920
FXUS66 KSEW 030317
AFDSEW

Area Forecast Discussion
National Weather Service Seattle WA
817 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 FRIDAY/...The current forecast
remains on track with no planned updates tonight. 33

Previous discussion...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 /SATURDAY 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 moisture
continues 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...Southerly  flow aloft continues as an upper level low
retrogrades westward and a ridge beings to build.

VFR conditions this evening with mostly clear skies. Marine stratus
is expected to redevelop this evening and push inland into early
Wednesday morning. IFR to LIFR cigs are expected with periods of
reduced visibility as well. Confidence is highest in stratus making
it into the north interior (PAE, BLI, etc.) but lower in the south
Puget Sound/SEA area. May be intermittent or just for a brief period
at SEA, OLM, and PWT, with a focus on the 14-16Z time frame. Will
continue to have low stratus in the TAF, but confidence is lower.
High clouds may prevent the stratus from going as far inland as it
did this morning. Stratus will quickly retreat to the coast but will
likely linger through much of the day there. HQM may not clear out
at all. Winds remain north/northwesterly across the area through the
TAF period, easing tonight, with winds 5 to 10 kt during the day
Wednesday.

KSEA...VFR through much of the TAF period. Low stratus looks to
encroach upon the terminal vicinity, with the best period of seeing
IFR cigs being most likely in the 13-16Z timeframe. Will likely
continue keeping CIGs in the TAF from 12-17Z for a buffer, but CIGs
may be intermittent at times, especially between 12-14Z. Any CIGs
that develop should be clear by 17Z. North winds 5 to 10 kt through
tonight, easing to 5 kt or less overnight, resuming at 4 to 8 kt
during the day Wednesday.

62

&&

.MARINE...Weak high pressure will remain in place just along the
coastal waters through Thursday. Stratus is expected to redevelop
over the coastal waters. Dense fog may be possible, especially along
the coast and inner waters.

A couple of westerly pushes through the Strait of Juan de Fuca will
occur through the week, the strongest of which is expected Wednesday
night into Thursday with the HREF giving a 40-50% chance of gusts up
to 20 kt Wednesday evening. 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/62

&&

.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.
&&

$$