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afdsew

Area forecast discussion
National Weather Service Seattle Washington
840 PM PDT Tue Aug 14 2018

Synopsis...an upper ridge will produce dry and warm weather
through Wednesday with smoke. Onshore flow will develop later
Wednesday and continue through Friday as a weak upper trough
approaches and eventually moves through. This will cool highs back
to near normal Thursday and Friday. High pressure aloft will
rebuild over the area on Saturday before another upper trough
moves into the region.

&&

Short term...an upper ridge will shift slowly inland tonight and
Wednesday. Wednesday will be another warm day for the interior but
smoke will continue to dampen highs a bit. The coast will be
cooler with some morning low clouds as onshore flow starts to
develop. Smoke and poor air quality will likely linger through
Wednesday. Smoke will probably start to clear near the coast later
in the day as onshore flow develops but most of the area likely
won't see much improvement until at least Wednesday night.

A weak upper trough will move over the area Wednesday night and
Thursday and inland on Friday. A marine push Wednesday night will
spread low clouds partially inland. This should help scour the
smoke plaguing the region. Low clouds Thursday morning will burn
off for a mostly sunny weather but the onshore flow will cool
highs back to near normal. Friday should be a typical Summer day
with morning clouds, afternoon sunshine, and highs near normal.
Schneider

Long term...previous discussion...upper level trough axis should
push east of the local area late Friday night into Saturday. Weak
ridging will take its place through the day on Saturday allowing
for a rather pleasant day and temps beginning to warm back up a
few degrees. The effects of the ridge will be short-lived however
as better consensus amongst the 12z operational GFS and European model (ecmwf) show
the development of a weak Rex block along the British Columbia and Washington
coastline by early Sunday. This would place the County Warning Area under better
influence of the trough portion of The Block, which may impact the
expected warming trend to some degree. Will opt to not get too
carried away and await later runs before determining impacts /if
any/ to the forecast. At this point in time it should be noted
that no precip is expected thru the extended. Trough should linger
thru the remainder of the extended. Kovacik

&&

Aviation...an upper ridge over the area will shift inland tonight
and Wednesday as an upper trough approaches from the west. Light
southerly flow aloft will increase and become southwest. At the
surface, a weak thermal trough over the interior of western
Washington will shift to the coast tonight. Onshore flow will
develop later Wednesday. The air mass is dry and stable.

Smoke will continue with widespread MVFR visibilities tonight and
probably for most of Wednesday. Visibilities should improve from
the west late in the day as onshore flow develops. Low clouds and
fog should develop at the coast tonight but they will remain
confined to near the coast until Thursday night when a marine push
will bring them inland.

Ksea...clear skies. There will be ceilings of 3000-4000 feet at
times in smoke however. Visibilities 2-4sm in smoke should also
be prevalent through tonight and probably most of Wednesday.
Northerly wind 5-10 knots will ease and become light tonight. West
to northwest wind 4-8 knots Wednesday afternoon. Schneider

&&

Marine...a weak thermal trough over the inland waters will shift
to the coast tonight. Onshore flow will develop later Wednesday
and continue through Friday. Small Craft Advisory strength west
winds are likely each night for the central and eastern Strait of
Juan de Fuca with a chance of gales Wednesday and Thursday
evening. There will also be Small Craft Advisory strength
northwest winds at times for the coastal waters Thursday and
Friday. Onshore flow will weaken on Saturday and perhaps turn
offshore on Sunday as a thermal trough develops along the coast.
Schneider

&&

Sew watches/warnings/advisories...
Washington...none.
Pz...none.

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