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578
FXUS66 KSEW 231529
AFDSEW

Area Forecast Discussion
National Weather Service Seattle WA
829 AM PDT Sun Jun 23 2024

.SYNOPSIS...An upper level trough will produce clouds, cooler
temperatures, and a few showers across Western Washington today.
The trough will weaken tonight and a ridge of high pressure aloft
will begin to rebuild into the area Monday. The ridge will
strengthen as it shifts eastward on Tuesday for dry conditions and
warmer temperatures. Another trough arrives Wednesday into
Thursday for showers and cooler temperatures once again. A weak
ridge late in the week will lead to drier conditions and near
normal temperatures.

&&

.UPDATE...
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No major changes to the forecast. Expect off an on light
showers to continue throughout the day today, with a noticeable
cool-off in high temperatures today in the low to mid 60s. Please
see the discussion below for more details (as well as a refreshed
aviation).

HPR
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&&

.SHORT TERM /TODAY THROUGH TUESDAY/...
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Clouds have filled in
across most of Western Washington early this morning ahead of an
upper trough moving into British Columbia. Spotty showers have
already been observed across coastal areas and we should see some
weak convergence zone activity develop across Skagit and Snohomish
counties later this morning. QPF will be minimal...a few
hundredths at best. High temperatures will be back below
normal...in the 60s across most of the lowlands.

The upper trough weakens tonight into Monday as it shifts
eastward across interior British Columbia and this will allow
upper ridging to begin rebuilding into the area. Most areas should
see some sunshine return Monday afternoon with temperatures
rebounding to near seasonal norms. Upper ridging gains amplitude
as it shifts eastward into the northern Rockies later Tuesday.
Interior temperatures will warm into the 70s while onshore flow
keeps most of the coast firmly in the 60s.

.LONG TERM /WEDNESDAY THROUGH SATURDAY/...Models remain
consistent with an upper trough moving into the region Wednesday
and Thursday. This one has a more southward trajectory than the
current one and looks to provide much of the region with a decent
chance at some measurable precip. And as one would expect,
temperatures will cool back to below normal levels midweek. The
upper trough shifts eastward into the Northern Rockies by the end
of week allowing weak upper ridging to briefly rebuild. With
continued onshore flow, temperatures will be held around seasonal
levels...60s coast...70s inland. 27
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&&

.AVIATION...
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Upper level trough over Western Washington today
moving east tonight. Zonal flow aloft tonight and Monday. Onshore
flow will persist in the lower levels through Monday.

Satellite imagery shows clouds have made it all the way to the
Cascade crest this morning, with ceilings at area terminals mainly
a mix between VFR and MVFR. Light showers will possible today,
with greatest chances of shower activity expected for terminals
along the coast and KPAE northward. Expect ceilings to become more
widespread VFR between 20Z-23Z. High-res guidance does indicate a
weak convergence zone developing over northern King and Snohomish
counties this afternoon and evening, which could bring localized
MVFR ceilings in showers to KPAE at times. VFR ceilings look to
continue for the majority of area terminals into Monday morning,
with the exceptions being KHQM along the coast, where lower
ceilings look to move back in tonight, and KPAE in any lingering
convergence showers.

KSEA...VFR ceilings, though could still see some brief periods of
MVFR through the morning hours today. Expect ceilings to be mostly
VFR this afternoon and evening. High-res guidance indicating PSCZ
will stay to the north of the terminal. Southwest wind 10 to 14
knots, with gusts to 20 kt possible at times through the day.
Winds will ease back to 4-8 kt after 03Z. 14
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&&

.MARINE...Weak high pressure will build back over the
coastal waters and interact with lower pressure inland today
through Tuesday. Another frontal system will reach the waters
Wednesday. High pressure will rebuild over the coastal waters
Thursday.

Diurnal westerly pushes through the Strait of Juan de Fuca could
result in small craft advisories for the Central and Eastern
Strait Tuesday through Thursday in the evenings.

Swell near 4 feet this morning building to 5 to 7 feet tonight
into Monday. Felton

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
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WA...None.
PZ...None.
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&&

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