Area Forecast Discussion
Issued by NWS Seattle/Tacoma, WA

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FXUS66 KSEW 241029
AFDSEW

Area Forecast Discussion
National Weather Service Seattle WA
330 AM PDT Mon Apr 24 2017

.SYNOPSIS...Showery weather will continue for much of the
upcoming week as a series of weather systems move through. There
should be a dry spell Monday night and the first part of Tuesday
as high pressure aloft crosses the area. Another dry period is
likely Friday and Saturday.

&&

.SHORT TERM...Current satellite and radar imagery line up fairly
well with GFS initializations this morning as upper level low sets up
shop just over the far northwestern tip of the state this
morning...and as such showers remain generally confined to the coast
and the southwestern quarter of the CWA. Progs have this system
dipping further south this afternoon before finally moving eastward
this evening. The southward dip is what will allow moisture to be
drawn up and thus spreading the threat of showers to much of the
area early this afternoon. Once the low starts moving east it is
game over as precip is expected to taper off pretty quickly with dry
conditions setting up in most places before midnight tonight.

Upper level ridging will take over during the overnight period and
into Tuesday morning. As usual...the relief proves brief as a front
associated with upper level low pressure to the north makes its way
onto the coast by mid-afternoon...spreading precip eastward reaching
most locations by Tuesday evening. Shortwave disturbances in the
flow look to keep shower activity locked over the area into
Wednesday. It would be nice to point out that it looks like showers
will become more scattered in nature Wed afternoon and evening...GFS
model runs have been going back and forth between wet solutions and
dry solutions every other run while the ECMWF...as usual...favors a
wetter scenario. Clinging desperately to the hope that this active
pattern will eventually end...so have opted to side with drier GFS
solutions.

The upper low will shift eastward Thursday...ramping up precip yet
again and resulting in continued wet conditions.

Temperatures in the near term look to hover in the lower to mid 50s
as the mix of precip and clouds prove to be a pretty big hurdle to
overcome as the quest to return to 60 slogs on.  SMR

.LONG TERM...As the aforementioned upper low continues to move east
Thursday evening showers look to taper off. Models remain consistent
in an upper level ridge following this feature and dry conditions
look to be on tap for Friday and into Saturday morning. Models
diverge here with...shockingly...the ECMWF keeping conditions dry
for the bulk of the day Saturday while the GFS is more progressive
with yet another upper level low. Both models have some showers in
for Sunday thanks to the low from the previous sentence and also
continue to advertise a light at the end of the tunnel with an upper
level ridge over the area for the first half of next week. Would
absolutely love to bite on to this solution...but 24 hours ago
models were suggesting this ridge for the upcoming weekend. This
brings forth the question...have the models just shifted their
timing...or have they adopted a stick-and-carrot philosophy to lead
forecasters to their doom. Needless to say...will be curious as to
what models will advertise 24 hours from now. SMR

&&

.AVIATION...An upper level low will move from Western Washington
to eastern Oregon today. Meanwhile, a surface low will move by to
our south this morning. Moderate southwest flow aloft will become
light and variable later this morning, then become light
northwesterly tonight. The air mass will be moist and somewhat
unstable through this morning, then the air mass will become a
bit more stable with a shallowing of the moist layer late today.

KSEA...Will be near the northern fringe of a widespread area of
rain today. The air mass will be richly moist through tonight, so
mere thinning of cloud layers is expected. Northerly surface flow
for much of today will lead to some modest drying and scattering
of clouds. A return to S-SW surface wind this evening will spell
a quick return to a richly moist low- level environment, along
with a return of clouds at or below 020. Haner

&&

.MARINE...A 1001 mb surface low will move eastward onto the north
Oregon coast this morning, then move east of the Cascades this
afternoon. A weak surface ridge will drift across the waters early
Tuesday. On Tuesday night, an occluded front will cross the
waters. Following Tuesday night`s front, strong onshore flow will
develop from Wednesday through Friday, with westerly gales
possible in the central and eastern Strait of Juan de Fuca. Haner

&&

.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



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