710
FXUS66 KSEW 050325
AFDSEW

Area Forecast Discussion
National Weather Service Seattle WA
825 PM PDT Sat Oct 4 2025

.SYNOPSIS...Skies will become mostly clear tonight as upper level
ridging begins to build over the area behind an exiting shortwave
trough. This will allow for more clear skies as well as warmer
temperatures and lower humidity through Tuesday. Cooler and wetter
conditions look to return Wednesday through the latter half of
the week, but details remain uncertain.


&&

.SHORT TERM /TONIGHT THROUGH TUESDAY/...No major changes have been
made to the forecast this evening. The aviation section has been
updated, but the rest of the previous discussion can be found
below.

Clouds should continue to decrease in coverage this evening as
upper level ridging begins to nose into the region as a trough
continues to slide to the southwest. With the decreased cloud
coverage, expect areas of low stratus to from through portions of
the area. Since low level winds will begin to turn offshore,
thinking that fog will be less likely as the offshore winds will
help to dry out the lowest levels. Forecasted low temperatures
will remain cool, in the 40s across most of the area. Freezing
levels will dip to around 4500-5000 ft across the North Cascades
allow for subfreezing temperatures around Washington Pass.

Upper level ridging will continue to move over the area through
Tuesday. This will allow temperatures to slowly warm each day.
High Sunday will be in the mid 60s across the area, rising to the
low to mid 70s on Tuesday. This will also allow minimum RH values
to dip below 40% across the entire region, with some areas
reaching below 30%, particularly across the central and southern
WA Cascades. Additionally, offshore flow will continue through
Tuesday with a thermal trough developing along the coast. Winds
may reach up to 15-20 mph over the Cascades from Monday night into
Tuesday morning. While this is not critical fire weather
conditions, active fires may see an uptick in activity with a
notable change in the wind direction.

.LONG TERM /WEDNESDAY THROUGH SATURDAY/...Model solutions are
starting to look more consistent on Wednesday, bringing the
trough into the region from the northwest. However, precipitation
amounts will be meager with most of the area receiving, at most,
a few tenths of an inch with still a solid percentage of ensemble
members keeping things mostly dry. As for where the trough goes
Thursday and beyond, things remain very uncertain. Some keep the
trough directly overhead, some (including the GFS) have the low
retrograde back over the Pacific, while a few progress the trough
through intermountain west. Ensemble cluster analysis reveals that
most ensemble members keep upper level troughing in place,
through about 10% actually start to reintroduce another ridge.
That being said, the mean solution keeps temperatures seasonable
(highs in the mid to upper 60s, lows in the 40s) with chances for
rain and showers from Wednesday through next weekend.

62


&&

.AVIATION...Northerly flow will continue aloft through the TAF
period. Winds primarily persist out of the north between 4-8 kt.
Some lower cigs are possible through the Strait of Juan de Fuca,
and portions of Puget Sound late tonight into early tomorrow
morning. Winds will ease somewhat overnight, before shifting more
NE and increasing to 7-12 kt again between 14-18Z. Ceilings will
lower towards MVFR again overnight, likely between 12-15Z, with
improvement towards VFR expected again by 18-21Z.

KSEA...VFR at the terminal this evening, with cigs above 5000 ft.
Winds are northerly, and will persist through the overnight hours,
becoming more northeasterly after 09Z. Guidance is suggestive of
MVFR cigs between 09Z-15Z (30-35%), and around 15-20% likelihoods
of IFR conditions. Winds are expected to increase out of the north
between 14Z-18Z, and there could be overlap of some lower cigs in
that period. A return to VFR cigs seems more likely after 18Z with
north winds continuing.

62/21

&&

.MARINE...A weak frontal system will continue to make its way across
the region tonight, with no significant impacts expected across
the area waters. A broad area of high pressure will then build
back across the coastal waters in its wake, while a thermal trough
builds northward along the coast Sunday through Tuesday. Onshore
flow will switch to offshore across the area waters as a result.
Seas across the coastal waters will primarily hover between 3-6
ft. A weakening frontal system will then move over the area waters
on Tuesday, allowing for winds to switch back to onshore. A push
of westerly winds is likely down the central and east Strait of
Juan de Fuca Tuesday evening in its wake, with seas building to
8-10 ft across the coastal waters. Additional weak systems may
move across the area waters late in the week.

14


&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...None.
PZ...None.
&&

$$