959
FXUS66 KSEW 070325
AFDSEW

Area Forecast Discussion
National Weather Service Seattle WA
825 PM PDT Sat Sep 6 2025

.UPDATE... Scattered showers and thunderstorms continue across W
WA this evening as an upper-level shortwave pushes northward. Most
of the activity has been observed in the southern Cascades and
along the coast into the southwest interior. For tonight, HREF
guidance has elevated convection persisting overnight into
Saturday morning, pushing off the Cascades and inching towards the
lowlands but gradually waning in intensity into Sunday morning.
Overnight lows will fall to the mid 50s to near 60 F. The previous
discussion is below along with an updated aviation section:


&&


.SYNOPSIS...An upper level trough will remain offshore through the
weekend before shifting inland early next week, maintaining cooler
and unsettled conditions with chances for showers and
thunderstorms across western Washington. A brief period of drier
conditions is possible towards the latter half of next week, with
a return of showers by next weekend.



&&

.SHORT TERM /TONIGHT THROUGH TUESDAY/...A deep upper level low
continues to churn offshore today as a series of shortwaves in the
southerly flow aloft stir up shower and thunderstorm activity
across the region. The ripple that brought showers and
thunderstorms to the south Puget Sound this morning will continue
to exit to the north this afternoon with lingering light showers
progressing to the northwest. The next, slightly stronger
shortwave will continue to move northward over central Oregon this
afternoon, reaching Washington by this evening. The greatest
potential for thunderstorm activity remains over the Cascades,
where ensembles maintain a moderate (30% to 40%) chance of
thunderstorms. The main threat of these storms will be frequent
lightning, accompanied by outflow wind gusts up to 30-35 mph.
However, models continue to show a large amount of uncertainty
over the exact placement and coverage of thunderstorms that may
develop later this afternoon and evening with a 10% to 30% chance
across the lowlands. Thunderstorms are favored to develop over the
Cascades and foothills, and may drift north to northwest over the
lowlands later this evening, but confidence is low. Wildfire
smoke and cloud cover continue to complicate convection, which may
prove to be limiting factors. Temperatures are on track to reach
the mid 70s across much of the lowlands and in the 60s along the
coast.

Another ripple in the southerly flow aloft will move over western
Washington overnight into Sunday morning, maintaining the chance
for nocturnal convection. High resolution forecast models continue
to show vast differences over the coverage and intensity of any
overnight activity that may develop, but the best chances for
convection once again look to be over the Cascades. Temperatures
will cool several degrees on Sunday, peaking in the 60s to near 70
degrees for most areas.

The upper level trough will move inland over Oregon on Monday and
Tuesday, with continued chances for showers and isolated
thunderstorms primarily over the mountains. As the trough weakens,
chances for precipitation will slowly diminish and high pressure
will begin to build along the coast. Cooler and cloudy conditions
will continue across western Washington, with highs staying in the
60s to low 70s.

.LONG TERM /WEDNESDAY THROUGH SATURDAY/...Forecast confidence
decreases heading into the long term, though most operational
models show upper level ridging building along the coast during
the latter half of next week. This would allow for a brief period
of drier conditions and a return to near-normal temperatures.
Ensembles show unsettled conditions returning by next weekend,
with potential for more precipitation across the region as early
as next Friday.

15


&&


.AVIATION...An upper ridge axis over the Northern Rockies and
a broad upper trough offshore continue to promote south to southeast
flow aloft over Western Washington. Light low level onshore flow
continues near the surface. Widespread wildfire smoke and haze aloft
will persist across the region. An upper level disturbance has lead
to thunderstorm activity observed along the Cascades and the
southwest interior of W WA. Some of this could impact area terminals
along the I-5 corridor as the night progress. Coastal stratus will
spread inland once again tonight with widespread LIFR or IFR
ceilings expected west of the Cascades on Sunday morning.

KSEA...Hazy conditions with varying amounts of mid and high level
clouds are expected to continue into this evening. Concern for a
renewed threat of thunder remains and current thinking now favors
later this evening...in the 04Z to 08Z window. LIFR/IFR stratus is
expected to return to the terminal 09Z-12Z Sunday morning. Surface
winds S/SW 5 to 7 knots...except locally gusty and erratic around
any thunderstorms.

27/McMillian


&&


.MARINE...A weak surface ridge over the coastal and offshore waters
will be replaced by a weak low on Sunday. This general pattern will
persist early next week before a stronger surface ridge rebuilds
offshore around the middle of next week.  27


&&

.FIRE WEATHER...The next round of thunderstorms will likely
develop and move into the region from the south or southeast this
afternoon and evening, with around a 30-40% chance of
thunderstorms near the Cascades, and still a 15-20% chance across
nearly all of western Washington. This threat will linger Sunday
as additional disturbances push up and across the region,
especially for the Cascades. The main hazards with these
thunderstorms are gusty erratic winds, brief heavy downpours, and
frequent lightning. That said, confidence in sufficient coverage
to warrant critical conditions and associated fire weather
headlines remains low. Expect a lull on Monday, but another
disturbance Tuesday will bring another round of showers and
Cascade thunderstorm chances. That said, the continued trend of
cooler and cloudier conditions and increased moisture should
continue to bring a lowering trend with respect to expected fire
weather impacts as the next week progresses.

Cullen


.SEW WATCHES/WARNINGS/ADVISORIES...
WA...None.
PZ...Small Craft Advisory until 3 AM PDT Sunday for Central U.S.
     Waters Strait Of Juan De Fuca-East Entrance U.S. Waters
     Strait Of Juan De Fuca.

&&

$$