National Weather Service Text Product Display

Area Forecast Discussion
Issued by NWS Seattle/Tacoma, WA
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FXUS66 KSEW 010456
AFDSEW

Area Forecast Discussion
National Weather Service Seattle WA
856 PM PST Tue Jan 31 2017

.SYNOPSIS...Expect dry north flow over Western Washington through
Thursday with an upper level ridge offshore. The ridge will
dissipate on Friday with a weather system moving up from the south
during the day. Unsettled weather will continue into the first
part of next week with an upper level trough in the vicinity.

&&

.SHORT TERM...Offshore flow will continue through Thursday for
dry but cool weather across the area. Temperatures will drop into
the 20s to lower 30s tonight with highs in the lower 40s on
Wednesday. It will be cooler Wednesday night with temperatures
down in the teens in a few spots, like Olympia and Shelton.
Expect lots of sunshine though.

An upper level low spinning offshore will spread moisture north
into Western Washington late Thursday night into Friday. This
front is weak and precipitation amounts are light. However, at
this point, the low level air mass will still be cool enough to
support a chance of lowland snow. A light dusting is possible but
most areas, including Seattle, may only see a trace if anything at
all. The air mass will moderate Friday afternoon with snow levels
rising to around 1500 feet. Temperatures will rise to the lower to
mid 40s with mainly light rain expected. Showers will continue
Friday night but temperatures should stay above freezing. 33

.LONG TERM...Previous discussion...System moves through Friday
evening with southwesterly flow aloft continuing. Large upper
level low setting up off the British Columbia coast on Saturday
and Sunday with southwesterly flow aloft continuing over the area.
Timing of the systems spinning out of the low tough at this point
so for now there is a broad brush chance of rain or rain likely
forecast for Saturday and Sunday.

12z extended models much colder for the first part of next week
with the models showing the possibility of a lowland snow event.
Confidence in this solution is very low at this time especially
with the departure of the 12z solutions from the previous model
runs. Have cooled down the high temperatures a few degrees for
Monday and Tuesday and lowered the snow levels a bit but still
have the precipitation type as rain in the lowlands. Felton

&&

.AVIATION...Northwest flow aloft will prevail tonight and
Wednesday. At the surface, northeasterly offshore flow will
increase as high pressure builds over southern British Columbia.
The air mass is dry and stable. Although most locations in Western
Washington reporting clear skies this evening...some lingering VFR
low clouds remain over the south interior and near the
Cascades...but those should scatter out by late tonight.

KSEA...Mostly clear tonight and Wednesday. Northerly wind 8-12 knots
tonight and overnight. North to northeast wind will increase to 15
to 20 knots on Wednesday. Schneider/SMR

&&

.MARINE...Increasing northeast offshore flow will bring small
craft advisory winds to most waters for the next few days. Gales
are likely for the outer Coastal Waters later Wednesday into
Thursday morning. A gale watch has been issued and remains in place.
So long as models remain consistent...and no reason why they should
deviate now...will likely upgrade watch to a warning for the early
morning forecast package.

The forecast is currently 20-30 knots for the Northern Inland
waters and Strait of Juan De Fuca Wednesday through the first part
of Thursday. That said, gales are also possible...but not as
likely...for these areas. Will re-evaluate this with incoming 00Z
model data as models have waffled a bit on this.

Offshore flow will begin to ease and turn more easterly later
Thursday as high pressure over British Columbia moves off to the
southeast. A frontal system will move through the waters Friday
and Saturday. Another surface trough will affect the waters on
Sunday. Schneider/SMR

&&

.HYDROLOGY...No river flooding is expected in the next 7 days.

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...None.
PZ...Gale Watch from Wednesday afternoon through Thursday morning 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 until 4 PM PST Wednesday for Central U.S.
     Waters Strait Of Juan De Fuca-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-East
     Entrance U.S. Waters Strait Of Juan De Fuca-Northern Inland
     Waters Including The San Juan Islands-Puget Sound and Hood
     Canal.

     Small Craft Advisory until 4 PM PST Wednesday 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-
     West Entrance U.S. Waters Strait Of Juan De Fuca.

     Small Craft Advisory until 9 PM PST this evening for Admiralty
     Inlet.

&&

$$

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