731
FXUS66 KSEW 241532
AFDSEW

Area Forecast Discussion
National Weather Service Seattle WA
832 AM PDT Sun Aug 24 2025

.SYNOPSIS...Longer duration heat and dry conditions are going to
continue into next week as high pressure remains in the region.
Widespread Moderate (orange) to Major (red) HeatRisk is forecast
through Monday and possibly into Tuesday for western Washington.
Critical fire weather is ongoing through today and into Monday
for the Cascades and eastern slopes of the Olympics.

&&

.SHORT TERM /TODAY THROUGH TUESDAY/...The latest forecast remains
on track with no updates this morning. High pressure amplifying
into the region will keep the hot temperatures in the forecast
today and into early next week. Though relative and gradual
cooling is expected to take place after today, temperatures are
still going to be much above average into the middle of next week,
with warm overnight lows. The warmer overnight temperatures
(generally 60 to 65 degrees) will keep moderate to major HeatRisk
in play into late Tuesday. These temperatures don`t offer relief
from the heat of the day and can act to amplify heat stresses and
illnesses. Cascade foothill valley locations could see a repeat of
triple digit temperatures today with widespread 90 degree
temperatures throughout the rest of Puget Sound and Chehalis
Valley. An Extreme Heat Warning remains posted for the major metro
areas and Cascade foothills and valleys with heat advisories
elsewhere away from the coast.

The high pressure system keeping the temperatures high will begin
to falter a bit come Monday, with light onshore flow developing as
an offshore trough begins to take shape. Highs on Monday dip one
to two degrees for upper 80s and low 90s, then on Tuesday-slightly
more cooling down into the upper 80s for western Washington. Some
of the models are suggestive of some moisture from the monsoon in
the Desert Southwest being drawn up into the northwest by this
area of low pressure and bringing a slight chance for
thunderstorms on Monday, potentially into Tuesday. This solution
is low confidence, but the latest convective outlook from the
Storm Prediction Center does show the area highlighted in the
general thunder category for Monday into Tuesday. Surface CAPE
values over the Cascades are high, generally still indicating 1000
to 2000 J/kg which is more than enough instability for
thunderstorms should the rest of the pattern be supportive of it.
Precipitable water values for Monday into Tuesday show a climb of
1 to 1.5 inches, also suggesting that storms could be wet. If
anything develops, the favored area would be along the crest of
the Cascades, beginning in southern Washington and moving north.


.LONG TERM /WEDNESDAY THROUGH SATURDAY/...As the trough lingers
offshore, more southerly flow aloft and lingering moisture could
make for another thunderstorm threat on Wednesday. That low could
send shortwaves off the core, promoting instability and
thunderstorm potential-primarily in the Cascades. Temperatures on
Wednesday are likely to be back closer to what is normal, in the
upper 70s to low 80s.

The model cluster analysis has been generally consistent with
showing the trough still offshore through mid to late week. There
are still considerable inconsistencies on the trough positioning
and timing which has impacts on the sensible weather. Confidence
in temperatures returning back to the mid 70s by next weekend is
reasonable.

Kristell

&&

.AVIATION...South to southwesterly flow aloft continues through
Sunday with an upper ridge situated over the Pacific Northwest. VFR
conditions with a few high clouds around this morning. VFR
conditions are expected to continue through Sunday for the majority
of terminals with high clouds at times. Stratus may move into KHQM
this morning, mainly between 12 to 18z, resulting in brief LIFR/IFR
cigs. Confidence remains higher in stratus moving into KHQM Sunday
night into Monday morning. Light winds this morning will increase
from the N/NW this afternoon.

KSEA...VFR conditions through the TAF period with a few passing high
clouds at times. N/NE surface winds this morning of 4 to 7 kts will
increase from the NW to 7 to 12 kts this afternoon.

JD

&&

.MARINE...Surface high pressure will continue over Western
Washington today with continued northerly flow. Elevated north to
northwesterly winds are expected at times for the outer portions of
the Coastal Waters through late Monday. Occasional wind gusts of 20
to 25 kts will be possible in these areas, but sustained winds are
expected to be primarily below SCA threshold. Northerly winds will
continue for the interior waters through Tuesday. Onshore flow is
then expected to increase by midweek.

Seas will be 4 to 6 feet through today, building to 7 feet for the
far Outer Coastal Waters tonight through Monday. This may result in
steep seas at times for the far Outer Coastal Waters with a dominant
period of 7 to 8 seconds. Seas will then subside to 3 to 5 feet by
midweek.

JD

&&

.FIRE WEATHER...Red Flag Warnings for the west slopes of the
Cascades and east slopes of the Olympics remains in effect through
9PM today for hot, dry and unstable conditions. There is the
possibility that the fire weather watch on Tuesday could be
upgraded to a red flag warnings given the thunderstorm threat on
Monday into Tuesday, particularly for the Cascades. Unstable
conditions are forecast for early next week as troughing rebuilds
offshore and sends shortwaves into western Washington while also
tapping into moisture aloft from monsoonal activity in the
Southwest. There is a threat for thunderstorms Monday through
Wednesday (with Tuesday and Wednesday looking like the better
chance days at 15-20%) and will likely be focused along the
Cascades. Precipitable water values climb over an inch, suggesting
that any thunderstorms that develop may have a better chance of
bringing about a wetting rain (0.25 inches), but will still be
capable of dangerous lightning and erratic winds.

Minimum RH this afternoon will be low again as temperatures are
hot. Upper teens to low 20 percents are expected in the Cascades,
with 20 to 30 percent along the eastern Olympics. A look at RH
recoveries early this morning are not promising at 25-35 percent,
locally lower in the north Cascades as northeast winds have
persisted overnight.

Bear Gulch Fire:
Something to watch in the short term will be the thermal trough
advancing inland from the coast as the ridge begins to break down
on Monday. Looking at the MSLP forecast into Monday generally
shows the thermal trough moving over the fire somewhere early to
mid afternoon on Monday. The instability this provides is enough
to facilitate pyrocumulus development and breezier winds flowing
toward the fire and oxygenating its consumption.

Later in the week, the situation is more unclear, but gradual
onshore flow returning as the trough remains offshore should
improve the relative humidity recoveries and dampen the
conditions.

Kristell

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...Red Flag Warning until 9 PM PDT this evening for East Portion of
     the Olympic Mountains-West Slopes of the Central Cascades
     Generally above 1500 Feet-West Slopes of the North Cascades
     Generally above 1500 Feet.

     Fire Weather Watch from Monday afternoon through Tuesday 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 until 5 AM PDT Tuesday for City of Seattle-
     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-
     Lowlands of Pierce and Southern King Counties.

     Heat Advisory until 5 AM PDT Tuesday for Downtown Everett /
     Marysville Area-Eastern Kitsap County-Foothills of the
     Western and Southern Olympic Peninsula-Lake Crescent Area
     Including US 101-Lowlands of Lewis and Southern Thurston
     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...None.
&&

$$