956
FXUS66 KSEW 122234
AFDSEW

Area Forecast Discussion
National Weather Service Seattle WA
334 PM PDT Sun Apr 12 2026

.SYNOPSIS...
Weak upper level trough moving through late tonight into Monday
morning. Puget Sound convergence zone developing tonight and
remaining into Monday. Strong front approaching the area
Tuesday moving through Tuesday night. Heavy snow possible in the
Cascades Tuesday night. Cool upper level low behind the front
Wednesday and Wednesday night. Drying northerly flow aloft
behind the low Thursday and Friday. Splitting system arriving
late in the weekend.

&&

.SHORT TERM /TONIGHT THROUGH TUESDAY NIGHT/...
Satellite imagery shows mostly cloudy skies over Western
Washington. Doppler radar has a few showers in the South
Cascades. Temperatures at 3 pm/22z in the lower to mid 50s.

Clouds starting to bubble up late this afternoon but with
plenty of cloud cover will be hard to generate enough surface
heating to create much in the way of shower activity this
evening. Surface gradients turned onshore this afternoon with
onshore flow increasing tonight. A Puget Sound convergence zone
will develop mostly likely over King county tonight with the
convergence zone drifting north early Monday morning. Weak upper
level trough also arriving overnight increasing the shower
chances outside of the convergence zone. Lows in the 40s.

Weak upper level trough moving through Monday morning.
Convergence zone over Snohomish county weakening and moving into
the foothills. Low level onshore keeping skies at least mostly
cloudy. Highs in the lower to mid 50s.

Upper level low and frontal system moving out of the Gulf of
Alaska Monday night into Tuesday morning. Warm front brushing
the north coast late Monday night. Cloud cover will keep lows in
the lower to mid 40s.

Strong cold front approaching Tuesday with the front still
offshore late Tuesday afternoon. Rain starting on the coast in
the morning spreading inland in the afternoon. Winds picking up
along the coast in the afternoon. Cool with highs near 50.

Have issued a winter storm watch beginning late Tuesday
afternoon for the Cascades. Snow level near 3000 feet with heavy
snow possible Tuesday night ahead and with the front.
Breezy/windy conditions developing with the front for the
lowlands. Strongest winds along the coast and over the
Northwest Interior. Felton

&&

.LONG TERM /WEDNESDAY THROUGH SUNDAY/...Cool upper level low
behind the front over Western Washington Wednesday moving east
Wednesday night. Snow levels could get as low as 1500 feet.
Winter storm watch continuing for the Cascades into Wednesday
night for additional significant snow accumulations.

Drying northwesterly flow aloft behind the upper level low
Thursday and Friday. Very cool mornings both Thursday and
Friday with the colder locations getting below freezing. Frost
advisories will likely be needed especially Thursday morning.

Weak upper level ridge moving through Saturday ahead of a
splitting front Sunday.

&&

.AVIATION...
Ceilings have been slow to improve today as MVFR has continue to
linger in the afternoon. A brief spell of VFR cigs are expected to
rebound for terminals along the I-5 corridor. However, MVFR/IFR are
slated to redevelop this evening and maintain tonight area-wide. For
Puget Sound airfields, a convergence zone looks to develop around 03-
06z and may even bring LIFR cigs to KPAE as well. MVFR to areas of
LIFR are forecast to linger into Monday as well.

KSEA...MVFR currently at the terminal as cigs have been slow to
improve. A brief reprieve to VFR is possible between 22z-03z.
However, a models have a PSCZ forming over the airfield with the
return of MVFR/IFR cigs and possible vis reductions. Winds SW this 4
to 8 knots this evening, then increasing to 8-12 kt with gusts up to
20 kt Monday morning. MVFR/IFR cigs are to remain into Monday as
well.

McMillian

&&

.MARINE...
Surface low pressure just off the N CA coast as a high pressure
system develops offshore in the northeastern Pacific. Onshore flow
is increasing as a small craft advisory remains in effect for
westerlies down the Strait of Juan de Fuca this evening and likely
well into Monday. A stronger frontal system arriving late Tuesday
into Wednesday will likely yield more widespread headlines as we
will see increased winds and seas and possible gales through the
strait. Surface high pressure looks to rebuild across the region
towards the second half of the week.

Coastal seas 4 to 6 feet throughout the weekend. Seas will then
start to build upwards to 8 to 10 feet by Tuesday evening and
remaining elevated through Thursday.

McMillian

&&

.HYDROLOGY...
No river flooding the next 7 days.

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...Winter Storm Watch from Tuesday afternoon through late
     Wednesday night for Cascades of Pierce and Lewis Counties-
     Cascades of Snohomish and Northern King Counties-Cascades
     of Southern King County-Cascades of Whatcom and Skagit
     Counties.

PZ...Small Craft Advisory until 6 PM PDT Monday for Central U.S.
     Waters Strait Of Juan De Fuca-East Entrance U.S. Waters
     Strait Of Juan De Fuca.

&&

$$

NWS SEW Office Area Forecast Discussion