664
FXUS66 KSEW 210923
AFDSEW

Area Forecast Discussion
National Weather Service Seattle WA
223 AM PDT Thu Aug 21 2025

.SYNOPSIS...High pressure builds into the Pacific Northwest
starting Thursday for a prolonged warming and drying trend. This
leads to widespread Moderate Heat Risk along with elevated fire
weather threat.

&&

.SHORT TERM /TODAY THROUGH SATURDAY/...Strong high pressure over
the West will lead to warm and dry conditions across western WA.
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. Heat
Risk is mostly Moderate for the region and a Heat Advisory is in
effect for a vast portion of western WA. In addition, fire danger
remains elevated due to the warm and dry conditions. Min RHs will
be in the 20s and teens, especially around the south sound and in
the mountains. 33

.LONG TERM /SUNDAY THROUGH WEDNESDAY/...Strong high pressure
stalls over the Pac NW moving into next week. We`ll see more of
the same with temperatures well above normal and in the mid 80s
and 90s. Weak onshore pushes will bring some relief to the coast
but interior temps will remain warm. Probabilities of warm temps
(like greater than 90) start to decrease on Tuesday and more so
on Wednesday, with Moderate Heat Risk coverage shrinking across
western WA. RHs will also be slightly higher with predominately
westerly flow. There are some hints in the models of mid level
moisture pushing northward (high-based showers) but not quite up
to western WA, thus keeping us rain free. 33

&&

.AVIATION...An upper level ridge will continue to build over the
region today with westerly flow aloft. Thermally induced low
pressure expanding northward along the coast will lead to increasing
low level northerly flow...especially through Puget Sound. With the
exception of patchy LIFR stratus along the immediate coast this
morning, VFR conditions will prevail today.

KSEA...VFR. Surface winds N/NE 8 to 12 knots rising to 10 to 15
knots at times this afternoon. 27

&&

.MARINE...Surface ridging in place over the coastal and offshore
waters will gradually weaken toward the weekend as thermally induced
low pressure expands northward along the coast. This will lead to
breezy north to northwest winds across portions of the coastal
waters over the next few afternoons and evenings, but winds should
primarily remain under small craft advisory criteria. The thermal
trough will shift inland early next week with light onshore flow
resuming. 27

&&

.FIRE WEATHER...An upper level ridge building over the area
late this week and into this weekend will bring a warm and
drying trend to western Washington. Periods of offshore flow
will be possible throughout Friday and Saturday, which will help
dry out fuels from recent rains. Elevated fire weather
conditions are expected across portions of the Cascades and
areas south of the Sound into the the weekend with high
temperatures in the upper 80s to low 90s. Minimum RHs will dip
into the 20-30 percent range during the day, with diminished
localized values (teens) possible in the Cascade foothills.
Overnight RH recoveries will be relatively poor 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...Heat Advisory from 11 AM Friday to 5 AM PDT Tuesday for City of
     Seattle-Downtown Everett / Marysville Area-Eastern Kitsap
     County-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-
     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...None.
&&

$$