Area Forecast Discussion
Issued by NWS Seattle/Tacoma, WA

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FXUS66 KSEW 230429
AFDSEW

Area Forecast Discussion
National Weather Service Seattle WA
929 PM PDT Thu Jun 22 2017

.SYNOPSIS...An upper ridge will bring dry weather with a warming
trend through the weekend. The ridge will shift inland early next
week with onshore flow developing for a return to more seasonable
temperatures and some night and morning clouds.

&&

.SHORT TERM...An upper ridge will build over the area through
Saturday. At the same time, low level onshore flow will be
northerly or even slightly offshore as a thermal trough pushes
north up the coast. This will result in sunny weather Friday and
Saturday with a warming trend. Highs will be in 70s to lower 80s
Friday and in the 80s to near 90 on Saturday.

The upper ridge axis will shift over Eastern Washington on Sunday
and weak onshore flow will begin to develop later in the day as a
thermal trough over the coast shifts inland. It will be another
very warm day for the interior - likely the warmest of the season
so far - with highs in the mid 80s to mid 90s. The coast should
start to see some cooling as onshore breezes kick in during the
afternoon although the amount of cooling is a bit uncertain for
now. Schneider

.LONG TERM...Previous discussion...The long-wave upper ridge axis
shifts east of the area Sunday night and Monday. Many models are
rather robust in shifting pressure gradients onshore as the ridge
moves eastward Sunday evening, resulting in significant cooling on
Monday. However, there is the hint of a short wave ridge offshore
at the mid levels that would only result in a partial marine push
Sunday night, with a more significant one Monday evening. Our
current forecast reflects the latter scenario and results in
cooling for Monday, but still warm in the Puget Sound area and
near the Cascades.

After a stronger marine push on Monday, a weak trough of low
pressure aloft combined with moderate onshore flow will result in
night and morning clouds and temperatures near to slightly below
average Tuesday onward. Albrecht

&&

.AVIATION...A strong upper ridge axis will slowly move from its
current position near 135W to east of 130W on Friday evening.
Moderate northwest flow aloft will weaken a bit on Friday. The air
mass will be dry and stable, with clear skies prevailing.

KSEA...Clear skies and north flow for the next 30 hours. Haner

&&

.MARINE...A northeast-southwest oriented surface ridge will
remain over the Pacific through Saturday. Meanwhile, a strong heat
low over California and southern Oregon will set up northerly
gradients over the waters. Winds over the coastal waters are
following a diurnal cycle, with northerlies peaking during the
late afternoon and evening, then falling off during the morning.
This cycle will repeat itself on Friday and Saturday. Gradients
will weaken on Sunday, then onshore flow will quickly increase on
Sunday night. Haner

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...None.
PZ...Small Craft Advisory until 3 AM PDT Friday for Coastal Waters
     From Cape Flattery To James Island 10 To 60 Nm-Coastal
     Waters From Cape Flattery To James Island Out 10 Nm-Coastal
     Waters From James Island To Point Grenville 10 To 60 Nm-
     Coastal Waters From James Island To Point Grenville Out 10
     Nm-Coastal Waters From Point Grenville To Cape Shoalwater
     10 To 60 Nm-Coastal Waters From Point Grenville To Cape
     Shoalwater Out 10 Nm.

&&

$$

www.weather.gov/seattle

You can see an illustrated version of this discussion at
www.wrh.noaa.gov/sew/gafd/latest_webafd.html



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