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FXUS66 KSEW 101559
AFDSEW

Area Forecast Discussion
National Weather Service Seattle WA
859 AM PDT Thu Jul 10 2025

.UPDATE...No changes to the overall forecast. Please see the
aviation and marine sections below for updates to those
forecasts.

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.SYNOPSIS...High pressure will build into the region into the
weekend and through the first half of next week, resulting in
warm and dry conditions across western Washington. The heat is
expected to peak next Wednesday, where temperatures could reach
the low to mid 90s across much of the region.

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.SHORT TERM /TODAY THROUGH SATURDAY/...Post frontal onshore
flow this morning will maintain cloudy skies as light shower
activity tapers off over the North Cascades and along the
northern coast. The marine layer will persist along the coast
throughout the day today but will burn off by the early
afternoon across the interior lowlands, giving way to mostly
sunny skies as high pressure builds offshore. The cloudy skies
will limit high temperatures along the coast today to the mid
60s, with temperatures peaking in the lower 70s further inland.

A weak ridge will pass over the region on Friday, allowing
temperatures to rebound back into the lower 80s across much of the
lowlands. Weakening onshore flow will maintain cloudy skies along
the Pacific coast with mostly clear and dry conditions elsewhere.
Zonal flow will resume over the region on Saturday as a weak
disturbance passes over the periphery of the upper level ridge
building offshore, which will maintain nearly identical conditions
to Friday across western Washington through the weekend.

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.LONG TERM /SATURDAY NIGHT THROUGH WEDNESDAY/...Conditions on Sunday and
Monday will bring more of the same under zonal flow as high
pressure continues to build offshore, with light surface onshore
flow and highs in the low to mid 80s.

A high pressure ridge situated offshore will sharply amplify
during the first half of next week, bringing much warmer
conditions and widespread Moderate (orange) HeatRisk to western
Washington on Tuesday and Wednesday. By Tuesday, the offshore
ridge will sharply amplify and a thermally induced surface trough
is on track to develop along the Pacific Northwest coastline.
Highs will reach the 90s on Tuesday for areas south of the Puget
Sound and along some Cascade Foothill and Valley locations.
Temperatures will continue to increase into Wednesday as the high
pressure offshore continues to build and the thermal trough
shifts northward, with areas across the Puget Sound lowlands on
track to reach the mid 90s. A few daily temperature records may be
broken towards the middle of next week, and a shift to easterly
winds through the Cascade gaps will likely bring elevated fire
weather concerns to the region.

15

&&

.AVIATION...A weak trough is swinging a front across W WA this
morning. The flow aloft will turn more northwesterly today with this
trough. Radar is tracking light showers/drizzle moving eastward. A
smaller band of showers is tracking inland along the coast. These
will be hit and miss around the terminals (given the scattered
nature).

Conditions currently are a mix of VFR/MVFR/IFR. MVFR decks
(expectation is 2,000-3,000 ft bases). A few spots from KPAE to KHQM
may see CIGs drop below 1,000 ft. Mist may drop visibilities at
coastal terminals down to 2 SM. Once the trough clears this
afternoon, a transient ridge will clear up most ceilings (interiors
will see improvement to VFR as early as 21Z, with scattering taking
place this evening. Another push will be possible Friday morning
with lower ceilings as the onshore flow translates down to the
surface.

Southwest winds this morning. These winds will decrease through the
day, and turn northwesterly late this afternoon and evening
regionwide at 4 to 8 kt.

KSEA...Few hit or miss showers possible at the terminal this morning
with MVFR cigs. VFR is favored to return around 20-21z. The chance
for MVFR Friday morning is slightly lower, but a marine push is
expected to push stratus inland from the southwest. Southwest winds
4-8 kt will decrease this morning, and turn northwesterly by 22-00Z.

HPR/McMillian

&&

.MARINE...An occluded front is moving inland this morning with a
passing upper level trough. Some scattered showers are ongoing with
this trough in some of the inland waters, and the coastal waters
will see some showers as well this morning. Additionally, areas of
locally dense fog will be possible again this morning as the front
passes. The coverage is not expected to be widespread enough for a
marine dense fog advisory, but may opt to do a special weather
statement later in the morning if fog does develop. Visibilities
down to a mile are possible, with isolated areas seeing less than a
mile.

The flow over the waters will turn northwesterly later today post
front. Diurnal pushes will continue through the strait (but at this
time do not appear they will reach small craft advisory criteria). A
trough passing to the north early next week may produce gusty winds
in the outer coastal waters, along with steeper seas.

Seas will range 3-4 feet today, increase to 4-6 feet Friday, and
further increase to 6 to 9 feet Sunday through Wednesday, couple
spots further offshore may see 10 feet seas.

HPR/McMillian

&&

.FIRE WEATHER...Cooler and more moist conditions will begin to cease
later today as skies clear and conditions being to warm up with a
weak upper level ridge building over the area. Friday will be the
warmest and driest day of the work week with RH values dropping
back into the 25% to 35% range over the mountains and across the
interior lowlands south of the Puget Sound. More robust onshore
flow will help usher in moist air this weekend despite high
temperatures remaining in the 80s.

While there is some model discrepancy, there is consensus that a
more robust upper level ridge will being to build and move into the
area by the middle of next week. Models are beginning show the
development of a thermal trough along the coast, which would allow
for winds to shift to offshore, promoting much drier and warmer
conditions as well as some potential breezy winds through the
Cascade gaps. This pattern will continue to be closely monitored as
we approach next week.

62

&&


.SEW WATCHES/WARNINGS/ADVISORIES...

WA...None.
PZ...None.

&&

$$