839
FXUS66 KSEW 060340
AFDSEW

Area Forecast Discussion
National Weather Service Seattle WA
840 PM PDT Sun Oct 5 2025

.SYNOPSIS...High pressures will bring dry and mild weather through
early this week. Expect cooler and cloudier weather by midweek
with stronger onshore flow. Low pressure will spin offshore over
the latter half of the week then shift inland over the weekend,
bringing in the best chance for rain in the next 7 days.

&&

.SHORT TERM /TODAY THROUGH TUESDAY/...An upper level ridge will
continue to shift into the Pacific Northwest through Monday and
Tuesday. High temperatures rise a bit each day, reaching the low
to mid 70s on Monday and Tuesday. With mostly clear skies, lows
will remain in the 40s. Some areas around the South Sound may see
lows on Tuesday morning the upper 30s, as areas around the South
Sound reached the upper 30s this morning. Offshore flow will help
to mitigate fog concerns over the next few days, but will allow
for relatively dry relative humidity during the day. See below for
more specifics on fire weather.

.LONG TERM /WEDNESDAY THROUGH SATURDAY/...A weakening frontal
will move through the area Tuesday night into Wednesday. Chances
for precipitation are relatively slim with only a few hundredths
to a trace possible across the area through Wednesday. This system
will help to bring in an upper level trough, allowing winds to
shift back to onshore, as well as usher in cooler temperatures
with highs back in the 60s starting Wednesday. Model consensus is
increasing in the long term forecast. The trough looks to
retrograde a little bit, moving farther offshore Thursday before
sweeping across the area Friday into this weekend. Thursday looks
to be the best chance to have a mostly dry day before more
substantial precipitation chances re-enter the forecast Friday
through the weekend. Cooler air will allow snow levels to drop
over the weekend, potentially as low 5000 ft or lower by Saturday,
which may allow for some mixed precipitation over the passes.

62

&&

.AVIATION...An upper level high building over the area from the
northeastern Pacific will maintain N/NE winds aloft into Monday. VFR
conditions expected to continue throughout the overnight period.
Northerly winds will persist at 7-12 kt for the Puget Sound
terminals into this evening, with a few gusts to 20 kt possible at
times. Meanwhile, winds remain easterly for KHQM and continue to
persist between 7-12 kt. Winds will ease again tonight, likely
around 06Z. A few spots of fog/low stratus may redevelop across
portions of the area on Monday morning, however confidence in
occurrence remains low with easterly winds increasing across the
Cascades tonight and aiding in the drying of the low levels.

KSEA...VFR conditions with winds persisting out of the N/NE at
8-12 kt. Winds will ease again to 6-7 kt tonight around 06Z.
Latest probabilistic guidance continues to highlight roughly a
30% chance of MVFR ceilings returning to the terminal by Monday
morning, however confidence remains low with east winds across the
Cascades and an overall drying trend expected in the low levels.
Have opted to maintain a SCT layer from 14Z-18Z, but confidence is
generally lower as the airmass remains somewhat drier.

14/21

&&

.MARINE...A broad area of high pressure will reside over the
coastal waters, while a thermal trough builds northward along the
coast today into Tuesday. This will result in periods of offshore
flow across portions of the area waters. Seas across the coastal
waters will primarily hover between 3-6 ft into Tuesday. 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 8-11 ft across
the coastal waters. Additional weak systems may move across the
area waters late in the week.

14

&&

.FIRE WEATHER...High pressure over the region will lead to an
offshore pattern Monday through Tuesday, resulting in increased
potential for occasionally breezy winds over the central and
southern Cascades Monday night into Tuesday. Relative humidities are
also expected to decrease into the mid 20%`s Monday afternoon, with
limited recovery Monday night into Tuesday morning. Given the recent
rains, fuel conditions are not approaching critical thresholds, but
elevated concerns will be present Monday into Tuesday due to low
RH`s and breezy winds for zone 659 (central/south Cascades). RH`s
improve midweek through the end of the week with a trough pattern
and the chance of precipitation.

HPR/21

&&

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

&&

$$