Area Forecast Discussion
Issued by NWS Seattle/Tacoma, WA
FXUS66 KSEW 240411
Area Forecast Discussion
National Weather Service Seattle WA
915 PM PDT Thu Mar 23 2017
.SYNOPSIS...Rain will continue to spread over the area tonight as a
front slowly moves through Western Washington. An upper trough will
bring showers Friday. Showers will decrease Saturday as the trough
shifts inland. Additional fronts will reach the area Sunday and
.SHORT TERM...Rain associated with front slowly making its way
through the area is gradually creeping eastward. While the radar
certainly looks like most areas should be seeing precip...obs paint
a picture of more hit-or-miss activity...particularly along the
leading edge of radar echoes. The stronger returns out over the
western half of the CWA look to be more uniform and thus for the
eastern half of the CWA...will likely get this more stratiform
rainfall during the overnight hours. So anyone walking a four-legged
friend in these last moments of National Puppy Day had best do so
quickly...unless there is a desire for that wet dog smell.
Forecast models remain pretty consistent and therefore...forecast
remains fairly unchanged. Front passing through tonight while an
associated upper level trough will keep activity going over the area
through much of Friday. Instability with this upper level trough may
result in a slight chance for a few rumbles of thunder mainly
tomorrow afternoon. This may also result in some more snow for the
Cascades and as such...a Winter Weather Advisory remains in effect.
Overnight Friday and into Saturday afternoon will see activity
scatter out as a weak upper level ridge tries to make its way into
the region. Current runs are a little slower with this drying out
process compared to those 24 hours ago...which is a bit of a bummer.
Accentuating that is the fact that models remain consistent on the
follow-up feature...bringing rain to the coast by mid-morning Sunday
and spreading inland by late Sunday afternoon in what appears to be
deja-vu of current system. As such, front pushes through and exits
the area early Sunday evening followed by upper level trough that
allows for rain to continue into Monday. SMR
.LONG TERM...From previous discussion...Monday will be showery as an
upper trough passes. Tuesday now looks wetter in the models and have
boosted pops, especially on the coast and in the mountains.
Wednesday still appears to be a day when a front brings rain.
Thursday will be showery at first but could see significant drying
later in the day. Temperatures will be close to normal through the
.AVIATION...Strong southwest flow aloft over Western Washington
this evening will continue tonight and Friday, as the frontal system
moving through the region is followed by an upper trough.
The air mass will be moist and slightly unstable.
Rain associated with the incoming frontal system is spreading into
Western Washington this evening with ceilings generally 035-060.
Conditions should deteriorate slightly tonight as rain continues,
but we are expecting ceilings to remain generally in the low-end VFR
range. Conditions will improve only marginally on Friday as an upper
trough follows the front, with scattered showers and a slight chance
of thunderstorms during the afternoon and evening.
KSEA...South to southwest wind 6-10 kt should increase to 8-14 kt
during the next few hours and continue through Friday; there should
be some gusts to around 22 kt. VFR cigs generally 035-050 with the
front tonight and the post-frontal trough on Friday.
There is a 20 percent chance of a thunderstorm in the vicinity of
KSEA Friday afternoon or evening. McDonnal
.MARINE...A vigorous Pacific frontal system over the coastal
waters this evening will move across Western Washington tonight.
The front should produce gales over the coastal waters, at the east
entrance Strait of Juan de Fuca, and in the northern inland waters.
A trough will follow the front on Friday, and we should have at
least marginal small craft advisory winds for most of the coastal
and inland waters. Weak high pressure will move across the region
Saturday for lighter winds. The next frontal system will move
through the area Sunday night, with another front approaching on
Tuesday. Both of these systems look relatively weak, with gales
.HYDROLOGY...River flooding is unlikely over the next 7 days.
WA...Winter Weather Advisory until 11 AM PDT Friday for Cascades of
Pierce and Lewis Counties-Cascades of Whatcom and Skagit
PZ...Small Craft Advisory from 3 AM Friday to 5 AM PDT Saturday 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-East Entrance U.S.
Waters Strait Of Juan De Fuca-Northern Inland Waters
Including The San Juan Islands.
Gale Warning until 3 AM PDT Friday 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-East Entrance U.S. Waters Strait Of Juan De Fuca-
Northern Inland Waters Including The San Juan Islands.
Small Craft Advisory for rough bar until 11 PM PDT Friday for
Grays Harbor Bar.
Small Craft Advisory until 5 AM PDT Saturday for West Entrance
U.S. Waters Strait Of Juan De Fuca.
Small Craft Advisory until 6 AM PDT Friday for Central U.S.
Waters Strait Of Juan De Fuca.
Small Craft Advisory until 5 PM PDT Friday for Admiralty Inlet-
Puget Sound and Hood Canal.
You can see an illustrated version of this discussion at