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-- Discussion containing changed information from previous version are highlighted. --
000
FXUS66 KSEW 132155
AFDSEW

Area Forecast Discussion
National Weather Service Seattle WA
258 PM PDT Sat Apr 13 2024

.SYNOPSIS...Weak high pressure overhead through the weekend
bringing warmer and drier conditions. Upper-level troughing returns
on Monday with showers and cooler temps. Another ridge moves into
western Washington later in the upcoming week with the possibility
for more warm and dry weather.

&&

.SHORT TERM /TONIGHT THROUGH TUESDAY/...
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Current satellite imagery
shows low clouds have mostly dissipated with only mostly high clouds
moving northward over the area. As one would expect from the upper
level ridging in place, current radar remains clear.

As the upper level low that exited the area yesterday continues to
move southward, that is serving to wrap an upper level ridge from
mainly over the Rockies back westward into E WA and as such,
exerting its influence over the area today. By this evening, this
ridge shifts eastward allowing for the upper level ridge currently
over the Pacific to take over. No matter the source, the conditions
will remain the same for Sunday, continued warm temperatures and
mostly clear conditions. Highs today on track to hit the lower to
mid 60s this afternoon with water adjacent locations expected to be
a little cooler, in the mid to upper 50s. Daytime temps tomorrow
will be similar for the interior, but cooler for the western half of
the Olympic Peninsula, where the first hints of the incoming front
will be felt as temps there cool to the lower to mid 50s.

Models remain consistent on arrival of next frontal system Monday,
however it does seem like solutions are a little slower than 24
hours ago. Will need to keep an eye on this to see if 12Z data
follows this trend. As it stands now, will leave inherited forecast
in place, with some scattered moisture sneaking into the area as
early as late Sunday night while more widespread precip remains
likely to hold off until Monday morning along the coast and over the
Olympic Peninsula and Monday afternoon for the remainder of the CWA.
As to be expected, the front will drag high temperatures down into
the lower to mid 50s, which would be on average 2-4 degrees colder
than normal.

Tuesday sees the upper level trough slowly begin to exit the area.
Moisture with this feature remains spotting and as such PoPs for
much of the area will be on the low side...mainly within Slight
Chance range. The exception will be over the Cascades where the
combination of this moisture and the orographics will allow for
better chances for showers...but even then PoP only get into the 30-
50 pct range. High temps Tuesday look to be nearly identical to
those of Monday.

18

.LONG TERM /WEDNESDAY THROUGH SATURDAY/...Deterministic models in
agreement that an upper level ridge over the Pacific will intensify
starting Wednesday...but they disagree on how far inland its
influence will reach. GFS tends to keep it over the coastal waters,
actually allowing the exiting upper level low to stretch back into
the area while the ECMWF seems to be presenting the most likely
outcome as the ridge pushes inland, allowing for dry conditions to
return and another round of warming temperatures. Ensembles largely
favor this latter solution as well. NBM tries to split the
difference...keeping most of the area dry but still allowing the
upper trough centered over the middle of the country bring showers
to the Cascades. Really difficult to find justification for this
being included into the forecast, again given how lopsided support
for dry conditions is in the ensembles...but time enough to iron out
the noise with later runs. At least NBM solutions for Thursday night
into Friday seem to finally catch on and dry out the area
completely. Saturday remains a bit of a question mark as GFS brings
in a frontal system, ECMWF keeps the ridge in place and fizzles out
said front and ensemble members have yet to reach anything
approaching a consensus.

Warming temperatures will certainly be a highlight of the extended
forecast as highs Wednesday range from the upper 50s to lower
60s...although water adjacent sites will run a little cooler in the
lower to mid 50s. Thursday sees tepms largely in the mid 60s to
around 70 before topping out on both Friday and Saturday in the
upper 60s to lower 70s.

18
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&&

.AVIATION...
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Southwest flow aloft will transition more westerly into
Sunday with an upper low across California. VFR high clouds this
afternoon will continue at times into tonight. Onshore flow tonight
may result in lowering cigs along the coast into Sunday morning,
generally MVFR/IFR range. In addition, stratus may again develop in
Puget Sound, although confidence is low in this occuring. Patchy fog
may also occur, particularly towards western Whatcom County. Mainly
VFR again Sunday afternoon. North to northwest winds will become
lighter tonight.

KSEA...VFR cigs with high clouds at times into tonight. Another
round of stratus may be possible again Sunday morning, however
confidence is low, with generally a 15-20% chance of IFR cigs.
Otherwise, VFR cigs on Sunday. Northerly winds. JD
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&&

.MARINE...
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High pressure will continue through the weekend with Small
Craft Northwest winds along the Coastal Waters through Sunday. Winds
will then increase with a frontal system Sunday evening into Monday,
particularly for the Strait of Juan de Fuca and adjacent interior
waters, including Admiralty Inlet and the northern inland waters. A
Gale Watch has been issued for the central and eastern Strait of
Juan de Fuca with the increasing west winds. Northwest winds will
continue to remain breezy into Monday for the Coastal Waters with
this system. Winds will likely taper, but remain increased, for the
Strait of Juan de Fuca on Monday before another round of gales
possible Monday evening into Monday night. Winds look to ease
Wednesday into Thursday with building high pressure.

Seas will remain 7 to 11 feet through Monday with the highest waves
over the northern Coastal Waters. Waves will also be steep into
Sunday with a 9 to 10 second period. Seas will begin to subside
Tuesday and further Wednesday towards 4 to 6 feet. JD
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&&

.HYDROLOGY...No river flooding is expected through the next seven
days.


&&

.SEW WATCHES/WARNINGS/ADVISORIES...
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WA...None.
PZ...Gale Watch from Sunday afternoon through late Sunday night for
     Central U.S. Waters Strait Of Juan De Fuca-East Entrance
     U.S. Waters Strait Of Juan De Fuca.

     Small Craft Advisory until 11 PM PDT this evening for Coastal
     Waters From James Island To Point Grenville Out 10 Nm-
     Coastal Waters From Point Grenville To Cape Shoalwater Out
     10 Nm.

     Small Craft Advisory until 5 PM PDT Sunday 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.
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&&

$$