082
FXUS66 KSEW 080336
AFDSEW

Area Forecast Discussion
National Weather Service Seattle WA
836 PM PDT Tue Oct 7 2025

.SYNOPSIS...Upper level trough moving south along the British
Columbia coast will turn into an upper level low as it reaches the
offshore waters Wednesday afternoon. The low will wobble around
off the Pacific Northwest coast before weakening to a trough and
moving inland Friday night. A cooler upper level low will drop out
of British Columbia and move over the area for the weekend into
the first part of next week. Snow levels down to near 4000 feet
Sunday and Monday with snow in the higher elevations of the
Cascades.

&&

.SHORT TERM /TONIGHT THROUGH FRIDAY/...115. That`s the tally of 70+
degree days in Seattle thus far this year. It`s good enough for
third place behind 2023 (118) and 2015 (116). Will there be another?
If there was a meteorological magic eight ball, the probable answer
would be "My reply is no". The first couple weeks of October in
Seattle are typically a period of significant transition in the
synoptic pattern and this year is proving to be exactly that. The
chance of a 70 degree day in Seattle in the second week of October
is less than half of that of the first. Onshore flow is increasing
this evening ahead of an upper level trough digging southward down
the British Columbia coast. End result: much cooler tomorrow
followed by a several chances for rain heading into the weekend as
an upper low parks offshore and spins several disturbances our way.
Slide those sweaters forward in the closet. It`s fall y`all.

Previous discussion follows with updates to marine and aviation
sections. 27

Satellite imagery shows some high clouds over the northwest corner
of the state otherwise clear skies this afternoon. Temperatures at 4
pm/23z were in the mid 60s to mid 70s with the warmest locations in
the foothills of the Cascades and the Southwest Interior pushing 80
degrees. The 4 pm temperature at Seattle-Tacoma airport was 74
degrees. The 3 warmest October 7ths on record at Sea-Tac have
occurred in the last 3 years. The record 79 degrees was set in 2023.
It was 77 in 2022 and 75 degrees last year. There is a good chance
today is the last 70 plus day of the year for Seattle. Since records
started at Seattle-Tacoma airport in 1945, 75 percent of the 70
degree plus days in October have occurred in the first 10 days of
the month.

Upper level trough currently near Haida Gwaii will continue to
move south tonight and strengthen into an upper level low. By
late Wednesday afternoon the upper level low will be in place off
the Washington coast. First system spinning out of the low moving
over the northern portion of the area late tonight into Wednesday
for a slight chance of rain. Main weather story Wednesday will be
the cooler temperatures. Low level flow turning onshore tonight.
This combined with the approaching low will increase the cloud
cover over the area. High temperatures Wednesday 10-15 degrees
cooler, in the upper 50s to mid 60s. Lows tonight in the 40s.

Upper level low wobbling around off the Pacific Northwest coast
Wednesday night through Friday with the low near the coastline by
late Friday afternoon. Systems spinning out of the low moving
through Western Washington at times through the period. Confidence
not very high in the timing of these features initially with a
lot of variability in the model solutions. There is some consensus
with a system moving over the area Friday afternoon and will have
the highest pops ( likely/categorical ) in that timeframe. High
temperatures in the upper 50s to mid 60s. Brisk low temperatures
in the morning with 40s common and upper 30s in the cooler
locations.

.LONG TERM /SATURDAY THROUGH TUESDAY/...Upper level low weakening
to a trough and moving through Friday night. Another cool upper
level low dropping down out of British Columbia moving over the
area this weekend. This feature will be the coolest air mass the
area has seen since back in the spring with snow levels lowering
down to near 4000 feet in the Cascades. With the low coming from
the north not a lot of moisture initially but enough to produce a
few inches of snow in the higher elevations and even the higher
passes like the North Cascades Highway and White Pass. Persons
heading up into the higher elevations of the Cascades this weekend
should be prepared for snow and cool temperatures.

