112
FXUS66 KSEW 070347
AFDSEW

Area Forecast Discussion
National Weather Service Seattle WA
847 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 remains over the region with northerly
flow aloft. VFR continues across terminals this evening with winds
out of the north decreasing and becoming light and variable tonight.
Most terminals will see mostly clear skies tonight into Tuesday
morning. There remains 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. Patches of fog in low lying
areas can`t be ruled out (though the threat is much lower). If any
fog 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. Winds will turn more southwest as
a result at 4-8 kt.

KSEA...VFR generally expected through the 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 decreasing this evening - will shift again
northeasterly overnight to 2-5 kt then again towards the WNW on
Tuesday afternoon 4-8 kt.

McMillian/HPR

&&

.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.

&&

$$