512
FXUS66 KSEW 040322
AFDSEW

Area Forecast Discussion
National Weather Service Seattle WA
822 PM PDT Wed Sep 3 2025

.SYNOPSIS...High pressure will continue over the region through
midweek. This will continue to bring above normal temperatures to
the region and Moderate to Major HeatRisk to the Cascade valleys,
as well as critical to elevated fire weather conditions in the
mountains. Monsoonal moisture may bring isolated shower or
thunderstorms chances late in the week. Cooler temperatures look
to arrive this weekend and into the first part of next week.

&&

.SHORT TERM /TONIGHT THROUGH SATURDAY/...One more hot day for the
Cascade foothills and valleys on Thursday with highs in the 80s
and 90s. Meanwhile, critical fire weather thresholds will be met
over the Cascades for hot, dry and unstable conditions. There`s a
lot of wildfire smoke over western WA with moderate air quality
over much in the interior. 33

Previous discussion...Upper level ridging continues to build over
western Washington this afternoon with high clouds streaming in
from the south. Areas of haze will also be apparent this evening
from ongoing wildfires across the area. High temperatures this
afternoon staying in the upper 70s into lower 80s for most
interior areas, with areas in the Cascade valleys seeing temps in
the upper 80s into the lower 90s. A heat advisory continues -
mainly for the Cascade valleys until Thursday evening.

Ridging will start to move eastward on Thursday, with light
onshore flow allowing marine stratus to filter through some of the
interior. Stratus will burn back rather quickly for another day of
warm and dry conditions. High temperatures will be a touch cooler,
with some more high clouds streaming in overhead. Temps will
remain in the low 80s for interior locations, with Cascade valleys
seeing temps in the upper 80s. Areas along the water will see
temps in the upper 60s.

The ridge axis will drift more eastward on Friday allowing a upper
level low to slowly drop down from the Gulf of Alaska with flow
turning southerly. A weak disturbance could bring chance showers
mainly in the south Cascades Friday evening but will keep the
mention of showers for most of the region, with mostly dry
conditions expected.

Upper level troughing will remain offshore with ensembles
highlighting potential monsoon moisture entering our area. Models
have indicated a slight chance (15-20%) for an isolated o
thunderstorm or two, mainly in the Cascades and in the Olympics.
The details of this is still uncertain, with guidance struggling
with path and track of the low. Elsewhere, it seems that chances
of some isolated showers are also possible. High temperatures will
cool down some, with highs in the mid 70s across the interior and
mid 60s for areas along the water.

.LONG TERM /SUNDAY THROUGH WEDNESDAY/...Confidence is not
particularly high in the long term, but ensembles seem to suggest
upper level troughing continuing to influence western Washington,
with cooler temperatures and perhaps more chances for rain on the
way. High temperatures may struggle to even reach 70 degrees by
Tuesday/Wednesday, with perhaps a sign that fall weather is
is on it`s way?

Mazurkiewicz

&&

.AVIATION...S/SE flow aloft with a ridge off to the east and a
shortwave trough moving up through it. Mostly VFR conditions this
evening except along the coast, with high clouds spreading northward
across the area. Quite a bit of smoke throughout the atmosphere form
area fires are and will continue to limit slant-wise visibility.
Stratus along the coast will continue to lower and move inland
tonight. With slightly stronger onshore pressure gradients, expect
the stratus to make it farther inland, close to OLM in the southwest
interior and through much of the Strait of Juan de Fuca and into
portions of the northwest interior. Low (10-15%) chance that the
stratus makes it into the Seattle metro. High clouds overhead for
most of tonight should eliminate the risk of fog in areas not under
marine stratus. Rapid retreat of the stratus to the coast is
expected again Thursday morning for mostly VFR conditions. Winds
become light tonight, then northerly tomorrow.

KSEA...VFR through the TAF period with high clouds for much of
tonight and tomorrow morning. Hazy. Low (10-15%) chance of marine
stratus making it to the terminal; should remain to the west. Winds
becoming light overnight, with northerly winds 4 to 8 kt tomorrow.

62

&&

.MARINE...Broad and weak high pressure will persist over the coastal
waters through Saturday, keeping northwesterly winds in the forecast
though slowly easing. A low pressure system looks to slowly move
through the waters Sunday night into Monday, turning winds more west
to southwest.

Persistent stratus will continue to lower, causing limited visibility,
especially along the inner coastal waters, where a dense fog
advisory remains in effect though late Thursday morning. Winds
through the Strait are at around 15-20 kt with a few gusts up to 20-
25 kt, so the low-end Small Craft Advisory will remain in effect
through tonight.

Seas of 4-6 ft will continue through Friday, dropping to 3-4 ft this
weekend into early next week.

62

&&

.FIRE WEATHER...Hot and dry conditions continuing into Friday.
Shallow marine layer in the late night and morning will continue to
give excellent RH recoveries in the lowlands. But, with the layer
being shallow RH recovery will be poor in the mid-slopes and ridges
in the Cascades and Olympics through Friday. The poor recoveries,
very dry conditions and increasing instability will keep the Red
Flag Warning for fire weather zones 658 and 659 in effect through
Thursday evening. Cooler conditions over the weekend with a deeper
marine layer will bring about an end to the threat. There is a
chance of showers over the weekend with possible thunderstorms over
the Cascades Saturday afternoon and evening but confidence remains
low with exact coverage and intensity.

McMillian

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...Red Flag Warning until 9 PM PDT Thursday for West Slopes of the
     Central Cascades Generally above 1500 Feet-West Slopes of
     the North Cascades Generally above 1500 Feet.

     Heat Advisory until 5 PM PDT Thursday for 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.

PZ...Dense Fog Advisory until 11 AM PDT Thursday 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-
     Grays Harbor Bar.

     Small Craft Advisory until 5 AM PDT Thursday for Central U.S.
     Waters Strait Of Juan De Fuca-East Entrance U.S. Waters
     Strait Of Juan De Fuca.

&&

$$