Area Forecast Discussion
Issued by NWS Seattle/Tacoma, WA

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FXUS66 KSEW 171042
AFDSEW

Area Forecast Discussion
National Weather Service Seattle WA
340 AM PDT Thu Aug 17 2017

.SYNOPSIS...An upper level ridge moving over the Pacific Northwest
coupled with low level onshore flow will maintain seasonable summer
weather with areas of morning clouds today and 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
conditions.

&&

.SHORT TERM...Plenty of marine stratus over W WA this morning
and while a fair amount of it will burn off by late morning...might
see some patches of cloud linger over the Sound area...the SW
interior and along the coast into the late afternoon before skies
clear. Inherited some fog wording along the coast for this early
morning...and given the situation it certainly seems warranted...but
current temp/dewpoint gap might be suggesting this may not arise.
Will leave in forecast as there will be a few more hours of cooling
which may close said gap.

An upper level ridge will cross over the area today with continued
dry conditions expected. 500mb heights do not look to increase all
that much...and combined with lingering clouds...this should make
for little change in daytime high temps today. A decaying frontal
system will pass to the north of the area Friday and models still
suggest the southernmost part of said decaying front may just nick
the far NW tip of the Olympic peninsula...resulting in slight chance
pops there. Upper level troughiness lingers into Saturday but this
feature continues to have little impact on both temps and pops...as
conditions will remain seasonable and dry.  SMR

.LONG TERM...An upper level ridge building over the Pacific waters
will start to flex its muscles over W WA starting Sunday as 500mb
heights increase...signaling some warming. This ridge will pass
overhead Monday...with ECMWF increasing the amplitude of its
solution to match better with the GFS...so overall looks like
Eclipse day should see mostly clear skies. While the ridge axis
passes over the Cascades Tuesday...temps end up peaking Tuesday
afternoon before an upper level trough...and cooling
temperatures...enter the area for Wednesday.  SMR

&&

.AVIATION...Northwesterly flow aloft will become westerly this
morning. Low level onshore flow continuing into Friday. Stratus
along the coast and from just south of KPAE early this morning with
ceilings mostly in the 1000-2000 foot range with isolated ceilings
just below 1000 feet. Stratus will spread north to near KBLI by 15z.
Ceilings improving late in the morning. The clouds will scatter out
in the early afternoon hours with scattered clouds continuing
into the evening hours.

KSEA...Ceilings near 1000 feet through most of the morning hours.
Ceilings improving mid to late morning with the stratus scattering
out around 20z. Light southwesterly winds becoming northerly 4 to 8
knots this afternoon. Felton

&&

.MARINE...Onshore flow of varying strength will continue through
early next week due to persistent high pressure offshore with lower
pressure east of the Cascades. Small craft advisory winds are
expected in the central and eastern Strait of Juan de Fuca beginning
late in the afternoon and continuing into the early morning hours
each day through the weekend. For the remainder of the waters winds
are forecast to be 20 knots or less through the weekend with the
exception of the outer coastal waters on Saturday where winds will
rise to 25 knots. Felton

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...None.
PZ...Small craft advisory for Central U.S. Waters Strait Of
     Juan De Fuca the until 8 AM PDT today and from 5 pm this
     afternoon through early Friday morning.
     Small craft advisory for the East Entrance U.S. Waters
     Strait Of Juan De Fuca from 7 pm tonight until early
     Friday morning.

&&

$$

www.weather.gov/seattle

An illustrated version of this forecast discussion can be seen at
www.wrh.noaa.gov/sew/gafd/latest_webafd.html



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