Area Forecast Discussion
Issued by NWS Seattle/Tacoma, WA
FXUS66 KSEW 242216
Area Forecast Discussion
National Weather Service Seattle WA
315 PM PDT Fri Mar 24 2017
.SYNOPSIS...An upper trough will bring showers and a slight chance
of thunderstorms this evening. Showers will decrease Saturday as the
trough shifts inland. Another system will bring rain on Sunday.
After showers Monday, Tuesday and Wednesday both look rainy, with
Thursday and Friday showery but drier.
.SHORT TERM...There is still much cloudiness around the area, and
showers are widespread. There have not been any lightning strikes
today, but instability is enough to keep a slight chance of
thunderstorms in the forecast through this evening. There might be
some less cloudy periods tonight, but overall it will remain mostly
cloudy, with overnight lows mostly in the lower 40s.
The upper trough over the area will maintain a chance of showers
into Saturday but the coverage will be less than today. Highs will
be mostly in the low to mid 50s. Showers will taper significantly
Saturday night as high pressure aloft briefly moves over the area.
Sunday morning is likely to be dry as well over most of the region.
Another frontal system will bring an increasing chance of rain
Sunday. This system is somewhat split and not too impressive but all
areas should see some rain. Rain will move onto the coast in the
morning. The interior will likely be dry until afternoon when rain
will arrive. Temperatures are forecast to be a few degrees lower
with highs around 50. Another upper trough moving through the region
will bring a showery pattern Monday. Sun breaks will allow highs to
climb back into the lower to mid 50s. Burke
.LONG TERM...Tuesday earlier had appeared to be at least somewhat
dry, but now both Tuesday and Wednesday have wet weather systems.
This is true of both the euro and GFS. Thursday will be showery as
an upper trough passes. Friday has a chance of being a dry day,
though the GFS is trying to bring another system in late in the day.
Temperatures will be around normal all four days. Burke
.AVIATION...An upper trough off the coast is expected to weaken and
move onshore Saturday. SW flow aloft over Washington becoming
westerly Saturday. Air mass moist and weakly unstable.
Areas of showers east of the offshore upper trough through this
evening then decreasing through Saturday as the trough moves inland.
Mainly VFR ceilings though dipping to MVFR in some showers. Breaks
in the cloud cover between the showers at times as well. The air
mass is unstable enough to maintain the thunderstorm threat through
about 02z this evening.
Ceilings likely to drop to the upper end of MVFR many areas 10z-18z
Saturday before improving to VFR the rest of the day Saturday.
KSEA...Primarily VFR ceilings tonight dipping to the upper end of
MVFR in passing showers. Ceilings likely to drop to around 030 12z
Saturday. The risk of any evening thunderstorms is no more than 10
percent. SSW winds in the 10 to 20 kt range to ease after 02z this
evening and continue southerly through Saturday morning for your
flight flow direction planning. Buehner
.MARINE...Weak high pressure is expected to build over the coastal
waters through Saturday with onshore flow easing. The next Pacific
frontal system is forecast to move onshore late Sunday. A following
frontal system is expected to arrive by Tuesday. Both of these
systems look relatively weak and gale force winds appear unlikely.
Another system approaching on Wednesday may be stronger and has the
potential to produce gale force winds for at least the outer coastal
.HYDROLOGY...River flooding is unlikely over the next 7 days.
PZ...Small Craft Advisory until 6 AM PDT Saturday for Coastal Waters
From Cape Flattery To James Island 10 To 60 Nm-Coastal
Waters From James Island To Point Grenville 10 To 60 Nm-
Coastal Waters From Point Grenville To Cape Shoalwater 10
To 60 Nm.
Small Craft Advisory for hazardous seas from 6 AM to 3 PM PDT
Saturday for Coastal Waters From Cape Flattery To James
Island 10 To 60 Nm-Coastal Waters From James Island To
Point Grenville 10 To 60 Nm-Coastal Waters From Point
Grenville To Cape Shoalwater 10 To 60 Nm.
Small Craft Advisory for rough bar until 6 AM PDT Saturday for
Grays Harbor Bar.
Small Craft Advisory until midnight PDT tonight for Admiralty
Inlet-Coastal Waters From Cape Flattery To James Island Out
10 Nm-Coastal Waters From James Island To Point Grenville
Out 10 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-Puget Sound and Hood Canal-West Entrance U.S.
Waters Strait Of Juan De Fuca.
Small Craft Advisory for hazardous seas from midnight tonight to
3 PM PDT Saturday for Coastal Waters From Cape Flattery To
James Island Out 10 Nm-Coastal Waters From James Island To
Point Grenville Out 10 Nm-Coastal Waters From Point
Grenville To Cape Shoalwater Out 10 Nm.
You can see an illustrated version of this discussion at