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000
FXUS66 KSEW 120347
AFDSEW

Area Forecast Discussion
National Weather Service Seattle WA
847 PM PDT Thu Apr 11 2024

.UPDATE...Satellite and radar show the upper level portion of the
front draped right across western Washington, with the surface
front behind, currently right along the coastline as it works its
way onshore. Radar and surface observations also show strong
shadowing from the Olympics, with no rain being reported from
north Seattle up to Skagit County, as well as through the Kitsap
Peninsula and west of Port Angeles. As the front continues to
shrug onshore, it will weaken and stratiform rain will devolve
into scattered showers through most of the evening into early
tomorrow morning. Have adjusted PoPs to reflect the current
trends, otherwise the forecast remains on track. See updates to
the aviation section below.

&&

.SYNOPSIS...A weakening cold front will bring showers inland
throughout tonight across western Washington. A weak ridge will
allow skies to clear late Friday afternoon into Saturday, with
highs well above normal. A series of systems will return the
chance of showers and cooler temperatures for next week.

&&

.SHORT TERM /TONIGHT THROUGH MONDAY/...Upper level analysis shows
a 300 mb trough positively tilted over the Pacific Ocean into
British Columbia/Alberta, with the center of the low off the coast
of Oregon/California. The low is expected to cutoff as it fills
over the Pacific, leaving western Washington in a zonal flow
pattern through the weekend (as the flow splits). At the surface,
a weakening cold front continues to approach the western
Washington coastline this afternoon.

A band of showers/light rain has been observed on radar moving
northeastward over the Pacific Ocean. As of early this afternoon,
showers have begun falling over the Olympics, and into Quillayute.
Coverage is expected to increase eastward this afternoon/evening
as the surface low pressure center tracks southward from British
Columbia, through Washington and into Oregon. The system is
expected to slow down coming onto land, which will keep
precipitation chances lingering through the first part of Friday.
Most of the rain will fall in the coastal areas/Olympics, with
potentially over half an inch of QPF possible. Remaining areas
will only see a tenth of two of an inch of QPF (though a possible
convergence zone over Snohomish County cannot be ruled out once
the front passes).

The remainder of this weekend looks dry with the zonal flow/weak
ridge setting up over Washington. Skies will gradually clear out
during the day Friday, and for most of Saturday. The warmest day
will be on Saturday, with widespread high temperatures in the mid
60s. A couple areas in the Southwest Interior may have a shot of
seeing 70 degrees (especially given the zonal flow). A few more
clouds will increase on Sunday as the zonal flow breaks down with
an approaching trough from the north. Temperatures outside of
Saturday will top out in the upper 50s to low 60s. Expect low
temperatures to drop into the 40s. Surface winds in this period will
remain light over land (around 5 mph), and will be out of the
southwest Thursday, and north Friday into Sunday.

.LONG TERM /TUESDAY THROUGH FRIDAY/...Ensembles/deterministic
models have the zonal flow breaking down on Monday, with a trough
digging down into Washington through the first part of the work
week. This will keep a chance of showers Monday through the first
part of Wednesday. There`s split confidence as to what happens
post Wednesday, but there seems to be more models leaning towards
some clearing and ridging behind the trough. Sunday/Monday`s front
may be a little breezy, but otherwise no significant winds are
expected in the long-term. High temperatures will take a dip into
the mid 50s Monday/Tuesday, before climbing back to the low 60s
Wednesday/Thursday.

HPR

&&

.AVIATION...Southwest flow aloft continues with weak front along
the coastline this evening moves inland and dissipates after
midnight. Low level flow turning northerly early Friday morning
and remaining northerly through the day.

MVFR ceilings along the coast. VFR ceilings over the interior
lowering to MVFR 07z-09z. Local IFR ceilings 12z-16z. Ceilings
improving to VFR 18z-20z with clouds scattering out 22z-00z.

KSEA...VFR ceilings lowering to MVFR around 08z. Possible IFR
ceilings 12z-16z. Ceilings improving around 18z with VFR ceilings
by 20z. Clouds scattering out after 22z. Southerly wind 4 to 8
knots becoming light northeast around 08z. Northerly wind 8 to 12
knots after 21z.

Felton

&&

.MARINE...A weak front will slowly shift inland and dissipate
tonight. Broad surface ridging will expand over the offshore and
coastal waters Friday and Saturday. This will lead to increasing
northerlies...some of which are expected to reach small craft
advisory speeds over the outer coastal waters. A frontal boundary
sliding southward over British Columbia later Sunday will produce a
sharp increase in onshore flow. This will likely lead to additional
headlines in the form of small craft advisory level winds for the
coastal waters and possible westerly gales in the strait Sunday
night. Surface ridging gradually rebuilds across the waters early
next week for a transition to quieter conditions.

A sustained period of northwest winds over the coastal waters this
weekend into early next week is expected generate hazardous seas in
the form of short period swell at times.

27

&&

.HYDROLOGY...River flooding is not expected over the next seven
days.


&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...None.
PZ...Small Craft Advisory from 5 PM Friday to 5 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.

&&

$$