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-- Discussion containing changed information from previous version are highlighted. --
000
FXUS66 KSEW 291619
AFDSEW

Area Forecast Discussion
National Weather Service Seattle WA
919 AM PDT Wed Mar 29 2023

.SYNOPSIS...
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High clouds spinning around an upper level low well
south of the area will move over the southern portion of Western
Washington today. Conditions get cooler and wetter again from
Thursday onward as a weak upper level trough moves into the
region. A seasonally strong frontal system will cross the area
Friday night into Saturday, with showers expected in its wake over
the weekend. Upper level troughing will then persist over the
Pacific Northwest into early next week, with another system slated
to arrive Tuesday.
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&&

.SHORT TERM /TODAY THROUGH FRIDAY/...
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Satellite imagery shows upper
level low moving south towards San Francisco this morning.
Southeasterly flow aloft around the low spreading high level
clouds over the southern portion of the area this morning. Doppler
radar indicating a few showers with the cloud cover but most of
this precipitation is not reaching the ground. Mostly clear skies
over the northern half of Western Washington. Temperatures at 9
am/16z were in the mid 30s to near 50.

Upper level low will continue to move southeast today pulling the
cloud cover south of Western Washington later this afternoon.
Winds in the passes overnight were easterly 15 to 25 mph but with
the cross cascade gradient now positive the winds in the passes
have eased. Even with the sunshine today for most of the area,
without any offshore flow highs will just be a couple degrees
above normal, in the mid 50s to lower 60s.

Flow aloft becoming northwesterly tonight. Weak trough embedded
in the flow moving over Western Washington later Thursday giving
the area a chance for showers Thursday evening into Friday
morning. Highs Thursday will cool back down into the lower to mid
50s.

A more substantial shift in the weather is then on tap Friday
into the weekend as a seasonally strong frontal system approaches
and brings with it widespread rain and heavy mountain snow to the
region. Front reaching the coast Friday night and moving inland
overnight into Saturday. Snow levels will fall to below pass
level, so can expect periods of snow to potentially yield travel
impacts across the Cascade passes. At this time, winter headlines
still appear likely with future forecast packages. High
temperatures will be in the upper 40s to low 50s.

Forecast in good shape this morning. No updates. Felton/14

.LONG TERM /SATURDAY THROUGH TUESDAY/...Previous discussion
follows. Showery and unsettled weather is expected to persist
across the region Saturday and Sunday in the wake of the
aforementioned frontal system. The upper level trough influence
will become greater over the weekend and conditions look to become
increasingly unstable in the cooler, post-frontal airmass. Thus,
can expect some shower activity to be convective - and cannot rule
out some lightning potential or small hail in any of the heavier
post-frontal showers. High temperatures over the weekend will
primarily range in the mid 40s to near 50, with lows expected to
be in the mid 30s to low 40s.

Guidance remains in good agreement with upper level troughing
remaining the dominant influence across the Pacific Northwest
headed into early next week. Another system then looks to drop
down along British Columbia and into our area on Tuesday, bringing
the potential for another round of lowland rain and mountain
snow. With a cool airmass in place and snow levels remaining low,
a rain/snow mix may still be possible for portions of the lowlands
during the early morning hours. High temperatures will be in the
upper 40s to low 50s, with overnight lows expected to be in the
low to mid 30s. 14
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&&

.AVIATION...
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Upper level low pressure near the CA Coast continues to
spread SCT-BKN mid level clouds around 10,000ft this morning. Cloud
cover may scatter some into the afternoon, with high clouds then
increasing from the north. Winds will shift from N/NE today (4-6kts)
to W/SW (still 4-6kts) this evening as the flow transitions to
onshore ahead of the next weak weather system. Onshore flow
overnight tonight will help usher in low clouds along the coast,
approaching OLM  around daybreak Thurs.

KSEA...VFR conditions today and tonight, with ceilings developing
and lowering Thursday morning to low-end VFR/high-end MVFR. N wind
expected to shift more SW around mid-evening this evening 4-6kts.

Kovacik
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&&

.MARINE...
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Weak high pressure influence through most of today will
yield mostly tranquil marine conditions with light winds and benign
seas. A weak storm system will move into the area later tonight and
Thursday, helping turn the wind field from north/northeasterly to
more onshore west/southwesterly. Expect cloud cover to increase with
the eventual development of a few showers tomorrow
afternoon/evening. Before this storm system arrives, expect a
westerly push of wind down the Strait as winds shift onshore this
evening, likely reaching SCA levels (Advisory is already in place).

A much stronger storm system/frontal system is still expected for
Friday and Saturday, bringing widespread rain and much breezier
conditions (some gale force winds could be possible, especially
around the East Entrance and Admiralty Inlet area). Active weather
looks to continue through the remainder of the weekend and early
next week.

Kovacik
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&&

.HYDROLOGY...
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No river flooding expected in the next 7 days.
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&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...None.
PZ...Small Craft Advisory from 6 PM this evening to 9 AM PDT Thursday
     for Central U.S. Waters Strait Of Juan De Fuca-East
     Entrance U.S. Waters Strait Of Juan De Fuca.

&&

$$