700
FXUS66 KSEW 022218
AFDSEW

Area Forecast Discussion
National Weather Service Seattle WA
318 PM PDT Tue Sep 2 2025

.SYNOPSIS...High pressure will continue to build over the
region, maintaining warmer and dry conditions across Western
Washington through midweek. This will bring above normal
temperatures to the region and Moderate to Major HeatRisk to the
Cascade valleys, as well as elevated to critical fire weather
conditions in the mountains. Monsoonal moisture may bring
isolated shower or thunderstorms chances late in the week, with
a cooler pattern likely arriving into the weekend.

&&

.SHORT TERM /TONIGHT THROUGH THURSDAY NIGHT/...As expected, the
lingering stratus has cleared across the region this afternoon.
While temperatures continue to climb through the lower to mid
70s across most of the interior, it`s worth noting the very warm
conditions evident across some of the higher elevations of the
Olympics and Cascades, as well as in the Cascade valleys, with
temperatures in the upper 70s to upper 80s in the higher
elevations. Expect Moderate to local Major HeatRisk due to the
combination of hot days and mild nights for the Cascade valleys,
with the heat advisory continuing for these areas as a result.
Dry and unstable conditions will lead to critical fire weather
conditions in the Cascades as well, with more details in the
Fire Weather section below.

An embedded disturbance will bring some relief and a deeper push
of clouds on Thursday to much of the area, though some of this
relief may be more limited in portions of the Cascades. This
may spread additional moisture north into western Washington to
even support an isolated thunderstorm into the region, though
this potential is low (less than 15 percent) and continues to
decrease.

&&

.LONG TERM /FRIDAY THROUGH TUESDAY/...Ensemble guidance
continues to suggest a shift in the pattern late in the week
with a broad upper trough emerging over the northeastern Pacific
basin. This should bring a return of near to below-normal
temperatures and increasing cloud cover and precipitation
chances through the start of next week. As this mosrcontinues
to increase, will see rain chances increase a bit as various
disturbances rotate through the region. However, confidence in
pinpointing timing and location of these features remains quite
low at this time.

&&

.AVIATION...An upper level low will continue to retrograde
northwestward through the day, with a weak high/ridge tilting
northwestward over the region into B.C. tonight/Thursday. The flow
is very weak aloft, but will turn more from southerly to
southeasterly. Down at the surface, weak high pressure remains over
southwest B.C. with a surface trough to the east.

VFR conditions will continue this afternoon (with a few low cloud
areas remaining in the west Strait of Juan de Fuca area). Some haze
aloft has been observed due to wildfire smoke. Another marine push
is expected to bring stratus inland up to the interior Wednesday
morning. For the interior: 30-40% chance of MVFR CIGs, with a 20-30%
chance of IFR, and a 10-15% chance of LIFR. West of the
interior/Puget Sound, chance of IFR is around a 60-80% (90% along
the coast), and a 30-50% chance of LIFR. The chance of low VIS is
less than 20% for less than 5 mi in the interior, but much higher
along the coast (30-50% less than 1 mi). Low CIGs/VIS will clear
late Wednesday morning into the early afternoon. North winds 5 to 10
kt (couple gusts to 15 kt possible along the waters) today will
decrease down to 4 to 8 kt tonight, and increase to 5 to 10 kt
Wednesday.

KSEA...VFR through tonight, with lower CIGs likely Wednesday morning
(20% chance it`s down to IFR and 10-15% chance of LIFR). Will become
VFR late Wednesday morning/afternoon. Winds out of the north 5 to 10
kt through tonight, likely decreasing to under 5 kt and increasing
to 4 to 8 kt Wednesday.

HPR

&&

.MARINE...Weak high pressure will remain in place just along the
coastal waters through Thursday. With weak flow/onshore flow, there
is an increased chance of low fog along the coastal waters and
portions of the Strait of Juan de Fuca Wednesday morning, with
around a 40% chance of these areas seeing visibilities tonight less
than 1 mi. A couple of westerly pushes through the Strait of Juan de
Fuca will occur this week, the strongest of which is expected
Wednesday night into Thursday with the HREF giving a 50% chance of
sustained winds exceeding 20 kt. The high will then weaken Friday
and Saturday with a low pressure system moving into the offshore
waters. A separate surface trough will remain east of the Cascades
through the weekend.

3-4 ft seas tonight will bump to 4-6 ft Wednesday into Friday,
decreasing back to 3-4 ft through the weekend into next week.

HPR

&&

.FIRE WEATHER...Continued warmer and drier conditions will
develop through Wednesday under high pressure. While marine
influence will continue to provide for excellent RH recoveries
in the lowlands, expect to see continued poor recoveries in the
mid-slopes and ridges in the Cascades (as well as the Olympics
today). With this continued concern for poor recoveries, very
dry conditions Wednesday, and increasing instability, have
upgraded to a Red Flag Warning for Wednesday for fire weather
zones 658 and 659. This will be the primary fire weather concern
for the week, with a return to cooler conditions with a deeper
marine layer later in the week. There is the potential for some
monsoonal moisture to arrive and perhaps lead to a few isolated
showers or thunderstorms late in the week, but confidence
remains low with respect to the specifics.

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...Red Flag Warning from noon to 9 PM PDT Wednesday 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...None.

&&

$$