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362
FXUS66 KSEW 172223
AFDSEW

Area Forecast Discussion
National Weather Service Seattle WA
323 PM PDT Tue Sep 17 2024

.SYNOPSIS...
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Clouds and rain chances increase across the region
tonight ahead of an approaching frontal system. Lingering rain
showers into Wednesday, especially in a potential Puget Sound
Convergence Zone, as the upper trough pushes eastward. A break in
the rain and clouds for Thursday, but this will be brief as
additional rounds of unsettled conditions will continue through
the weekend and into early next week.
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.SHORT TERM /TONIGHT THROUGH FRIDAY/...
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A rather cool and cloudy
afternoon is underway across Western Washington, as temperatures
hover around 60 degrees. NWS radar depicts increasing rain
offshore and extending eastward into the Olympic Peninsula
already. This will continue to advance eastward through the night,
with the highest rainfall accumulations (around half an inch)
expected west of Puget Sound and in the Cascades. The bulk of the
actions pushes through the region overnight, but as the upper
trough pushes south and east, expect strengthening onshore flow to
bring some light drizzle or rain through the morning. Meanwhile,
some lingering showers are likely to develop in a Puget Sound
Convergence Zone early Wednesday. Expect a lull in the clouds and
rain showers late Wednesday through Thursday with weak high
pressure somewhat building over the region. The next disturbance
is likely to arrive (or at least approach) by Friday, bringing
another increase in cloud cover and cooler temperatures.

.LONG TERM /SATURDAY THROUGH TUESDAY/...The weekend will continue
with a decidedly fall-like pattern as zonal flow aloft sets up
and keeps the door open for a series of disturbances through the
first half of next week. This will maintain abundant cloud cover
and rain at times, while temperatures hold below seasonal normals.
Will need to monitor the evolution of these features as subtle
shifts in the storms can yield significant shifts in where the
moisture sets up and the resulting impacts in clouds and
temperatures. This is reflected in the probabilistic NBM guidance
exhibiting some quite large spreads in values as we get into the
early part of next week. 12
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&&

.AVIATION...
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West to southwest flow aloft will become
light east/northeasterly tonight. At low levels onshore/southerly
flow will ease overnight with widespread light and variable winds
lingering into Wednesday morning. Widespread MVFR ceilings across
the interior lowlands this afternoon may continue to lift this
afternoon and evening with periods of VFR conditions - prevailing
conditions will likely linger in the 2500 to 3000 foot range. For
the coast conditions will remain 800 to 1200 feet. Areas of light
rain along the coast will linger into the evening.

KSEA...VFR ceilings 3000 to 3500 will linger into the evening then
lower overnight dipping to 1000 to 1500 feet between 10 and 14z with
a 70% chance of ceilings below 1000 feet by 14Z. Southwesterly
surface winds 5 to 7 knots will ease and become light and variable
after 06Z.
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&&

.MARINE...
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A weak surface low passing to the southwest this afternoon
and evening will result in gusty easterly winds over the coastal
waters into this evening before easing overnight. Offshore surface
high pressure returns Thursday into Friday helping boost
northwesterlies and possible small craft advisory levels with
combined seas rising to 7-9 feet late in the week, particularly
across the outer coastal waters.
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&&

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

&&

$$