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000
FXUS66 KSEW 202221
AFDSEW

Area Forecast Discussion
National Weather Service Seattle WA
321 PM PDT Sat Apr 20 2024

.SYNOPSIS...A cold front will continue to progress eastward across
the region tonight with continued shower activity through Sunday
afternoon. High pressure will allow conditions to dry out and warm
up to start off next week with a chance of wetter and cooler
conditions returning by Wednesday.

&&

.SHORT TERM /TONIGHT THROUGH TUESDAY/...The Seattle metro area
reached temperatures in the low to mid 70s earlier this afternoon
ahead of an advancing cold front. As of 3 PM MDT, winds ahead of
the cold front have picked up across the region with many
observation sites reporting wind gusts between 30-40 mph. A
trained spotter reported a temperature drop of 11 degrees in half
an hour in southern Pierce County, with a rapid drop in
temperatures on tap for the rest of the region tonight as the cold
front continues to push eastward. Most areas will see a 10 to 15
degree difference in high temperatures between today and tomorrow
as much cooler air settles in.

A band of precipitation will continue to progress inland
throughout this evening along with the front, though westerly flow
aloft will cause some rain shadowing east of the Olympic
Mountains. The lowlands will generally see a tenth of an inch of
rainfall or less with this push. Snow levels will bottom out near
2500 ft, with an inch or two of snow accumulation still on track
through the Cascade passes. The highest snowfall totals will be
confined to the North Cascades with totals nearing a foot above
6000 feet in these areas. Breezy winds will wind down behind the
cold front with shower activity continuing through Sunday
afternoon. Mesoscale forecast models continue to suggest
convergence shower activity forming over Snohomish and King
Counties on Sunday, though confidence remains low on exactly where
and how intensely any convergence showers would form. Confidence
is higher for additional light accumulations Sunday afternoon and
evening through Stevens Pass, but accumulations will have little
impact to travel through the Cascades.

Frost is likely to form overnight into Monday morning for much of
the region as skies clear and winds ease. High pressure will build
inland on Monday and Tuesday, allowing conditions to dry out and
temperatures to rebound. Highs will return to the upper 60s by
Tuesday, with the potential for some areas to reach 70 degrees.

.LONG TERM /WEDNESDAY THROUGH SATURDAY/...Ensembles continue to
show a wide variety of solutions in the extended period, but are
favoring a progressive weather pattern for Wednesday and beyond.
Temperatures will hover near or slightly below normal with a
chance of light precipitation across western Washington each day.

Lindeman

&&

.AVIATION...Flow aloft has switched to the southwest as a cold front
is working its way onshore this afternoon. Surface winds have picked
up out ahead of the front out of the south-southwest, with gusts
observed up to 28 kt at KOLM this afternoon (37 kt at KHQM). Based
on these trends, will up winds for remaining terminals out ahead of
the front to 25-30 kt as the system continues to advance to the
east. The windiest periods will be Saturday afternoon/evening,
before winds die down late tonight. Post front, the winds will flip
to the west early Sunday morning, and then flip to the north late
Sunday afternoon. Winds remain around 8 to 10 kt overnight, but
occasional gusts to 20 kt are still possible for the remainder of
the TAF period.

A line of rain showers are also coming onshore ahead of the front.
They remain light, but expect ceilings to drop to low-end VFR
(possible MVFR along the coast briefly this afternoon and evening).
While the main line of rain will go through this evening, residual
showers (including post-frontal convergence zone over Snohomish
County) cannot be ruled out. Coverage is expected to be isolated on
Sunday, with partial clearing of the ceilings Sunday afternoon.

KSEA...High clouds filling in this afternoon ahead of a cold
front/line of showers to the west. Arrival time for the rain
expected after 00Z, then residual showers are possible overnight
through Sunday afternoon (convergence zone possible to the north in
Shohomish county). CIGs at this time do not drop below VFR (but will
hover around 4,000 ft with the rain). Winds picking up this
afternoon out of the southwest (gusts to 25-30 kt possible), with a
further shift to the west Sunday morning, and to the north Sunday
afternoon (decreased to 10 kt with gusts to 20 kt possible).

HPR

&&

.MARINE...An upper level ridge is giving way to a shortwave trough
this afternoon, with a surface cold front moving inland this
afternoon with rain showers. Winds have picked up across all waters,
and have expanded the small craft advisory to include the Northern
Inland Waters, and the Admiralty Inlet through tonight (based on
observations to the west and upper-end model guidance). Have also
upgraded the Central/East Strait of Juan de Fuca to Gale Warnings
with a higher chance of 35 kt winds. Otherwise, winds of 25 to 30 kt
will be possible out of the southwest ahead of the front for
remaining areas.

Once the main line of showers push through, winds will turn to the
west and diminish Sunday morning. An additional push down the Strait
of Juan de Fuca will occur Sunday afternoon with winds up to 25 kt.
Winds turn northerly Sunday evening into Monday. Winds up to 20 kt
are possible in Puget Sound waters Monday. Otherwise high pressure
will remain over the waters for the first part of next week,
resulting in onshore flow and pushes down the Strait.

Seas this afternoon are at 5 to 7 feet, but will rise to 8 to 12
feet this evening through Sunday morning before decreasing to 6 to 8
feet by Sunday evening.

HPR

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...None.
PZ...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-West Entrance U.S. Waters Strait Of
     Juan De Fuca.

     Gale Warning until 5 AM PDT Sunday for Central U.S. Waters
     Strait Of Juan De Fuca.

     Gale Warning until 11 PM PDT this evening for East Entrance U.S.
     Waters Strait Of Juan De Fuca.

     Small Craft Advisory until 11 PM PDT this evening for Northern
     Inland Waters Including The San Juan Islands-Puget Sound
     and Hood Canal.

     Small Craft Advisory until 8 PM PDT this evening for Admiralty
     Inlet.

&&

$$