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fxus66 ksew 162215 

Area forecast discussion
National Weather Service Seattle Washington
300 PM PDT Wed Aug 16 2017 upper level ridge moving over the Pacific northwest
coupled with low level onshore flow will maintain seasonable Summer
weather with areas of morning clouds into Friday. A weak upper level
trough is expected to bring some cooling and possibly some drizzle
late Friday into Saturday morning. Another upper level ridge will
rebuild over the region Sunday through Tuesday for a bit warmer


Short term...westerly flow aloft across the Gulf of Alaska with
embedded weak shortwaves will continue through the rest of this
week. One shortwave that moved into British Columbia this morning
brought some middle and high clouds into western Washington during
the day today along with a few sprinkles. Those clouds should
continue inland tonight. Yet this system will also induce stronger
low level onshore flow and expect marine cloudiness along and off
the coast to spread inland overnight. Prog cross-sections show the
tops to be near 850 mb/5000 ft by Thursday morning and thick enough
to perhaps squeeze out a little drizzle.

The next positive tilt shortwave was crossing around 160w early this
afternoon. Progs concur that this shortwave will build some ridging
aloft ahead of it moving over the Pacific northwest Thursday. So anticipate
the marine cloud deck to thin out during the afternoon as a result.

The following shortwave is forecast to track into British Columbia on Friday with
heights aloft over western Washington sagging into Saturday. Will
retain a small threat of showers closer to the Canadian border and
in the mountains with some orographic flow later Friday into
Saturday morning. Renewed stronger low level onshore flow should
result in a blanket of marine clouds across much of western
Washington Saturday morning. Anticipate daytime temperatures to be a
bit cooler - close to or just under average Saturday. Buehner

Long term...what's left of former typhoon banyon was located near
37n/160e and becoming extratropical. The mid-range progs continue to
build ridging downstream from this system over the Pacific northwest Sunday
into Monday for a return to less morning marine clouds and more warm
sunshine early next week. The Seattle-North Bend or surface pressure
gradient turns offshore by Monday morning. Again, there are 5 days
to go before the eclipse...but at this point any morning marine
clouds may be limited to just the coastal region and any inland
should be short-lived.

Heading into the Tuesday and Wednesday, the mid-range guidance
offers a developing upper level trough off the coast with a growing
threat of showers. The Euro is faster and stronger while the GFS and
Canadian are slower and weaker with this trend. For now have
introduced a threat of showers and some cooler temperatures on
Wednesday. Buehner


Aviation...northwest flow aloft will continue. A weak disturbance
embedded in the flow will bring patchy drizzle to the coast Thursday
morning. Low level onshore will also persist. Expect MVFR cigs over
the coast to advect inland across the lower elevations overnight.
Areas of IFR cigs/MVFR cigs will dvlp over the coast after 0900 UTC.

Ksea...MVFR cigs are expected after 0800 UTC (1 am thursday). VFR
conditions should return by 2000 UTC (1 PM thursday). Westerly flow
will become northerly this evening before becoming light and
variable late tonight. Winds will become westerly 5-10 kt Thursday


onshore flow of varying strength will continue through early next
week due to persistent high pressure offshore with lower pressure
east of the Cascades. The onshore flow will be strong enough for
gale force westerlies over the central and eastern Strait of Juan de
Fuca late today and tonight. There is a possibility of gale force
winds over the same area Friday evening.


Sew watches/warnings/advisories...
Pz...Gale Warning until 2 am PDT Thursday for central U.S. Waters
Strait of Juan de Fuca-East Entrance U.S. Waters Strait of
Juan de Fuca.

Small craft advisories are in effect for the Admiralty Inlet,
northern inland waters, and the West Entrance to the Strait of
Juan de Fuca.



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