422
FXUS66 KSEW 200907
AFDSEW

Area Forecast Discussion
National Weather Service Seattle WA
207 AM PDT Sun Apr 20 2025

.SYNOPSIS...A trough will bring widespread rain to Western
Washington Sunday. Post trough convergence zone may lead to
additional inches of snow along the passes Sunday evening.
Conditions will begin to dry out on Monday. High pressure will
bring dry and warmer conditions through midweek. Precipitation
chances return late in the week.

&&

.SHORT TERM /TODAY THROUGH TUESDAY/...Onshore flow will persist
today and showers will increase with a passing trough axis. Most
of the showers will be along the coast and mountains, with the
focus shifting to the central sound and Cascades this
afternoon and evening as a Puget Sound Convergence Zone develops.
Snow levels will start around 4000 ft and will lower to around
2500 ft overnight with a few inches of snow expected at both
Stevens and Snoqualmie Pass.

Monday will be drier (for the lowlands) but also cooler under NW
flow. Forecast highs are in the 50s with lows Monday night in the
30s to lower 40s. Areas around the south sound may see freezing
temps with lows in the lower 30s possible.

Dry N/NW flow continues into Tuesday with a ridge centered
offshore. Expect mostly sunny conditions with highs in the
interior around 60. The coast will be cooler and in the 50s with
onshore winds. 33

.LONG TERM /WEDNESDAY THROUGH SATURDAY/...High pressure brings dry
and slightly warmer weather moving forward through Wednesday and
Thursday. Highs on Thursday will peak in the lower 70s in the
interior, with 60s at the coast. The ridge axis shifts east
Thursday night and Friday while a trough digs offshore. This
trough will tap into moisture for a chance of showers and cooler
conditions overall. An upper level low will spin overhead on
Saturday for additional showers and ongoing cooler conditions. 33

&&

.AVIATION...An upper level trough will move through western WA
today, turning and increasing the flow aloft to northwest later
today. Remnants of yesterday`s cold front remains east of the
Cascades as a surface trough. Showers continue around the vicinity
of terminals this morning (north of I-90 and along the coast), with
activity expected to expand throughout most terminals today. No
major impacts are expected with the showers, except for a likely
convergence zone late Sunday into Monday that may cause sporadic
shifts in winds to the north/east from 23Z-05Z (most likely area for
setup is King/Pierce Counties). Ceilings will remain a mix between
MVFR/VFR, with VFR coverage increasing after 21Z through Monday
morning. Most terminals will see southwest winds at 5 to 10 kt this
morning, turning more westerly late Sunday (outside of the
convergence zone). Gusts to 20-25 kt will be possible for terminals
along the Strait of Juan de Fuca Sunday evening.

KSEA...Vicinity showers this morning to the northeast with MVFR
ceilings expected to drop to as low as 1,500 feet by mid morning
before improving to VFR around 21Z with broken or overcast skies.
South winds in the morning 5-10 kt. Additional showers are expected
to pass through today, and a convergence zone will develop close or
over the terminal between 00Z-12Z Monday. Wind shifts to the
north/east are expected with the convergence activity, before
returning back to the south by roughly 07-09Z. Couple higher gusts
to 20 kt cannot be ruled out. Expect ceilings to briefly return to
MVFR Monday morning.

HPR

&&

.MARINE...Breezy winds continue to diminish in the coastal waters
and Strait of Juan de Fuca areas this morning behind a cold front
that went through yesterday. Another weak trough will pass through
the waters Sunday afternoon into Monday. As high pressure builds
offshore, a descent push of onshore flow is expected late Sunday
into Monday with northwesterlies pushing through the Strait of Juan
de Fuca, and the northwestern portions of the coastal waters. Winds
will peak in these areas of up to 20 to 25 kt, and a couple spots
may see gusts approach 30 kt. Post-trough, there are no wind/weather
concerns at this time for the remainder of the week.

Seas in the coastal waters will steepen to 8-10 feet at roughly 10
seconds (the steepest seas will be in the northern half of the
coastal zones today with 9 second periods). Expect a drop down to 5
to 7 feet Monday through the rest of the week.

HPR

&&

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

&&

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

     Small Craft Advisory from 11 AM this morning to 2 AM PDT Monday
     for Central U.S. Waters Strait Of Juan De Fuca-Coastal
     Waters From Cape Flattery To James Island Out 10 Nm-East
     Entrance U.S. Waters Strait Of Juan De Fuca-West Entrance
     U.S. Waters Strait Of Juan De Fuca.

     Small Craft Advisory until 5 AM PDT early this morning for
     Coastal Waters From Cape Flattery To James Island 10 To 60
     Nm-Coastal Waters From Cape Flattery To James Island Out 10
     Nm-Coastal Waters From James Island To Point Grenville 10
     To 60 Nm-Coastal Waters From James Island To Point
     Grenville Out 10 Nm-Coastal Waters From Point Grenville To
     Cape Shoalwater 10 To 60 Nm-Coastal Waters From Point
     Grenville To Cape Shoalwater Out 10 Nm.

     Small Craft Advisory from 2 PM this afternoon to 11 AM PDT
     Monday for Coastal Waters From Cape Flattery To James
     Island 10 To 60 Nm-Coastal Waters From James Island To
     Point Grenville 10 To 60 Nm.

&&

$$