779
FXUS66 KSEW 161030
AFDSEW

Area Forecast Discussion
National Weather Service Seattle WA
330 AM PDT Wed Jul 16 2025

.SYNOPSIS...One more hot day for the interior today as a thermally
induced surface trough moves inland. The trough will move east of
the Cascades tonight with increasing onshore flow. The weak marine
push tonight and again Thursday night will drop temperatures a
few degrees Thursday and again Friday. Weak upper level trofiness
over the weekend will keep temperatures near normal with areas of
morning low clouds. The low level onshore flow pattern will
continue the first part of next week.

&&

.SHORT TERM /TODAY THROUGH FRIDAY/...Main thought today...it`s
going to hot over the interior. The area is very dry. Let`s be
careful out there and not start any fires.

Satellite imagery shows stratus hugging the Grays Harbor county
coastline with clear skies elsewhere. Easterly surface winds
keeping temperatures near 70 over the Puget Sound area and in the
Cascade foothills at 3 am/109z. Temperatures over the remainder
of the area in the mid 50s to mid 60s.

Today will be the warmest day in the next seven and could be the
warmest day for the rest of the month. Thermally induced surface
trough along the coast will move inland late this morning and into
the Cascades this afternoon. Temperatures aloft peaking with 850
mb temperatures in the plus 17C to plus 20C range. The transition
to onshore flow this afternoon will not be in time for any marine
air to reach the interior. Slightly warmer temperatures aloft,
warmer temperatures to start the day and the lack of afternoon
seabreezes with the flat surface pressure gradients combining to
add around 5 degrees to Tuesday`s highs for most locations. This
puts high temperatures over the interior in the 80s to mid 90s.
The coast will be much cooler with the onshore flow increasing
this afternoon inducing a cooling seabreeze off the Pacific
keeping highs in the 70s.

Thermally induced surface trough moving east of the Cascades this
evening. Onshore gradients peaking this evening with KUIL-KBLI
and KHQM-KSEA around plus 3 mb at 03z. Surface gradients
weakening overnight which will make for only a shallow marine
layer over the interior by early morning. Stratus moving inland
overnight staying west of Puget Sound. The low level onshore flow
and marine air will give the area much cooler low temperatures, in
the 50s and lower 60s. The heat advisory for portions of the
interior will expire at 10 pm tonight.

Zonal flow aloft and weak low level onshore flow Thursday. The
shallow marine layer will retreat back to the coastline in the
morning with sunny skies over all but the coastline by late
morning. High temperatures over the interior 5 to 10 degrees
cooler, in the upper 70s to upper 80s, still well above normal.
Northwesterly seabreezes all day will keep highs near 70 along the
coast.

Weak upper level trough dropping down from the north reaching
Western Washington by Friday afternoon. This feature will be dry.
It will increase the onshore flow across the area resulting in
another 5 to 10 degree cool down from the previous day. Highs in
the interior in the 70s to lower 80s, coast in the mid 60s. Lows
Friday morning in the 50s and lower 60s.

.LONG TERM /SATURDAY THROUGH TUESDAY/...Models in good agreement
over the weekend with an upper level trough to the east,
northwesterly flow aloft and low level onshore flow. Morning low
clouds will give way to plenty of afternoon sunshine for the
interior. The coast will be a little slower to see the sunshine.
Temperatures near normal with highs in the 70s and lows in the
50s.

A little inconsistency creeps into the models for the first part
of next week. There is a general idea of a trough remaining over
the area Monday but there is a lot of variability in the
strength of this feature. Almost a ten degree range in the
ensemble high temperatures. Have gone for the middle ground for
now which puts highs in the upper 60s to mid 70s over the interior
and lower to mid 60s for the coast. More inconsistency Tuesday
with some solutions kicking the trough out to the east while
other solutions leave the trough over the area. Will go with climo
forecast Tuesday with highs mostly in the 70s for the interior
and 60s along the coast. Felton

&&

.AVIATION...Northerly to northwesterly loft aloft as upper level
ridging remains offshore. VFR conditions at all terminals will
continue throughout the TAF period. The exception being KHQM,
where marine stratus may filter into the terminal, bringing
MVFR/IFR conditions through this morning before rebounding back to
VFR. N/NE winds 5 to 10 knots this morning will turn westerly
later this morning lasting throughout the afternoon.

KSEA...VFR conditions this morning will persist throughout the
TAF period. NE winds this morning 5 to 10 knots will gradually
turn westerly throughout the afternoon, generally maintaining the
same speeds.

Mazurkiewicz

&&

.MARINE...Thermally induced trough moving eastward over the coast
this morning will continue to provide increased northerlies over
the coastal waters today. A Small Craft Advisory will continue
over the outer coastal waters today for a combination of elevated
winds and seas. High pressure will then rebuild over the coastal
waters into the weekend, with varying degrees of onshore flow
expected. Diurnally driven westerly pushes down the Strait can be
expected each evening, and may reach Small Craft Advisory strength
at times.

Combined seas 6 to 8 feet will gradually build to 8 to 11 feet
this evening and continuing through Thursday. Seas will then
decease to around 6 to 8 feet by Friday and lessen to 4 to 6 feet
through the weekend.

Mazurkiewicz

&&

.FIRE WEATHER...Widespread elevated fire weather conditions will
continue into Thursday. Warmest and driest conditions today with
minimum relative humidity values in the 20-30% range from about
Seattle south and in the Cascade foothills. Deeper mixed layer
and increased instability over the Cascades with mixing heights
rising today as the thermally induced surface trough moves into
the Cascades this afternoon. The Red Flag warning for Cascade
mountains zones 658 and 659 remains in effect. Today will have the
worst fire weather conditions for existing incidents and the
potential for any new ones if they were to begin. Cooling trend
beginning Thursday with temperatures dropping to near normal
Saturday. Minimum RH values increasing Thursday into the weekend
with the return of low level onshore flow. Fire weather conditions
will remain elevated Thursday with the weak marine push only
providing a shallow layer of marine air. Felton/Bower

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...Red Flag Warning from 11 AM this morning to 11 PM PDT this
     evening for West Slopes of the Central Cascades Generally
     above 1500 Feet-West Slopes of the North Cascades Generally
     above 1500 Feet.

     Heat Advisory until 10 PM PDT this evening for City of Seattle-
     Downtown Everett / Marysville Area-Eastern Kitsap County-
     Eastside-Foothills and Valleys of Central King County-
     Foothills and Valleys of Pierce and Southern King Counties-
     Foothills and Valleys of Snohomish and Northern King
     Counties-Foothills and Valleys of Thurston and Lewis
     Counties-Foothills and Valleys of the North Cascades-
     Lowlands of Lewis and Southern Thurston Counties-Lowlands
     of Pierce and Southern King Counties-Lowlands of Western
     Skagit and Northwestern Snohomish Counties-Lowlands of
     Western Whatcom County-Middle Chehalis River Valley-
     Northern Hood Canal-Olympia and Southern Puget Sound-
     Shoreline / Lynnwood / South Everett Area-Southern Hood
     Canal.

PZ...Small Craft Advisory from 11 AM this morning to 5 AM PDT
     Thursday 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.

&&

$$