048
FXUS66 KSEW 161641
AFDSEW

Area Forecast Discussion
National Weather Service Seattle WA
941 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.

&&

.UPDATE...The heat advisory will continue through 10 PM this
evening. Already many areas seeing temperatures in the mid and
upper 70s as of 9 AM this morning, and will continue to see
temperatures reach 80s to low 90s across the region today with
moderate HeatRisk. Changes were made to the aviation, marine, and
fire sections for the morning update.

HPR

&&

.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...Area-wide VFR conditions at all terminals this morning
and are expected to prevail throughout the TAF period. The exception
being KHQM, where IFR/LIFR conditions may return this evening.
Surface winds will become more westerly (5-8 kt) this afternoon,
with northerly/northwesterly surface flow ensuing later this evening
(after ~0z). Breezy conditions expected along the coast with winds
around 8-12 kt.

KSEA...VFR conditions this morning and will prevail throughout the
TAF period. Southwesterly winds this morning will gradually turn
more westerly this afternoon around 7-8 kt. Winds will shift
northeasterly this evening, around 0z-1z, with speeds of 5-7 kt.

Mazurkiewicz/29

&&

.MARINE...A combination of elevated winds and waves is expected for
the outer coastal waters today, for which a Small Craft Advisory has
been issued. An occasional gust up to 30 kt is possible. High
pressure will rebuild over the coastal waters into the weekend.
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 12 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/29

&&

.FIRE WEATHER...Critical fire weather conditions continue in the
Cascades today with dry and unstable conditions in place. Expect
light easterly winds to remain below critical thresholds, but
elevated concerns remain into the adjacent lowlands as dry and
unstable conditions along with light breezes developing. Expect a
shift to westerly winds west and south of Puget Sound this
afternoon, but initial marine push will be shallow so RHs will be
slow to recover again today. Cooling trend will commence later this
week, with a return of cooler and more humid conditions through the
weekend.

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...Red Flag Warning until 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 until 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.

&&

$$