Like the previous upper level low this one will also just spin
around near the coast Monday and Tuesday keeping cool and showery
weather in the forecast for the first part of next week. Highs by
Monday and Tuesday will likely not get out of the 50s. Felton

&&

.AVIATION...A dry cold front is passing through western WA this
evening, with the front just getting through Puget Sound as of this
evening`s update (winds have begun to switch to the west/northwest
post-front in the major Puget Sound terminals). Onshore flow will
build in behind the front tonight with flow aloft becoming more
southwesterly as a trough digs offshore and along the coast. Most
model solutions (between the HREF and NBM) have MVFR stratus filling
in tonight, although coverage is expected to be most prominent in
the interior (especially after 10-12Z through roughly 18-20Z). The
coast has dipped to MVFR already (likely will be brief in duration).
Only 2 out of 11 HREF members indicate conditions in IFR/LIFR
Wednesday morning (would be more of a ceiling concern). Most likely
will see lower-end MVFR ceilings, with clouds lifting by the
afternoon (will likely not completely clear). Winds will shift to
the southwest 4-8 kt late Wednesday morning.

KSEA...VFR through the evening. With the front through, winds have
turned north this evening and will become light under 5 kt and turn
back to the southwest by around 15Z. MVFR cigs are likely as over
half of the HREF members give MVFR ceilings between 1,000-2,000 ft
between 10-12Z and 18Z Wednesday morning. 2 out of 11 members show
the cigs being lower than MVFR in the morning. NBM also keeps this a
low 10-15% chance of IFR cigs. Winds will pickup out of the
southwest 4-8 kt by late Wednesday morning.

HPR

&&

.MARINE...A weakening frontal system is still on track to
push across the waters this evening, restoring onshore flow over the
waters. In addition, this system will lead to an increase in winds
and wave heights over the coastal waters. Winds will likely approach
SCA strength in the Central Strait of Juan de Fuca tonight (Race
Rocks across the border is up to 28 kt and HREF gave high enough
confidence of at least frequent SCA gusts). As the wave heights
increase over the coastal waters, seas will become steep with wave
heights of 7-12 ft with a dominant period of 7-8 seconds.
Northwesterly winds will increase over the coastal waters as well,
with sustained winds of 20-30 kt possible. The highest wave heights
and strongest winds will be over the outer coastal waters. Seas will
begin to subside starting Wednesday morning below 10 ft and continue
throughout the week.

Additional systems are likely to move over the waters, with guidance
suggesting that a strong system will move over the waters on
Saturday, bringing increased winds and seas. Latest guidance
suggests seas may build up to 15 to 16 ft on Saturday and a chance
(30-45%) of gale gusts are possible through the Strait of Juan de
Fuca.

McMillian/HPR

$$

.FIRE WEATHER...Low level offshore flow weakening this afternoon.
Minimum relative humidity values around 30 percent creating
elevated fire weather conditions this evening in the Cascade foothills.
Increasing onshore flow overnight will allow for decent relative
humidity recoveries Wednesday morning. Minimum relative humidity
values much higher Wednesday with low level onshore flow
continuing. Cooler weather with precipitation chances through the
first part of next week will keep fire weather concerns minimal.
Felton

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...None.
PZ...Small Craft Advisory until 2 PM PDT Wednesday for Coastal Waters
     From Cape Flattery To James Island Out 10 Nm-Coastal Waters
     From James Island To Point Grenville Out 10 Nm-Coastal
     Waters From Point Grenville To Cape Shoalwater Out 10 Nm.

     Small Craft Advisory until 2 PM PDT Wednesday for Coastal Waters
     From Cape Flattery To James Island 10 To 60 Nm-Coastal
     Waters From James Island To Point Grenville 10 To 60 Nm-
     Coastal Waters From Point Grenville To Cape Shoalwater 10
     To 60 Nm.

&&

$$