE...Clear skies are in place across western WA this
morning with the exception of some localized smoke from the Bear
Gulch fire in Mason County and fog in the lower Chehalis River
Valley and Grays Harbor (which will burn off this morning). The
current forecast is on track an no updates are planned this
morning.
-Wolcott-

&&

.SHORT TERM /TODAY THROUGH TUESDAY/...A ridge of high pressure
centered over the Pacific will continue to amplify through the
short-term, resulting in warm and dry conditions across western
Washington. Fog and low stratus has set up along the Pacific
Coast and through the Strait of Juan de Fuca early this morning,
but will burn off by the afternoon with clear skies and warming
resuming across the region. Temperatures today will reach the
mid to upper 80s across much of the lowlands, with pockets of 90
degrees across the Chehalis River Basin southwest of Olympia.
This will result in widespread Moderate (Orange) HeatRisk across
the lowlands, and elevated overnight low temperatures in the
upper 50s to low 60s will provide little relief to the daytime
heat. A Heat Advisory remains in effect across most lowland
areas for Sunday afternoon, and the Advisory continues through
Tuesday evening as temperatures will remain elevated.

Warming will continue on Monday as high pressure continues to
build into western Washington. As a thermal trough forms along
the coast, Monday will be the warmest day for coastal areas.
Temperatures will increase into the upper 80s and low 90s across
the region, with the warmest temperatures southwest of the Puget
Sound and southward along the I-5 corridor. Clear skies and light
winds will prevail once again, with even warmer overnight lows in
the mid 60s for much of the lowlands.

The thermal trough will shift inland on Tuesday, resulting in
even warmer temperatures across the interior lowlands and subtle
cooling along the coast. While some uncertainty remains over
temperatures on Tuesday, ensembles maintain high chances of 90
degrees or higher across the metro areas east and south of the
Puget Sound. Ensembles show a moderate (60% to 70%) chance of
reaching 90 degrees on Tuesday in Seattle, and a higher (70% to
80%) chance of 90 degrees or higher in Olympia. The warmest
temperatures are on track to occur south of the Puget Sound and
along the Cascade Foothills, with continued widespread Moderate
HeatRisk across the lowlands.

.LONG TERM /WEDNESDAY THROUGH SATURDAY/...While forecast models
continue to struggle to predict the breakdown of the upper ridge,
most ensemble members show a pattern change by Wednesday with a
trough moving over the Pacific Northwest. This will bring
temperatures back to near-normal, peaking in the upper 70s across
the lowlands and in the mid to upper 60s along the coast.
Increased onshore flow will promote continued cooler temperatures
and periods of cloudy skies through the remainder of the week as a
series of troughs is set to pass over the region. Chances for
rainfall increase Thursday through Saturday, primarily over higher
terrain, but the exact placement and intensity remains uncertain
at this time.

15

&&

.AVIATION...Upper level ridge with northwesterly flow aloft into
Monday. Northwesterly surface gradients today going light tonight
into Monday as thermally induced surface trough moves up the
coastline then inland Monday.

The fog has began to scatter out of KHQM this morning and conditions
have improved. IFR/LIFR stratus returning to the coast after 02z-03z
tonight. Otherwise, VFR will prevail for the rest of the terminals
today.

KSEA...Mostly clear skies today, with VFR prevailing. Northeast wind
6 to 10 knots this morning becoming north northwest 10 to 12 knots
around 18z-19z. Winds easing to northeast 4 to 8 knots after 04z
tonight.

Felton/29

&&

.MARINE...High pressure will remain over the coastal waters through
Wednesday. A thermally induced surface trough will move up the
coastline tonight then shift inland Monday and Tuesday. High
pressure will weaken Wednesday with a weak trough moving into the
coastal waters Thursday.

Small Craft Advisory for the outer coastal waters today for choppy
seas at 7 or 8 feet with 8 to 9 second period, with winds increasing
to 15 to 25 knots and seas building to 10 feet tonight. On Monday,
seas will continue building to 10 to 13 feet. Strong possibility
that small craft advisory conditions will continue over the outer
coastal waters until at least Tuesday night.

Small craft advisory westerlies possible for the Central and Eastern
Strait of Juan de Fuca Tuesday.

Felton

&&

.FIRE WEATHER...A warming and drying trend will continue today
through Tuesday as an upper level ridge builds over the area and
a weak resultant thermal trough develops along the coast. This
will allow for minimum RH values today through Tuesday to dip as
low as 25-35%, with the lowest RH values from the south Puget
Sound, the southwest interior, and the southern Washington
Cascades. A shortwave trough looks to move through late Sunday
into Monday, and along with the thermal trough, will result in
poorer RH recoveries and may slightly increased atmospheric
instability, potentially resulting in more activity on our
ongoing fires. More persistent troughing is expected to develop
into Wednesday, allowing for cooler and more moist air to return
to the region with a slight chance for light showers for
portions of the North Cascades and the Pacific coast beginning
Thursday.

62

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...Heat Advisory from 2 PM this afternoon to 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 PM PDT Monday 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.

&&

$$