Area Forecast Discussion
Issued by NWS Seattle/Tacoma, WA

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505
FXUS66 KSEW 191036
AFDSEW

Area Forecast Discussion
National Weather Service Seattle WA
330 AM PDT TUE JUL 19 2016

.SYNOPSIS...An upper low off the coast will bring a slight chance
for showers over Western Washington through this evening with
isolated thunderstorms over the Cascades. The low will weaken as it
moves slowly inland Wednesday, and the threat of showers will
decrease as a weaker trough sits well offshore. A weak upper ridge
should bring dry and warmer weather this weekend.

&&

.SHORT TERM...Current radar and IR satellite imagery showing a quiet
start to the day today. While the upper low responsible for showers
and isolated thunderstorms yesterday lingers...will likely start to
see some redevelopment as we get into late morning or early
afternoon today. Sufficient instability for thunderstorms does not
look to be as widespread as it was yesterday...generally keeping to
the Cascades and associated foothills. However...some low end
instability will be present...likely just enough to help break up
some of the clouds for some breaks of sunshine in the late afternoon
and early evening.

The low weakens significantly through the day Wednesday...allowing
for an upper level ridge over eastern Washington to start exerting
some influence. This will result in mostly dry conditions continuing
in to early Thursday. Getting into Thursday
afternoon...however...looks like the upper low and associated upper
level trough finally push inland bringing another round of
showers...some of which might linger into Friday.

.LONG TERM...A fairly unimpressive ridge builds into the area
starting Friday evening and into Saturday before flattening out into
zonal flow Sunday. Monday and into early Tuesday have a minor ridge
that really looks no better than a hiccup followed by an equally
minor shortwave late Tuesday and into Wednesday. Models prog this
shortwave to be dry...so long term forecast overall looks to be
rather snooze-worthy.  SMR

&&

.AVIATION...A broad upper low over the coastal waters will remain
stationary through today giving light southwest flow aloft. A ridge
of high pressure extending northward from the Oregon coastal waters
along the Washington coastline will give low level south to
southwest flow. The air mass will be moist through today. The lower
levels will be mainly stable with a marine layer.

A few showers remain, mainly near western Whatcom county early this
morning. Stratus has filled in over most locations with ceilings
falling to around BKN-OVC030-050. Lower stratus will likely scatter
out around 20Z today.

KSEA...Clouds around SCT-BKN040 this morning, could fall to about
BKN015-020 early this morning. The lower layer should scatter out or
lift around 20z. Winds will be southerly 4-8 KT. 13

&&

.MARINE...A weak ridge of high pressure extends from the Oregon
coastal waters northward into the Washington coastal waters. This
will result in southerly flow over the coastal waters and southwest
flow inland. Onshore flow will weaken by Wednesday.

The surface ridge will move into the offshore waters later Wednesday
through Friday resulting in a more west to northwest flow over the
coastal waters. Expect daily inflow through the Strait of Juan de
Fuca resulting in typical late afternoon and evening  small craft
advisory conditions Thursday through Saturday. 13

&&

.SEW Watches/Warnings/Advisories...
WA...None.
PZ...None.

&&

$$

www.weather.gov/seattle

You can see an illustrated version of this discussion at
www.weather.gov/seattle/gafd/latest_webafd.html



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