Area Forecast Discussion
Issued by NWS Seattle/Tacoma, WA

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FXUS66 KSEW 182137

Area Forecast Discussion
National Weather Service Seattle WA
237 PM PDT Thu May 18 2017

.SYNOPSIS...Weak high pressure will be over the area through Friday.
A weak upper trough will reach the area Friday night and Saturday. A
stronger upper ridge will build for sunny warm weather for the first
part of next week.


.SHORT TERM...Clouds will give way to more sunshine by Friday
afternoon and temps will warm a notch Friday. A weak upper trough
will reach the area Friday night so there will be an increase
in onshore flow and a chance of a few showers over Western
Washington Friday night and Saturday. So, a little warmer and
sunnier Friday, cooler and cloudier with a chance of showers Friday
night and Saturday then warming up as an upper ridge begins
to build on Sunday.

.LONG TERM...Sunny and much warmer weather is in the extended
forecast as the center of an upper ridge drifts over the region
Monday and Tuesday. Highs should range from the 70s coast to the
lower 80s inland Monday and Tuesday before falling off midweek. The
12z GFS and ECMWF have different ideas about the latter part of the
week--The Euro has a cold upper trough moving through B.C. and
Alberta midweek with a rapid cool down for Western Washington while
the 12z GFS has a much weaker trough farther north and keeps weak
ridging over our area til late in the week.


.AVIATION...An upper level ridge will maintain a dry and stable
air mass across Western WA tonight. The flow aloft is
northwesterly. VFR conditions expected. Dry weather will continue
into Friday with the ridge in place. A weak upper level
trough may trigger isolated showers Friday night. 33

KSEA...VFR conditions tonight. Light/variable winds flipping to
N by 03z this evening. 33


.MARINE...A weak surface trough will cross the Coastal Waters
tonight. High pressure over the NE Pacific will maintain onshore
flow through the weekend. Highest wind and waves will be found
through the central/east Strait of Juan de Fuca. 33




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