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700
FXUS66 KSEW 092143
AFDSEW

Area Forecast Discussion
National Weather Service Seattle WA
243 PM PDT Mon Sep 9 2024

.SYNOPSIS...
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A series of systems will move across the region this
week, bringing increased onshore flow, below normal temperatures,
and shower chances to western Washington at times.
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&&

.SHORT TERM /TONIGHT THROUGH THURSDAY/...
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Zonal flow aloft and
increased onshore flow in the low levels allowed for marine
stratus to push inland into the interior this morning. Satellite
imagery this afternoon shows stratus still draped across much of
the interior and shows clouds scattering out very slowly. Stratus
will continue to lift and gradually scatter through the remainder
of the afternoon, but can expect some areas to stay cloudy through
the rest of the day. Afternoon high temperatures will top out in
the 60s and 70s across the region.

A trough will then sink south from the Gulf of Alaska and deepen
offshore on Tuesday. Onshore flow will continue across western
Washington, allowing for another marine push to usher in another
round of stratus on Tuesday morning. Mid to high level clouds will
increase throughout the day ahead of this next system and
afternoon highs are expected to top out in the upper 60s to low
70s. Showers look to start spreading inland along the coast by
Tuesday evening.

The upper level low will then move inland across the region on
Wednesday, sweeping a frontal system across western Washington.
Temperatures will cool even more, with afternoon highs expected to
to be in the 60s area-wide. This system will bring the next best
chance of wetting rains to the region, mainly along the coast,
central and south Sound, and central Cascades. Rainfall amounts
generally look to be around a quarter of an inch for most lowland
locations, though may trend closer to half an inch for areas along
the coast and in the mountains. Higher elevations of Mount Rainier
will even see a few inches of snow accumulations as more fall-
like conditions return.

A brief break in the unsettled conditions will be possible on
Thursday as the upper level low moves off to the east and a
shortwave ridge nudges into the region. Showers may linger across
the mountains, but will generally remain light. Afternoon high
temperatures will remain cool and are expected be in the 60s to
low 70s.

.LONG TERM /FRIDAY THROUGH MONDAY/...Ensemble guidance is in decent
agreement of another trough moving into the Pacific Northwest
over the weekend, however there remains some uncertainty in
regards to its amplitude. Regardless, this will continue to
promote below normal temperatures and chances of showers across
western Washington through much of the long term. 14
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&&

.AVIATION...
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Southwesterly flow aloft as a weak trough moves over
western Washington.

Stratus remains in place across the Puget Sound through stilt
and cameras are hinting at it slowly breaking up and evaporating
from northwest to southeast. Ceilings remain MVFR through most area
terminals. The slow breakup of the stratus may allow for ceilings to
scatter to VFR around 22-23Z. Scattered ceilings will remain tonight
before filling back in between 09-12Z and dropping to IFR through
the early morning hours, before again rising and breaking up to VFR.
Mid and high level cloud cover will increase tomorrow ahead of an
incoming frontal system that will approach the area tonight.

Southwesterly winds will turn northwesterly this evening and lighten
up. Light winds will turn back to southwesterly early this morning
and strengthen to 4 to 8 kt tomorrow.

KSEA...MVFR cigs continue as stratus slowly breaks up over the
terminal.  Winds southwesterly switch back to the northwest around
01-02Z this evening at 5 to 7 kts, becoming light this evening.
Winds will switch back to southwesterly tomorrow morning and
increase to around 4 to 8 kt tomorrow.

LH
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&&

.MARINE...
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Winds will continue to be northwesterly across the coastal
waters tonight. Winds will switch to southwesterly late Tuesday
night ahead of an incoming frontal system that will move through the
area waters early Wednesday morning. There is a chance for some
Small Craft Advisory winds Tuesday evening (30-60%) in the Central
Strait of Juan de Fuca as the system begins to approach the area.
Winds switch back to northwesterly Wednesday and remain like so
through the end of the week.

Seas 4 to 6 ft will continue through tomorrow before rising to 6 to
8 ft behind the frontal system Wednesday into Thursday before
subsiding back to around 4 to 5 ft through the end of the week.

LH
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&&

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

$$