Forecast Discussion for SEW NWS Office
000
FXUS66 KSEW 230613
AFDSEW

Area Forecast Discussion
National Weather Service Seattle WA
1013 PM PST Fri Feb 22 2019

.SYNOPSIS...A cool upper level trough will move down over Western
Washington tonight and remain over the area through the weekend.
The trough will keep showers in the forecast with daytime highs
remaining well below normal. A system moving up from the south may
bring more lowland snow to the region late Sunday night and
Monday.

&&

.SHORT TERM /TODAY THROUGH MONDAY/...Satellite imagery shows
mostly cloudy skies over Western Washington this evening. Doppler
radar still has a convergence zone over most of Snohomish county
at 9 pm/05z. Across the remainder of the area showers are
scattered with the northwesterly flow aloft causing a rain shadow
for the central and southern Puget Sound. Temperatures at 9 pm
were in the mid 30s to lower 40s.

Nothing new in the short term in the 00z model runs with a cool
upper level trough remaining over the area tonight through the
weekend. Snow levels will remain low, a 1000 feet or less, but
showers will be scattered. The best chances for seeing snow in the
lowlands will be on the higher hills in the late night and
morning hours. Showers decreasing Saturday night into Sunday as
the trough weakens over the region. Fraser river outflow winds
beginning Saturday night but with the model peaking the Bellingham
to Williams Lake gradient in the -15 to 18 mb range not expecting
any advisory level winds for Whatcom county. Highs will remain
well below normal, in the lower 40s for the most part. With a
little clearing in the early morning hours some locations will
drop below freezing. Most locations will end up in the upper 20s
to mid 30s both Saturday and Sunday morning.

The big forecast issue for the weekend will be the chances for
lowland snow late Sunday night into Monday. The 00z models so far
are of little help with the GFS solution keeping the precipitation
south of the area while the NAM lifts the front far enough north
Monday into Monday night with a few inches of snow over the Puget
Sound and the potential for a significant snow event over the
Southwest Interior. End of February? Will see what the 00z ECMWF
has to say, but with the lack of consistency in the solutions a
broad brush forecast will be the way to go until we get closer to
the event.

No changes to the forecast this evening. Snow showers have
diminished in the Cascades but with a convergence zone and another
batch of showers arriving in a couple of hours will keep the
advisory up through the early morning hours. Felton


.LONG TERM /TUESDAY THROUGH FRIDAY/...Showers will continue
through the rest of the week as an upper level trough stalls
offshore then shifts inland. Guidance shows we will remain a few
degrees below normal through the period. Snow levels will be
higher, mostly in the 1,000-2,000 ft range, for rain in the
lowlands. We may see a break in the action toward the end of the
week as a ridge builds in. 33

&&

.AVIATION...Northwesterly flow aloft becoming more westerly late
Saturday as upper level trough settles into the area. Weak low
level onshore flow will turn light offshore on Saturday. With the
light onshore gradients ceilings overnight in the 1000-2500 foot
range with higher ceilings over the northern portion of the area.
Conditions not changing much through the morning hours. Improving
trend Saturday afternoon with ceilings lifting up into the
4000-5000 foot range.

KSEA...Ceilings in the 1000-1500 foot range into the morning
hours. Some improvement late Saturday morning with ceilings
lifting up to around 4000-5000 feet in the afternoon.

Southerly winds 4 to 8 knots becoming southeasterly late Saturday.
Felton

&&

.MARINE...Winds continuing to ease overnight in the wake of
Friday`s front. Still some small craft advisory westerlies in the
central and Eastern Strait of Juan de Fuca. Small craft west
northwesterly winds also over the outer coastal waters tonight.
Low level flow turning weak offshore during the day Saturday into
Sunday morning as a weak surface low offshore moves south to off
the Oregon coast. Fraser river outflow winds developing Saturday
night but will be confined to the Northern Inland Waters. Low
level offshore flow will continue into Tuesday with high pressure
over British Columbia and lower pressure to the south of
Washington. Felton

&&

.HYDROLOGY...River flooding is not expected for the next 7 days.

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...Winter Weather Advisory until 6 AM PST Saturday for Cascades of
     Pierce and Lewis Counties-Cascades of Snohomish and King
     Counties-Cascades of Whatcom and Skagit Counties.

PZ...Small Craft Advisory for rough bar until 9 AM PST Saturday for
     Grays Harbor Bar.

     Small Craft Advisory until 4 AM PST Saturday 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.

&&

$$

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NWS SEW Office Area Forecast Discussion