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000
FXUS66 KSEW 210339
AFDSEW

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

.UPDATE...The cold front has moved east of the area late this
evening with post-frontal shower activity, as well as steadier
precipitation across the North Cascades. A convergence zone will
develop and continue into tonight for portions of Snohomish and
Skagit Counties. Otherwise, the best potential for showers into
Sunday morning will be along the Olympic Peninsula. Temperatures
will be cooler tonight in the upper 30s to mid 40s for the area.

&&

.SYNOPSIS...Post-frontal shower activity will continue 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 WEDNESDAY/...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 /THURSDAY THROUGH SUNDAY/...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...A frontal boundary is now east of the Cascades this
evening with post-frontal low level onshore flow gradually
weakening. Southwest flow aloft will become westerly overnight
through much of Sunday. Scattered showers will continue across the
area into Sunday with ceilings generally remaining at or above 3500
to 4500 feet. A weak convergence zone is expected to form over Puget
Sound early Sunday afternoon.

KSEA...A few post-frontal showers will remain in the vicinity of the
terminal, but they`ll be isolated. Ceilings will generally remain
at or above 3500 to 4500 feet into midday Sunday. A weak convergence
zone is possible between 20Z Sunday and 00Z Monday. Gusty SW surface
winds will gradually relax overnight becoming S/SW 7 to 10 knots by
early Sunday A.M. Winds will veer to N/NW near or after 00Z Monday.

27

&&

.MARINE...Small craft advisories will continue across most of the
waters overnight as post-frontal onshore flow gradually relaxes.
Surface ridging builds into the coastal waters on Sunday and this
will likely keep small craft advisory westerlies going in the
central/east strait into Sunday evening. The surface ridge shifts
inland on Monday as thermally induced low pressure expands
northward along the Oregon coast. This will turn the flow more
northerly...perhaps near advisory levels across southern portions of
the coastal waters. Another front is slated to reach the area
Tuesday night into Wednesday.

Seas may briefly get above 10 feet over portions of the outer
coastal waters tonight into Sunday before subsiding below that
threshold for the remainder of the forecast period. 27

&&

.HYDROLOGY...No river flooding is expected over the next 7 days.

&&

.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.

&&

$$