731
FXUS66 KSEW 120343
AFDSEW
Area Forecast Discussion
National Weather Service Seattle WA
843 PM PDT Mon Aug 11 2025
.SYNOPSIS...Hot and dry conditions will continue Tuesday with
widespread Moderate HeatRisk values. 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 needed widespread rain moving into
the region Friday into Saturday.
&&
.SHORT TERM /TONIGHT THROUGH WEDNESDAY NIGHT/...The upper level
ridge over 140 W will continue to drive very warm and dry
conditions over the Pacific Northwest through Tuesday.The heat
advisory remains in effect across the western Washington
lowlands through Tuesday evening. Temperatures this afternoon
reaching into the upper 80s and low 90s as of midafternoon
especially along the north coast and interior from Tacoma
southward. Overnight low temperatures will remain in the 60s for
many areas tonight, providing little relief from the daytime
heat - especially through the metro area. The thermal trough
building along the Pacific Coast will shift inland Tuesday,
allowing temperatures to cool slightly along the coast - but
remain warm further inland, peaking in the low to mid 90s south
and east of the Puget Sound. This will result in widespread
Moderate (Orange) HeatRisk across the region, and pockets of
Major (Red) HeatRisk between Seattle and Tacoma. As the upper
level ridge starts to break down Tuesday evening and the surface
trough shifts inland, westerly winds will increase and cooler
higher humidity air will slowly filter inland.
The upper level ridge will weaken Wednesday as an upper level
trough passes to the north over British Columbia. Strengthening
onshore flow will bring a more robust marine layer and much
needed relief from the heat. Temperatures will cool considerably,
peaking in the 60s and 70s on Wednesday.
&&
.LONG TERM /THURSDAY THROUGH MONDAY/...Cooler and cloudy
conditions will continue through the period as a series of
systems pass through the region, with increasing chances for
rain heading into the weekend. Most notably will be a system
moving onshore late Thursday/Friday into Saturday that ensembles
are indicating will result in a 70-90% chance of widespread
wetting rain (amounts 0.25 in or more) over a 24 to 36 hour
period. In addition, temperatures will remain on the cool side
for mid August through the weekend. The unusually cool air mass
may even allow snow levels to drop as low as 8500 feet resulting
in light snow over the peaks of Rainier and Baker Saturday.
Unsettled weather will linger into Sunday, and some chance of a
drier trend Monday.
&&
.AVIATION...An upper level ridge will remain centered offshore
into Tuesday with northwest flow aloft over Western Washington.
Thermally induced low pressure near the coast will shift into
the interior overnight with low level offshore flow transitioning
to light onshore. LIFR coastal stratus will gradually shift
northward from the Oregon coast overnight and is expected to
reach the central Washington coast by early Tuesday A.M. before
scattering out late morning. VFR continues elsewhere.
KSEA...VFR. Surface winds northerly 10 to 15 knots this afternoon
will ease to light northeasterly overnight. Winds will shift to W/NW
7 knots or less Tuesday morning. 27
&&
.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 tonight and
remain through Tuesday. The trough will shift east of the Cascades
Tuesday night. A front will reach the coastal waters Friday.
Increasing onshore flow will lead to small craft advisory winds/seas
over the outer coastal waters today through late Tuesday as well as
likely small craft advisory strength westerlies in the central and
east strait Tuesday evening into late Tuesday night. 27
&&
.FIRE WEATHER...Very warm and dry conditions will continue
across western Washington into Tuesday, with high pressure aloft
and the thermally induced surface trough slowly shifts inland.
With temperatures in 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
today will linger into Tuesday over the Olympics and Cascades,
which may result in increased activity on ongoing fires in the
area. This will maintain 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 elevated
probabilities of wetting rains 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.
&&
$$