301
FXUS66 KSEW 061721
AFDSEW

Area Forecast Discussion
National Weather Service Seattle WA
1021 AM 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,
maintaining cooler conditions with precipitation chances and
light snow over the higher Cascade elevations.

&&

.SHORT TERM /TODAY THROUGH WEDNESDAY/...High pressure will
continue to build into the region today, bringing warmer
conditions and another day of sunshine across western Washington.
Offshore flow will help to mitigate fog development early this
morning, with temperatures across the lowlands peaking in the
upper 60s and lower 70s later today. Clear skies later tonight
will allow temperatures to dip into the 40s for most areas, and
continued offshore flow will help limit the potential for morning
fog to develop.

The upper ridge axis will shift east of the Cascades by Tuesday as
a trough deepens over the Gulf of Alaska. As southwest flow
develops aloft, easterly winds will increase through the Cascade
gaps early Tuesday morning. Temperatures Tuesday will peak a few
degrees higher than today, with most areas south and east of the
Puget Sound reaching the mid 70s.

A frontal system will split as it reaches the coast early
Wednesday, with a cutoff low projected to develop along the
Pacific Coast by the middle of the week. This introduces a return
to onshore flow alongside chances for light rain showers on
Wednesday, mainly confined to the northern coast. However, rainfall
amounts will likely not exceed a trace. As the low deepens
offshore, wrap around moisture may make its way northward later on
Wednesday to generate additional showers over the Cascades.
Temperatures will cool considerably on Wednesday, with highs
barely making it into the 60s across the lowlands.

.LONG TERM /THURSDAY THROUGH SUNDAY/...Forecast models show good
agreement over a deepening low pressure system traversing
southward along the Pacific Coast through the rest of the week,
maintaining chances for light shower activity from moisture
advected northward. Temperatures will remain slightly below normal
as troughing persists over the region, with highs in the low 60s
Thursday and Friday. The best chance for more widespread rainfall
will enter the region over the weekend as another trough swings
across the area. Temperatures will peak in the mid to upper 50s
across western Washington, with snow levels predicted to fall
as low as 4000-4500 feet. While liquid amounts are on track to be
generally light, this may produce the first dusting of snow over
the Cascades for the season, with a light dusting possible through
Snoqualmie Pass over the weekend.

15

&&

.AVIATION...VFR across all terminals so far this morning. Some
patchy river valley fog is evident over the Snoqualmie and
Chehalis valleys but so far has evaded the TAF sites. Otherwise,
VFR conditions expected to persist for the majority of the TAF
period, although guidance suggests fog/low stratus is possible
near the end of the TAF period, after 11z Tuesday. Light/calm to
northerly winds at 4-6 kt increasing this afternoon to 5-10 kt.


KSEA...VFR at the terminal this morning and is expected to persist
for the majority of the TAF period with high clouds at times.
Guidance is hinting that fog/low stratus may return after 13z
Tuesday, with a 25% chance of IFR and 20% chance of LIFR.
Northeasterly winds this morning at 6-8 kt will become northwesterly
in the afternoon at 7-10 kt. Winds will shift again northeasterly in
the evening after 3z to 5-8 kt.

29/McMillian

&&

.MARINE...Broad high pressure will persist over the coastal waters
today and weaken Tuesday morning. In addition, a thermal trough
along the coast will bring periods of offshore flow at times.
Surface flow will then shift onshore as a frontal system moves over
area waters Tuesday evening into Wednesday. This will lead to
increased winds and wave heights for the coastal waters. Latest
guidance suggests small craft winds are possible for the coastal
waters. The latest probabilities suggest a 45-80% chance of
sustained winds exceeding 21 kt, while there`s a 40-90% chance of
gusts exceeding 21 kt. The highest probabilities are for the outer
coastal waters. Wave heights with this system will increase to 8-11
ft. 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.

29

&&

.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.

&&

$$