Area Forecast Discussion
Issued by NWS Seattle/Tacoma, WA

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FXUS66 KSEW 240306
AFDSEW

Area Forecast Discussion
National Weather Service Seattle WA
805 PM PDT Tue Oct 23 2018

.SYNOPSIS...A weak front will dissipate over the area allowing
southerly winds to clear out most of the fog that has been present
over Western Washington. Not much in the way of rainfall is expected
tonight and Wednesday. A stronger system will arrive on Thursday
with wet weather continuing into Friday. After a break on Saturday,
another front will reach the area on Sunday.

&&

.SHORT TERM...The weak front mentioned in the synopsis continues to
make its way over W WA this evening...dissipating as it does so.
With KATX down...radar echoes will be a bit less reliable...having
only the coastal radar to go by...but even with only that data can
infer that the projected weakening trend established by previous
model solutions is holding up quite nicely. Locations that do see
rainfall will likely only see minor amounts at best. And while the
influx of southerly surface winds may be helping the fog issue the
CWA has had over the past few days...moisture associated with this
passing front still will not do the area any favors as some dips in
visibility will still be possible. Inherited forecast suggests some
locations could dip down into 2-4 mile visibility and given the
fairly narrow temp/dewpoint spreads over much of the area...that
does not seem too far off.

With the exception of a few lingering showers in the mountains,
Wednesday should be mainly dry with a brief break in between
systems. Temperatures will warm a few degrees though cloud cover
will hang around. Next system arrives Thursday with precipitation
continuing into Friday. This appears to be a tad bit stronger and
wetter so more widespread accumulations are expected. Though track
of the center of the low will be NE into northern BC, breezy winds
look likely along the coast and north interior. SMR/CEO

.LONG TERM...From Previous Discussion...Ridging briefly builds in
the wake of departing system on Saturday with most areas seeing dry
weather. Models have slowed down the arrival of our next system so a
good portion of Sunday may end up being dry as well, but that
remains to be seen. Aforementioned system will then move across the
area Sunday night into Monday with showers likely continuing into
Tuesday. This system looks cooler than Thursday/Friday`s so snow
levels may drop to around 5000 feet. Temperatures will be near
normal. CEO

&&

.AVIATION...An upper level trough and dissipating surface front will
shift east of the region later tonight. A warm front associated with
the next stronger system will stall off the Washington coast
Wednesday afternoon into Thursday. Light to moderate southwest flow
aloft. Stable air mass, and becoming moist at all levels this
evening. Light spotty rain will be possible...mainly focused east of
the Sound and over the Cascades. Mostly VFR conditions expected this
evening but areas of MVFR will be possible given the residual near
surface moisture still lingering from fog earlier today. Low MVFR
cigs/vis will become more widespread later tonight into Wednesday
morning as moisture settles into a stable air mass.

KSEA...Most shower activity is in the process of moving east of the
terminal and is expected to end by midnight tonight. Southerly wind
6-10 kt. A mix of VFR and MVFR this evening with multiple cloud
layers as the dissipating front continues to move east and residual
low level moisture. Low MVFR cigs becoming more likely after
midnight through Wednesday morning, with brief IFR fog also possible
mainly after 12z tonight.  SMR/DTM

&&

.MARINE...Small craft advisory winds remain in place over the
coastal waters...although winds have subsided in the south Sound. As
such...will allow the SCA covering the latter area to expire while
keeping the coastal waters portion active with evening forecast
package.

Not much of a break is expected though as the next stronger system
will affect the waters as early as Wednesday afternoon and continue
through Thursday night. A warm front will reach the coastal waters
Wednesday afternoon and stall offshore through much of Thursday. A
couple of surface waves along the front will cause pressure
gradients to tighter at times, with southerly winds possibly
reaching near 30 kt off the coast. South to southeast winds will
also increase over the interior waters, especially from near the
east entrance to the Strait to the northern inland waters. Small
craft winds will be possible in these areas by Thursday and Thursday
night. All of that being said...will likely pull the trigger on
appropriate headlines with the morning forecast package. Winds
should ease later on Friday into Saturday between systems. SMR/DTM

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...None.
PZ...Small Craft Advisory until 11 PM PDT this evening 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.

&&

$$

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