Area Forecast Discussion
Issued by NWS Seattle/Tacoma, WA

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FXUS66 KSEW 201026
AFDSEW

Area Forecast Discussion
National Weather Service Seattle WA
330 AM PDT WED JUL 20 2016

.SYNOPSIS...An offshore upper low will move slowly toward Western
Washington through Thursday for partly sunny skies and a chance of
showers, mainly over the mountains during the afternoon and evening
hours. Thunderstorms are possible over the Cascades Thursday. A weak
upper ridge should bring sunnier weather Saturday through Tuesday.

&&

.SHORT TERM...Current IR satellite and obs show low clouds over many
portions of Western Washington this early morning...with the radar
echo free. Looking deeper into today...the upper level low still
over the coastal waters looks like it might eke out some showers
over higher elevations today...mainly limited to the Olympics and
the very North Cascades. However...the main driver in the expected
weather for today will be the heat dome that has been all the rage
in the Plains and Midwest lately. While temperatures may warm a
degree or two compared to yesterday...the main impact of the back
end of this ridge will be to keep conditions pretty dry for most
locations.

Getting into Thursday...the coastal low gets its act together and
pushes inland and the interplay between the two systems looks to
bring a return to showers and maybe even some thunderstorms to
eastern portions of the CWA Thursday afternoon and evening. At this
time...it does look like any thunder will be limited to the
Cascades...with showers possible elsewhere. Models have see-sawed a
bit on this in the past few runs...some models and runs being drier
at first...then flopping over to wetter. Current forecast reflects
an amalgamation that remains consistent with inherited forecast as
well as forecasts from surrounding offices. These showers may linger
into Thursday night and maybe even into very early Friday morning
before fizzling out. The thunderstorm threat for the Cascades will
be even more limited...not likely to make it out of Thursday evening
as conditions stabilize very quickly. By Friday afternoon...looks
like some minor ridging sneaks into the area...drying things out and
making for a nice start to the weekend.

.LONG TERM...The aforementioned minor ridge does look to amplify for
the remainder of the weekend...warming up temperatures in the
interior lowlands into the mid to upper 70s and answering the many
who have wondered where summer has been hiding this year. Once that
ridge moves on at the start of next week...an alternating pattern of
minor ridges and troughs will not make all that much impact in the
local weather...ultimately proving to be an extended dry period with
fluctuations in high temperatures generally ranging 2 to 5 degrees
and mainly staying within the 70s for interior lowland locations
into Tuesday of next week.  SMR

&&

.AVIATION...A broad upper low over the coastal waters will remain
stationary through tonight giving light southwest flow aloft. A weak
ridge of high pressure will remain over the coastal waters through
tonight. The air mass will be somewhat moist and mostly stable today.

VFR conditions prevail over most of Western Washington. There are
areas of cigs around 050-080.  The cigs should scatter out after
19Z. Isolated showers are possible over the mountains today, mainly
during the afternoon and evening hours.

KSEA...Clouds BKN045-070 should scatter out after 19z. MFVR cigs are
possible, but unlikely.  Southwest to south winds 4-8 knots. 13

&&

.MARINE...A weak ridge of high pressure over the coastal waters
will give westerly flow through the Strait of Juan de Fuca late this
afternoon.  The wind is expected to be just over 20 knots this
evening and a small craft advisory has been issued.

The surface ridge will move into the offshore waters Thursday
through Saturday resulting in a more west to northwest flow over the
coastal waters.  There is a chance that gale force westerly winds
will occur for a time Thursday evening and small craft advisory
conditions are possible in portions of the Northern Inland Waters.
Otherwise, small craft advisory conditions are expected through the
central and eastern portions of the Strait during the late afternoon
and evening hours. 13

&&

.SEW Watches/Warnings/Advisories...
WA...None.
PZ...Small craft advisory central and eastern strait.

&&

$$

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