445
FXUS66 KSEW 222219
AFDSEW

Area Forecast Discussion
National Weather Service Seattle WA
319 PM PDT Fri Aug 22 2025

.SYNOPSIS...An extended period of unusually hot and dry conditions
will persist well into next week as high pressure builds into the
region. Widespread areas of Moderate (Orange) to Major (Red)
HeatRisk are expected through Monday across most of western
Washington. In addition, critical fire weather conditions are
expected in the Cascades and eastern Olympic Mountains over the
weekend.

&&

.SHORT TERM /TONIGHT THROUGH MONDAY/...High pressure will continue
to build over the region through the short term, resulting in
prolonged hot and dry conditions across western Washington.
Temperatures are well on the way today to reach the upper 80s to
low 90s across much of the lowlands away from the water, and
temperatures will continue to increase into Saturday and Sunday.
Saturday is on track to be the hottest day of the forecast period,
with some areas along the Cascade Foothills and through the
Cascade Valleys nearing 100 degrees. The rest of the lowlands away
from the water will see highs this weekend in the upper 80s to mid
90s. Overnight low temperatures over the weekend will also remain
elevated, especially across the Seattle- Tacoma- Bellevue metro
areas and Cascade Foothills where they will stay in the mid to
upper 60s, providing little relief to the hot daytime conditions.
This will result in widespread areas of Moderate (Orange) HeatRisk
across western Washington, with areas of Major (Red) HeatRisk
across much of the Seattle and Tacoma metro areas as well as the
foothills and valleys of the Cascades. Isolated areas of Extreme
(Purple) HeatRisk are also present in some Cascade valley
locations.

The upper level ridge will weaken slightly on Monday, though the
heat across western Washington will remain firmly in place.
Daytime highs will fall a few degrees across the region, but will
continue to reach the upper 80s to low to mid 90s. While areas
under Major (Red) HeatRisk will decrease slightly, most of western
Washington will remain under Moderate (Orange) HeatRisk. Overnight
lows Monday night will also remain elevated, only bottoming out in
the low to mid 60s for most areas, once again providing little
relief to the hot daytime conditions.

An Extreme Heat Warning remains in effect through Tuesday morning
for the Seattle and Tacoma metro areas and Cascade Foothills and
Valleys for the prolonged heat. Heat Advisories also remain in
effect through Tuesday morning for the remainder of the western
Washington lowlands away from the coast. In addition, fire danger
will reach critical thresholds as a result of hot, dry, and
unstable conditions over the Cascades and eastern Olympics
through the weekend, and a Red Flag Warning has been issued for
these areas (for more details, see the Fire Weather section below).

.LONG TERM /TUESDAY THROUGH FRIDAY/...Warm conditions will persist
well into next week, with highs peaking in the mid to upper 80s
for much of the lowlands through Wednesday. This will
maintain widespread Moderate (Orange) HeatRisk across inland
areas. Weak onshore pushes Tuesday and Wednesday will bring
relief to the immediate coast, but will likely have little impact
on inland areas.

The upper level ridge will begin to break down by the middle of
next week as a trough deepens along the coast. However, ensembles
continue to show uncertainty over how the forecast will evolve
towards the end of next week.

15

&&

.AVIATION...A strong upper-ridge remains in place over the
region throughout the TAF period with light west to southwest flow
aloft. The low level flow is northerly or light offshore. VFR
conditions will prevail areawide throughout the period as well.
Can`t rule out patchy valley fog developing early Saturday morning.

KSEA...VFR throughout the period. Surface winds northerly 8 to 14
knots this afternoon, gradually decreasing overnight. Northerly
winds again 8-12 knots on Saturday.

McMillian

&&

.MARINE...Surface ridging will continue over the coastal waters
as a thermally induced surface low expands northward along the
coast. Breezy northerly to northwesterly winds can be expected at
times over the coastal waters, but will stay under small craft
advisory criteria. The thermal troughing will shift inland early
next week for the return of light onshore flow.

McMillian

&&

.FIRE WEATHER...An upper level ridge and associated surface thermal
trough along the coast will continue to build over the area this
weekend into early next week. Offshore flow will dominate through
the weekend, bringing hot and dry air that will allow for fuels to
rapidly dry out, despite recent rains. Winds may be breezy tonight
into early Saturday morning with wind gusts up to 20-25 mph across
the Cascades. High temperatures this weekend will reach the 80s in
the mountains, 90s across the interior lowlands, approaching 100
degrees in the Cascade valleys. Minimum RH values will drop to 15-
30% in the mountains and the lowlands south of Puget Sound.
Overnight RH recovery will be moderate to poor. Atmospheric
instability will increase through the weekend into early next week.
With all these ingredients, critical fire weather condtiions are
expected over the west slopes of the Cascades and the east slopes of
the Olympics through this weekend. Elevated concerns exist for the
cascade valleys and lowlands around and south of Puget Sound/Hood
Canal. A Red Flag Warning has been issued this afternoon.

Early next week, temperatures will decrease and humidity values will
increase as weak onshore flow attempts to redevelop, sending weak
marine pushes to the Olympic Peninsula. Through the Cascades; hot,
dry, and unstable conditions look to persist at least through
Tuesday. As such, a Fire Weather Watch was issued to address the
lingering fire weather concerns. Periods of offshore flow may
continue to hinder recoveries overnight going into early next week.

Lastly, models are beginning to show signals for some shortwave
troughs moving through the area by mid to late next week. This
additional energy, as well as increasing atmospheric moisture, point
to the potential for isolated thunderstorm chances. Uncertainty is
very high at this point, but wanted to begin to mention the
possibility as we head closer into next week.

62

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...Red Flag Warning from 5 AM Saturday to 9 PM PDT Sunday 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 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 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.

     Extreme Heat Warning until 5 AM PDT Tuesday for City of Seattle-
     Eastside-Lowlands of Pierce and Southern King Counties.

PZ...None.
&&

$$