449
FXUS66 KSEW 200353
AFDSEW

Area Forecast Discussion
National Weather Service Seattle WA
853 PM PDT Sat Apr 19 2025

.SYNOPSIS...Light isolated showers possible today. 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 /TONIGHT THROUGH TUESDAY/...Latest satellite imagery
shows mostly clear to partly cloudy skies across Western
Washington this afternoon. Radar activity remains pretty quiet as
well, besides some light isolated fleeting showers. Overall,
conditions look to remain generally dry this afternoon into most
of tonight. An upper level trough will move across the area on
Sunday bringing lowland rain and mountain snow. Lowland
accumulations will be light, around 0.05-0.25 inches, and snow
accumulations between 2.00-3.00 inches. Snow levels on Sunday will
be around 3500-4000 ft and will lower to around 2800-3000 ft late
Sunday night. Models are in general agreement for a convergence
zone developing Sunday afternoon/evening along Central Puget Sound
and the Central Cascades. In addition, some high-resolution
models hint at a band settling over Snoqualmie Pass. Depending on
where the band sets up, additional localized amounts are possible
along Snoqualmie Pass. HREF probabilities show there is a 40%
chance of exceeding 6 inches at Snoqualmie Pass. Convergence zone
activity will gradually weaken early Monday morning.

Conditions will begin to gradually dry out on Monday as the upper
level trough continues to push eastward and upper level ridging
builds offshore. A weak shortwave will move over the region on
Tuesday; however little to no precipitation is expected with this
system at this time.

.LONG TERM /WEDNESDAY THROUGH SATURDAY/...There is good agreement
among ensemble guidance that Western Washington will be under
upper level ridging on Wednesday and Thursday, bringing warmer
and dry conditions. Temperatures will peak on Thursday, with highs
reaching the upper 60s along the interior. Some locations along
the southern interior may approach 70 degrees. The ridge will
begin to push out of the region late Thursday night ahead of an
incoming trough. There is some disagreement among ensemble members
in terms of strength, timing, and trajectory with this trough.
However, there is good agreement among ensembles that cooler and
unsettled conditions are favored late in the week into the
weekend.

29

&&

.AVIATION...Northwesterly flow will persist aloft today as an
upper level trough gradually deepens over the region into Sunday.
VFR conditions prevail across the area this evening. More widespread
MVFR ceilings are expected headed into Sunday morning as the next
disturbance crosses the region. VFR conditions look to return behind
the frontal passage Sunday afternoon. As a result, shower activity
will increase across the region overnight into Sunday morning.
Breezy surface winds to 20-25 kt remain likely into this evening for
terminals along the Pacific Coast and along the Strait of Juan de
Fuca. Elsewhere, winds have been mostly west- southwesterly,
persisting at 5-10 kts this afternoon. The exception is KPAE, which
remains northerly at 5-10 kt. Expect winds to ease tonight and for
the interior terminals to see a more widespread shift back to the
southwest.

KSEA...VFR conditions prevail this evening. Winds remain out of the
south, persisting at 8 to 12 kt, before easing again later this
evening. Shower activity will increase in the vicinity of the
terminal overnight, with ceilings looking to drop to MVFR between 12-
15Z Sunday morning. VFR conditions look to return Sunday afternoon.
A PSCZ looks to develop late Sunday afternoon into evening, likely
sinking southward towards the terminal by Sunday night.

14/62

&&

.MARINE...Winds remain breezy across portions of the coastal waters
and the Strait of Juan de Fuca this evening but should begin to
start to ease going into early Sunday morning. The strongest winds
remain north and west of Admiralty Inlet, thus have cancelled the
advisory for tonight. Otherwise, the rest of the forecast remains on
track.

A weak disturbance will across the area waters Sunday afternoon into
Monday. Another onshore push is expected along the Strait Sunday
night into Monday, likely yielding another round of small craft
headlines. High pressure will then persist across the northeastern
Pacific through midweek, before weakening on Thursday as the next
system approaches the waters Thursday night into Friday.

Seas across the coastal waters remain steep and generally persist
around 8 to 9 ft at 9 seconds. Seas will slowly ease tonight,
becoming 6-8 ft on Sunday. A brief uptick towards 10 ft is possible
again late Sunday into Monday, before seas subside towards 4-6 ft on
Tuesday.

14/62

&&

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

&&

.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-West Entrance U.S. Waters Strait Of
     Juan De Fuca.

     Small Craft Advisory until 5 AM PDT Sunday 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.

&&

$$