Area Forecast Discussion
Issued by NWS Seattle/Tacoma, WA
FXUS66 KSEW 241537
Area Forecast Discussion
National Weather Service Seattle WA
840 AM PDT Fri Mar 24 2017
.SYNOPSIS...An upper trough will bring showers and a slight chance
of thunderstorms today and this evening. Showers will decrease
Saturday as the trough shifts inland. The pattern will remain fairly
wet into the middle of next week as a series of weather systems move
through the area.
.SHORT TERM...Radar and satellite imagery indicate a front has moved
east of Puget Sound, leaving a more showery pattern behind. Visible
satellite picture indicates there should be at least some clearing
today, though a cumulus field is likely to fill in the clear areas
and there will be showers as an upper trough remains over the
region. The air mass will be unstable enough for a slight chance of
thunderstorms this afternoon and early evening. Snow has tapered on
the volcanoes and the winter weather advisory in the Cascades will
be allowed to expire at 11 AM. Snow will continue at times in
showers. Highs today will be mainly in the lower to mid 50s.
Showers will taper tonight and become somewhat confined to the
mountains and coast with the loss of daytime heating. The upper
trough over the area will maintain a chance of showers into Saturday
but the coverage will be less than today. 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. Burke/Schneider
.LONG TERM...Previous discussion...An upper trough will shift east
of the area Monday for decreasing showers but there won`t really be
any break in the wet weather as warm front rain from the next
frontal system will already be moving into the area in the
afternoon. The warm front should result in a drippy Monday night. A
trailing cold front will keep rain chances high on Tuesday and
Wednesday. Drier weather is expected on Thursday as an upper ridge
builds over the Northeast Pacific. Schneider
.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 today into this
evening. Mainly VFR ceilings though dipping to MVFR in some showers.
Sunbreaks between the showers at times as well. The air mass is
unstable enough that any warmer sunshine may help develop an
isolated thunderstorm from about 20z-02z. Afternoon convective
temperatures will run from about 47 to 51 deg. Decreasing showers
after sundown this evening but continuing and more widely scattered
into Saturday morning.
KSEA...Primarily VFR ceilings today dipping to the upper end of MVFR
in passing showers. The risk of any afternoon thunderstorms is no
more than 20 percent. SE winds this morning should become S to SW by
18z and pick up this afternoon to 10 to 20 kt before easing after
.MARINE...A 992 mb low 350 nm west of Cape Flattery will continue
tracking north into the central British Columbia coast today. Weak
higher pres to build over the coastal waters through tonight and
Saturday. Onshore flow into Western Washington today to weaken
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. Buehner
.HYDROLOGY...River flooding is unlikely over the next 7 days.
WA...Winter Weather Advisory until 11 AM PDT this morning for
Cascades of Pierce and Lewis Counties-Cascades of Whatcom
and Skagit Counties.
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