659
FXUS66 KSEW 072313
AFDSEW

Area Forecast Discussion
National Weather Service Seattle WA
413 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/...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...VFR conditions expected for most this afternoon and the
evening, but the coast will see ceilings start deteriorating in the
tonight. Cloud cover will continue to increase early Wednesday
morning after 07z, with guidance suggesting that Puget Sound
terminals may see low ceilings as early as 09z-12z. There some
confidence(30-40% chance) that terminals will see cloud decks below
3000 ft. Latest guidance has a 15-30% chance of IFR and even lesser
chance of LIFR. Any lingering clouds will scatter to VFR around
Wednesday afternoon.

KSEA...VFR at the terminal today and tonight. Cloud cover will
increase early Wednesday morning across Puget Sound and guidance
suggests that MVFR ceilings (35% chance) may impact the terminal as
early as 12z. There is a slight chance (10-15%) of IFR. Any
lingering clouds should give way by 19z Wednesday.

Southwesterly winds in the afternoon to 4-6 kt. Winds then shift
more northerly between 00-06z, then shift northeasterly overnight on
Wednesday. Southwesterly flow returns after 13z-14z Wednesday and
remain that way for most the day.

McMillian

&&

.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 may flirt near SCA
criteria through the Strait of Juan de Fuca tonight but confidence is
leaning towards most hours remain sub-criteria. 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

$$

.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.

&&

$$