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Area Forecast Discussion (AFD)

Issued by Seattle/Tacoma, WA (SEW)

FXUS66 KSEW 170317

Area Forecast Discussion
National Weather Service Seattle WA
817 PM PDT Mon Jul 16 2018

.SYNOPSIS...Dry and warm conditions will linger over much of Western 
Washington into Tuesday. A weak upper level trough will brush the 
area Tuesday afternoon helping boost low level onshore flow setting 
up a return to normal high temperatures for Wednesday. A typical 
onshore flow pattern will follow through the weekend with night and 
morning clouds and normal high temperatures. 


.SHORT TERM...Another warm day across much of Western WA today
with temps in the interior reaching the 90s. Records were out of
reach for the day. The coast was the cool spot again due to
onshore flow. Highs along the coast were in the 60s to lower 70s.
Low level stratus clouds will form along the coast overnight and
possibly the Strait of Juan de Fuca too. Skies will remain mostly
clear in the interior. The current forecast is on track. 33

Previous discussion...Expect onshore flow to remain limited again
tonight, setting up Tuesday to be a transition day with normal 
temperatures along the coast and strait, and slightly cooler - but
still above normal temperatures for much of the interior. A dry, 
weak upper level trough will brush the area Tuesday afternoon 
boosting onshore flow Tuesday night into Wednesday morning. The 
more mature onshore flow, coupled with the zonal flow aloft will 
help a shallow marine layer penetrate further into the interior 
early Wednesday morning resulting in morning low clouds west and 
south of Puget Sound and a return to near normal high temperatures.
Highs over the interior will remain in the mid to upper 70, and 
the 60s along the coast and strait. 

.LONG TERM...Previous discussion...Medium range models continue 
to agree on a fairly typical zonal/onshore flow pattern persisting
through Thursday. This will mean night and morning clouds for at 
least parts of the interior and near normal temperatures. Models 
continue to advertise another upper level trough sliding down the 
British Columbia coast late Thursday into Friday morning before it
shifts inland Friday afternoon and evening. Models continue to 
show it shifting inland while still over British Columbia which 
will keep Western Washington dry. It's possible that there may be 
enough energy aloft to result in a chance of showers - mainly over
the north Cascades - but for now the forecast remains dry. The 
most likely impact will be some increased mid and high clouds as 
the upper level trough moves past the area to the north and an 
enhancement to the low level onshore flow Friday night. The bottom
line is that the typical pattern of night and morning clouds with
normal temperatures will keep through Friday and possibly 
Saturday. Upper level heights look to build Sunday coupled with a 
weaker onshore flow will result in a bit of warming especially by 


.AVIATION...The air mass across Western WA will remain dry and 
stable through Tuesday. The flow aloft is westerly. The coast will
see patchy low clouds or stratus during the morning for MVFR
conditions. Otherwise, VFR conditions expected in the interior. 

KSEA...N/NE wind 5-10 kt becoming S/SW 09-12z early Tue morning. 
VFR conditions expected. 33


.MARINE...High pressure over the NE Pacific will maintain
onshore flow across the region this week. Onshore flow will 
increase on Tuesday and Wednesday with gales possible through the
Strait of Juan de Fuca. 33


PZ...Gale Watch from Tuesday afternoon through late Tuesday night for 
     Central U.S. Waters Strait Of Juan De Fuca-East Entrance 
     U.S. Waters Strait Of Juan De Fuca.

     Small Craft Advisory until midnight PDT tonight for Central U.S. 
     Waters Strait Of Juan De Fuca.