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Area forecast discussion 
National Weather Service Seattle Washington
915 PM PDT Friday Aug 22 2014...corrected unstable air mass associated with an upper low over
the interior of the Pacific northwest will generate a few showers
this evening over the Cascades. Otherwise higher pressure aloft is
forecast to nose into the region this weekend for more sunshine
after areas of morning clouds and warmer daytime temperatures. This
warming trend is expected to continue into the middle of next week.


Short term...latest radar/satellite imagery indicate rapidly
decreasing shower activity over the Cascades this evening. This is
probably the last of the precipitation for several days as the upper
low pressure circulation shifts eastward out of the area. Weaker onshore
flow will also result in less stratus making it into the interior
later tonight and Saturday morning. Most of the low clouds will
likely be confined to the coast...Strait...and near the lower
Chehalis gap given the light westerly gradient.

The Pacific northwest will remain between the long wave trough and offshore
ridging over the weekend. 500 mb heights rise just slightly through
Saturday but lack of onshore flow and sunshine will allow
temperatures to warm to near 80. An upper level short wave embedded
in northwest flow aloft will clip the area Sunday. Heights come down and
onshore flow could pick up a bit more than previous models were
showing. High temperatures will ease off back to the 70s if the
latest European model (ecmwf)/GFS runs are correct with the lower height trend. High
pressure builds stronger over the region Monday with high
temperatures trending back toward the low 80s. Mercer

Long changes from previous discussion...the upper ridge
axis begins to shift inland on Wednesday and heights falling a bit.
The forecasts start to diverge at this point with the GFS the most
aggressive in bringing a trough offshore Friday spreading precipitation
onshore. The Canadian and European model (ecmwf) also sag heights offshore but hold
precipitation at Bay. So for now...will cool daytime temperatures a bit
Wednesday through Friday with some increase in cloud cover by
Friday. Will also introduce a small threat of showers Friday and
would not be surprised we adjust to hold off any precipitation until - of
course - the Holiday weekend. Buehner


Aviation...upper level low near Oregon/Idaho border will continue
to move east overnight into Saturday morning. Northerly flow aloft
becoming northwesterly on Saturday.

Weak onshore flow pattern will continue through Saturday. Satellite
imagery shows stratus right along the coast with little movement
inland at 04z. With the light onshore flow stratus will not make it
much further east then the southern portion of Hood Canal to the
south Saturday morning. Stratus moving down the Strait overnight
could get as far east as kpae Saturday morning. The layer will be
shallow so what little stratus does get inland will burn off
quickly. With the light gradients fog...ceilings 200 feet or less
and visibilities below a mile... also a possibility over the
southwest interior 14z-18z Saturday. Stratus confined just to the
coastline by 19z.

Ksea...mostly clear skies with light north to northeast winds
overnight into Saturday morning. Winds becoming northwest 6 to 10
knots Saturday afternoon. Felton


Marine...a large surface high over the NE Pacific combined with
lower pressure over eastern Washington will maintain an onshore flow pattern
across West Washington into early next week. Onshore flow will be typically
strongest during the late afternoon and evening hours and weakest
during the morning. Small Craft Advisory winds can be expected in
the central and east Strait each evening. An upper level trough
will move southeast across SW b.C. Saturday night and Sunday morning.
Surface pressure gradients along the coast will increase ahead of
the trough and should generate Small Craft Advisory winds over the outer coastal
waters Saturday evening. Kam/Felton


Sew watches/warnings/advisories...
Pz...Small Craft Advisory central and east Strait of Juan Delaware fuca




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