355
FXUS66 KSEW 220346
AFDSEW

Area Forecast Discussion
National Weather Service Seattle WA
846 PM PDT Thu Aug 21 2025

.SYNOPSIS...Unusually hot and continued dry conditions will
linger well into next week. Major HeatRisk levels can be
expected through the Cascade foothills/valleys and widespread
Moderate HeatRisk levels over much of the remaining lowland
areas. In addition, elevated fire weather countdowns are
expected, with pockets of extreme conditions especially in the
Cascades and eastern Olympic Mountains.

&&

.SHORT TERM /TONIGHT THROUGH SATURDAY NIGHT/...Solid upper
level ridging over the region is setting the stage for unusually
hot and dry conditions across western WA. This will get a boost
from offshore/easterly winds Friday into Saturday as a
thermally induced surface trough builds northward into
southwestern Washington. Temperatures will peak over the weekend
with most lowland areas seeing highs in the mid 80s to 90s,
with triple digits possible in the Cascade valleys. Overnight
lows will be mainly in the 60s, with many area in the
metro/urban areas and foothills only cooling into the mid 60s
overnight Saturday into Sunday morning and again Sunday night
into Monday morning. Major HeatRisk values are expected through
the foothills and valleys of the Cascades, as well as for
portions of the metro area - especially along the I-5 corridor
eastward. Elsewhere, Heat Risk remain mostly Moderate for the
region. An Extreme Heat Warning is in effect for the
foothills/valleys of the Cascades and a Heat Advisory is in
effect for most of the remaining lowlands of western WA. In
addition, fire danger remains elevated due to the warm and dry
conditions, with some chance of pockets of extreme conditions in
the Cascades and eastern Olympic Mountains.. Min RHs will be in
the 20s and teens, especially around the south sound and in the
mountains.

&&

.LONG TERM /SUNDAY THROUGH THURSDAY/...Ensembles continue to
highlight persistent upper level ridging well into next week -
resulting in higher confidence for continued warm and dry
conditions. Above normal temperatures in the mid 80s and 90s and
continued dry. Weak onshore pushes may bring some periods of
relief to the coast but interior temps will remain warm. The
range of possibilities particularly with respect to high
temperatures remains more broad into mid week, but there remains
a good chance of Moderate Heat Risk coverage lingering into
Tuesday, and solid chances of at least warmer than normal
temperatures through much of next week. It is of note that there
are some hints in the models of mid level moisture pushing
northward (high- based showers) mid week - which could result in
some potential for convection mainly along the Cascades Tuesday
into Wednesday.

&&

.AVIATION...Westerly flow aloft as an upper level ridge continues to
build over western Washington. Widespread VFR conditions in place
and expected to remain throughout the TAF period. HQM may see some
vis restrictions very early Friday morning due to marine influence,
but confidence is shaky given that there were no stratus this AM and
onshore push is even weaker overnight tonight. Surface winds remain
mostly northerly, with some variation to the NW or NE due to
terrain, with speeds ranging 5-10 kts this evening, easing to 3-7
kts overnight. Speeds expected to return to 5-10 kts or so late
Friday morning through Friday evening.

KSEA...VFR conditions for the duration of the TAF period with
northerly winds 6 to 12 knots decreasing overnight into Friday
morning. Speeds expected to be akin to what is described above.

Mazurkiewicz/18

&&

.MARINE...Surface ridging will continue over the coastal waters
as a thermally induced low pressure expands northward over the
coast. Breezy northerly to northwesterly winds can be expected
at times over the coastal waters but will stay under small craft
advisory criteria. Thermal troughing will shift more inland
early next week which will bring light onshore flow throughout
the waters.

Combined seas 3 to 5 feet will continue throughout the weekend and
into the early half of next week.

Mazurkiewicz

&&

.FIRE WEATHER...An upper level ridge building over the area
into this weekend will bring a warming and drying trend to
western Washington resulting in elevated to critical fire
weather conditions. Periods of offshore flow will be possible
throughout Friday and Saturday, which will help quickly dry out
fuels from recent rains. Hot, dry, and unstable conditions will
exceed extreme fire weather criteria for the Cascades and east
Olympic mountains.

The elevated fire weather conditions are expected to be
widespread across the rest of the Cascades and areas south of
the Sound into the the weekend. High temperatures will be in the
upper 80s to upper 90s with minimum RHs dipping into the 15-30
percent range. Overnight RH recoveries will be relatively poor
to moderate over the weekend due to the aforementioned periods
of offshore flow. Warm and dry conditions look to linger into
the early half of next week.

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...Fire Weather Watch from Saturday morning through Sunday
     evening for West Slopes of the Central Cascades Generally
     above 1500 Feet-West Slopes of the North Cascades
     Generally above 1500 Feet.

     Extreme Heat Warning from 11 AM Friday to 5 AM PDT Tuesday for
     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.
     Heat Advisory from 11 AM Friday to 5 AM PDT Tuesday for City
     of Seattle-Downtown Everett / Marysville Area-Eastern
     Kitsap County-Eastside-Foothills of the Western and
     Southern Olympic Peninsula-Lake Crescent Area Including
     US 101-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.

     Fire Weather Watch from Saturday morning through Saturday
     evening for East Portion of the Olympic Mountains.

PZ...None.

&&

$$