Small Craft Advisory 111, NWS Seattle, WA

Area Forecast Discussion
National Weather Service Seattle WA
830 PM PDT Wed May 3 2017

.SYNOPSIS...Warm weather on Thursday will give way to scattered
showers and thunderstorms by Thursday evening. A push of cool marine
air will occur Thursday night and showers will increase through
Friday as a cold front moves over Western Washington. A few showers
Saturday will give way to dry weather and a weak upper ridge early
next week.

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.SHORT TERM...There is a patch of clouds around the eastern part of
the Strait of Juan de Fuca this evening, otherwise skies are mostly
clear. Thursday will be a warm day with highs well into the 70s and
perhaps a few lower 80s in the warmest spots. The coast will see
marine air and cooling in the afternoon however, and areas of low
clouds will be developing along the coast. For the interior of
Western Washington, scattered thunderstorms should develop late
Thursday afternoon and then scattered showers will likely merge
and spread out into areas of rain Thursday night. The marine push
will cool and stabilize the air mass overnight. Showery cool weather
is on tap for Friday as the rest of a cold front moves ashore, and
then the showers should decrease on Saturday.

.LONG TERM...Some weak upper ridging should arrive later Sunday
and Monday for a dry break in the weather, though temperatures
will only warm back up to near normal for this time of year.

Yet another deep upper trough will carve out near 140W next
Tuesday and Wednesday, increasing our cooling onshore flow and
bringing an increasing chance of showers as the upper trough
starts to spread in our direction.  Haner

&&

.AVIATION...Southwest flow aloft will become more southerly on
Thursday as an offshore upper trough approaches. At the surface,
light northerly flow will prevail tonight and most of Thursday.
The air mass is generally dry and stable. Moisture will increase
on Thursday and it will become unstable. Scattered thunderstorms
are expected Thursday afternoon and early evening, mainly from
Puget Sound eastward.

KSEA...High clouds at times through Thursday morning. Mid clouds
will increase Thursday afternoon. There is a chance of
thunderstorms Thursday afternoon and early evening. Northerly wind
5-10 knots will switch to southerly early Thursday evening. MVFR
low clouds are likely later Thursday night. Schneider

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.MARINE...A weak thermal trough will be over the area tonight and
early Thursday with light northerly flow. An onshore push will
develop Thursday afternoon and evening. Small craft advisory west
wind are expected in the Strait and gales are possible. Moderate
onshore flow will continue on Friday as a cold front moves inland.
Onshore flow will prevail through the weekend. Schneider

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...None.
PZ...None.

&&

www.weather.gov/seattle

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