985
FXUS66 KSEW 162249
AFDSEW

Area Forecast Discussion
National Weather Service Seattle WA
349 PM PDT Wed Jul 16 2025

.SYNOPSIS...Hot and dry conditions will continue this afternoon
across western Washington as a surface thermal trough moves inland
past the Cascades by tonight. Behind this trough, onshore flow
will increase through the rest of the week, resulting in a drop of
temperatures through the weekend into early next week with more
clouds. An upper level low will bring a slight chance of showers
over the Cascades Monday and Tuesday.

&&

.SHORT TERM /TONIGHT THROUGH SATURDAY/...A surface thermal trough
has moved inland this afternoon, and will continue to push east
going into tonight/Thursday. This has been the main driver of the
heat the past two days as warm air gets induced into the region.
Temperatures this afternoon have peaked in the upper 80s to mid
90s, with the warmest temperatures in the south interior.

The biggest question of the heat going into tomorrow is how much
relief will be provided the return of onshore flow into the
region. The HREF ensembles members have winds beginning to
increase out of the southwest tonight/Thursday morning along the
coast, which will cool temperatures along the Pacific back to near
normal. The winds in most ensemble members struggle to get any
breeze past Olympia Thursday until the evening timeframe. Areas
that do get wind (Olympia/Chehalis Valley and areas northwest)
will see cooler temperatures tonight with lows in the low 50s. The
more urban areas (Tacoma northward up to Bellingham) will see mid
and upper 50s for lows tonight (and a few low 60s in the Seattle
metro).

Highs will still be warm (but a few degrees cooler compared to
Wednesday), with highs reaching the low to upper 80s in interior
areas. The previously mentioned areas getting the onshore
seabreeze will see lower HeatRisk impacts (only minor), while
interior areas not receiving wind will continue to see moderate
HeatRisk impacts until the seabreeze arrives Thursday evening.
Have elected to extend the heat advisory from Tacoma up to
Bellingham (including Cascade Foothills) through 5 PM PDT Thursday
due to the moderate HeatRisk/warmer overnight temperatures, and
lack of a breeze.

The onshore flow will continue to reduce temperatures Friday and
Saturday as the onshore flow/northwest flow aloft increases. A
trough does pass through Friday into Saturday with a cool front,
but no precipitation is expected (just an increase of clouds
Friday afternoon into Saturday). High temperatures in interior
areas Friday will range from 70s to low 80s, and this drops to the
low to mid 70s Saturday.

Additionally, some haze/smoke from fires in western WA will be
present (but generally light in coverage near surface and aloft).

.LONG TERM /SUNDAY THROUGH WEDNESDAY/...The cool pattern continues
through the weekend into early next week with highs remaining
steady in the 70s. There is a warming trend in the ensembles going
towards midweek, but this is not expected to produce heat impacts
at this time. Sky coverage will be a mix of clouds and sun, with a
few mornings seeing increase cloud coverage from marine pushes.
There is a slight chance of showers in the Cascades Monday/Tuesday
with a trough/front passing through.

HPR

&&

.AVIATION...VFR conditions expected to persist this afternoon and
evening. Majority of terminals will remain VFR overnight, but
guidance hints at the potential for lowered ceilings to return
overnight with the marine low-stratus pushing inland. There is
uncertainty regarding how far east the low-stratus will be. At this
time, there is high confidence that terminals along the coast will
go down IFR/LIFR. With a 30%-40% chance of MVFR ceilings along the
Kitsap Peninsula and southern interior (KOLM). Improvement is
expected by the afternoon after 16z-18z for inland terminals and 20z-
21z along the coast.

Southwesterly winds will shift more westerly/northwesterly this
evening. Southwesterly winds return overnight.

KSEA...VFR conditions expected to persist throughout the TAF period.
With the latest guidance, the marine stratus is not expected to make
it to the terminal. Current probabilities of MVFR ceilings are
around 20%-30%. Southwest winds will become more westerly around 0z.
Winds will shift northwesterly around 1z-2z, with speeds of 6-8 kt,
easing to 3-4 kt after 6z. Southwesterly winds return overnight
after 12z-13z.

29

&&

.MARINE...Elevated winds and waves this evening through Thursday
morning along the outer coastal waters, with an occasional gust of
30 kt possible. A Small Craft Advisory remains in effect through
early Thursday morning. Surface high pressure will remain situated
west of area waters, keeping northwesterly flow over the coastal
waters. On Thursday, a low pressure system will move over the
coastal waters, with a front stalling near the Washington/British
Columbia border. The front will move over the waters early Friday
morning, bringing sustained wind speeds to around 21 kt for the
outer coastal waters. High pressure will rebuild over the waters
Friday evening and persist into the weekend. High pressure will
weaken early next week. Westerly pushes along the Strait of Juan de
Fuca will occur each evening. The next push that looks to approach
small craft criteria is Friday evening, with current probabilities
at 60%-70% of 21 kt or greater.

Seas will continue building today to 6-11 ft, with the highest wave
heights in the coastal waters. Seas will gradually subside
throughout the day on Thursday and Friday. Seas look to remain below
3-5 ft into the weekend and next week.

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.

&&

$$