Area Forecast Discussion
Issued by NWS Seattle/Tacoma, WA

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204
FXUS66 KSEW 190234
AFDSEW

Area Forecast Discussion
National Weather Service Seattle WA
735 PM PDT Wed Apr 18 2018

.SYNOPSIS...An upper ridge will bring dry mild weather Thursday
into Friday. A frontal system will move quickly across the area
Friday night, followed by showers and sun breaks on Saturday. A
stronger upper ridge will bring another stretch of dry mild
weather Sunday through Wednesday.

&&

.SHORT TERM...Current radar is a reflection of the first weeks of
spring thus far...rain just keeps finding a way to hang on even
longer. To be fair...conditions are pretty quire over much of W
Wa...but showers still linger along the King/Snohomish county line
and another blob of showers over portions of Thurston...Pierce and
Lewis counties.

Models continue to show that this activity is expected to fizzle out
by midnight tonight as ridging over the Pacific starts to exert its
influence over the area. This ridge will keep conditions dry for
Thursday and most of Friday with afternoon high temperatures still
expected to reach into the lower 60s. The next chance for rain comes
in with a fast moving front expected to hit the coast Friday night
and work its way eastward during the overnight hours and into
Saturday morning. The front moves through pretty quickly...but
moisture with the associated upper level trough...remaining mostly
north of the border...will keep the prospect of showers in the
forecast into Saturday afternoon before tapering off Saturday night.

All in all...inherited forecast is in good shape and covers
lingering showers. No evening update needed.

.LONG TERM...From Previous Discussion...High pressure aloft will
produce a dry and mild spell Sunday through Wednesday. Highs will be
near normal Sunday but then warm several degrees into the 60s Monday
and remain in the 60s into the middle of the week. There is a little
uncertainty with the dry forecast by Tuesday when models show a weak
upper trough crossing the area but the consensus is dry for now. The
GFS shows a weather system reaching the area Wednesday with zonal
flow aloft but the ECMWF is dry with an upper ridge and is preferred
for now. Schneider

&&

.AVIATION...A weak upper level trough over the Pacific Northwest
will weaken tonight. An upper ridge offshore will strengthen and
move eastward into Western Washington later Thursday into Thursday
night. Light flow aloft this evening will become northwesterly
later tonight through Thursday as the offshore ridge strengthens
and approaches the region. At the surface, a ridge of high
pressure will strengthen over the offshore waters tonight and
Thursday.

Even though some showers linger over portions of W WA...conditions
expected to remain VFR this evening. As the air mass stabilizes
later this evening...mid-level clouds expected to dissipate leaving
only scattered cirrus or clear skies later tonight through Thursday.
Any fog or stratus early Thursday morning will be limited to favored
river valleys, mainly from about KSHN-KOLM southward. SMR/Albrecht

KSEA...VFR conditions will persist. Showers to the north and south
of the terminal not expected to move over the terminal...however may
allow for BKN mid-level clouds at times this evening until said
showers dissipate. After midnight...generally expected either SCT
high clouds or possibly even clear skies. North to northeasterly
winds 5-7 kt into Thursday morning before returning to NW 5-8 kt
by noon Thursday. SMR/Albrecht

&&

.MARINE...A ridge of high pressure will strengthen over the
offshore waters tonight and Thursday then move slowly eastward
into the interior of Western Washington on Friday. A combination
of the strengthening offshore ridge and differential heating
between the interior and coastal areas will result in the
development of Small Craft Advisory conditions over the eastern
two thirds of the Strait of Juan de Fuca Thursday afternoon into
Thursday night. Models have been persistent in these wind speeds and
as such...inherited headline looks good.

A moderate cold front will move through the waters Friday
evening. Small craft advisory south winds are expected to develop
over the coastal waters and at the entrances to the strait ahead
of the front. Strong westerly flow, possibly to gale strength,
will develop behind the front late Friday night across portions of
the Strait of Juan de Fuca. Will wait and see what 00Z model
solutions look like before determining the need for any additional
headlines.

Onshore flow will slowly weaken later Saturday through Monday.
SMR/Albrecht

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...None.
PZ...Small Craft Advisory from 5 PM Thursday to 2 AM PDT Friday for
     East Entrance U.S. Waters Strait Of Juan De Fuca.

     Small Craft Advisory from noon Thursday to 2 AM PDT Friday for
     Central U.S. Waters Strait Of Juan De Fuca.

&&

$$

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