Washington State Forecast Discussion

Western Washington


468
FXUS66 KSEW 062151
AFDSEW

Area Forecast Discussion
National Weather Service Seattle WA
251 PM PDT Mon Oct 6 2025

.SYNOPSIS...Dry and warmer conditions will continue across western
Washington through Tuesday with high pressure over the region.
The next upper trough then approaches and arrives around Wednesday,
ushering stronger onshore flow and cooler conditions into the
area. Another disturbance crosses the region into the weekend,
maintaining cooler conditions with precipitation chances and
bringing lowering snow levels for the higher Cascade elevations.

&&

.SHORT TERM /TONIGHT THROUGH WEDNESDAY NIGHT/...Mostly sunny
skies over the region this afternoon with high pressure in
place overhead. Light offshore flow is continuing to spread some
elevated smoke aloft from regional fires across the local area.
Otherwise, no much in the way of weather impacts but
temperatures well into the 60s this afternoon. Expect a few
spots to top out in the 70s, especially from around central
Puget Sound southward and in the Cascade valleys. Not much
change tomorrow with the ridge remaining overhead and
temperatures trending a few degrees warmer, though the offshore
low-level flow begins to ease through the day.

The ridge weakens and shifts eastward Wednesday with the next
disturbance moving into the region. This will knock temperatures
back down into the upper 50s to around 60 degrees and bring
plenty of clouds into the region. Expect some showers to
increase, but rainfall looks rather light along the coast and in
the mountains and even less prominent elsewhere.

&&

.LONG TERM /THURSDAY THROUGH MONDAY/...Ensemble guidance remains
in reasonable agreement with a more active pattern emerging late
in the week and especially over the weekend with a deeper
trough offshore. Some interaction with remnant tropical moisture
from the Pacific may increase precipitation chances at times
Thursday and Friday, but there's not a clear signal for a big
soaking of rain during this time. This begins to shift over the
weekend with guidance clustering around a deeper trough sliding
across the region. This will likely usher in more widespread
precipitation and cooler conditions. With this system, expect to
see snow levels dropping down below 6000 ft and the potential
for some accumulating snowfall in the higher Cascades. Latest
guidance would suggest around a 40% chance of snow at Stevens
Pass (though amounts would generally be rather light below 6000
ft or so) and around a 3-5% chance of snow falling down to
Snoqualmie Pass. Given this, far from a sure thing, but a sign
of the changing season and a good reminder for those who plan to
head to the higher Cascade elevations to remain aware of the
weather and prepared for conditions.

&&

.AVIATION...An upper-ridge over the region is leading to northerly
flow aloft. Subsidence provided by the aforementioned ridge has
brought VFR conditions across W WA this afternoon with the trend
leading into tonight. Mostly clear skies into Tuesday however, there
is a slight chance (20-25%) of IFR to LIFR conditions developing
over fields such as KHQM and KOLM where patchy low clouds and fog
could develop. If manifests, the threat will be short-lived as VFR
conditions are confident to resettle area-wide by 16z Tuesday. Light
low-level offshore flow turning more onshore on Tuesday as well
ahead of an incoming front arriving overnight.


KSEA...VFR at the terminal this afternoon and is expected throughout
the upcoming TAF period. NBM guidance is hinting at fog/low stratus
impacting the airfield after 13z Tuesday, with a 20% chance of LIFR
to IFR developing. If it develops, the activity should subside by
17z-18z at the latest. Northerly winds this afternoon 7-10 kt. Winds
will shift again northeasterly overnight to 2-5 kt then again
towards the WNW on Tuesday afternoon.

McMillian

&&

.MARINE...Currently, a broad area of high pressure over the NE PAC
exists along with a surface thermal trough extending northward along
the West Coast. This has lead to light offshore flow recently
however, a flow reversal is in store. Onshore flow looks to return
on Tuesday as a frontal system draws near. With it, small craft
winds are possible for the coastal waters Tuesday evening into
Wednesday. The latest NBM and HREF probabilities suggest a 50-100%
chance of sustained winds exceeding 21 kt. The highest probabilities
are for the outer coastal waters. Wave heights with this system will
increase to 8-11 ft around this time with the largest waves over the
outer coastal waters. Seas will subside Wednesday afternoon to 5-7
ft and will continue decreasing into Friday to 3-5 ft. Additional
systems may move over the waters late in the week. However, the
latest guidance suggests marine impacts will be minimal at this
time.

McMillian

&&

.FIRE WEATHER...Offshore flow will continue to develop across
western Washington today as high pressure builds over the region.
Elevated fire concerns will be present today into Tuesday due to low
RH values and breezy winds for Zones 658, 659, 652, and the
northwest portion of 661(west slopes WA Cascades and Olympics) but
the recent rains have kept fuel conditions below critical
thresholds. The high pressure ridge will shift eastward overnight
tonight into Tuesday, generating occasionally breezy easterly winds
in the eastern Olympics and through the Cascade gaps tonight into
Tuesday morning. Relative humidity recoveries were poor in the
mountains with locations in the western Olympics diving into the
upper teens at times overnight. Relative humidities are expected to
return to the 20% to 30% range later this afternoon with limited
recovery overnight into Tuesday morning. The wind shift to onshore
westerlies and rising relative humidity will develop from the coast
eastward to the Cascade crest tonight through tomorrow morning.
Relative humidities will continue to improve into next weekend as
chances for precipitation increase.

JBB/15

&&

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

&&