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-- Discussion containing changed information from previous version are highlighted. --
000
FXUS66 KSEW 250418
AFDSEW

Area Forecast Discussion
National Weather Service Seattle WA
918 PM PDT Fri Mar 24 2023

.SYNOPSIS...
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A cool and active weather pattern will remain over
Western Washington through the weekend. Scattered showers and
possibly a Puget Sound Convergence zone in place for tonight.
Lowland locations will see chances of precipitation gradually lower
over the weekend while mountain snow showers are expected to
persist. Lingering cold temperatures will during the overnight and
early morning hours may bring a rain/snow mix both Saturday and
Sunday. Drier weather is in store early next week.
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&&

.SHORT TERM /TONIGHT THROUGH MONDAY/...
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Still seeing showers in place
over portions of W WA this morning. Trends are not really showing
much in the way of a decrease in coverage, however precip intensity
has dwindled since this afternoon. There appear to be hints of a
PSCZ over portions of northern King and southern Snohomish counties
which will likely boost snowfall amounts over the current Winter
Weather Advisory area. Some reports of mixed precip and/or snow
showers came in during the late afternoon from northern locations
such as in Whatcom county...likely due to both the cooler
temperatures already in place there as well as cooling from higher
intensity echoes. At this time however, not seeing much in the way
of snowfall either via current obs or from reports. The prospect for
such will a concern for some lowland locations, but at least for
tonight is not expected to be widespread nor will there be any
accumulations.

Inherited forecast looks on track and as such, no evening update is
needed. For forecast details, please refer to the Previous
Discussion section below.  18

From Previous Discussion...Scattered showers over the area this
afternoon will continue into this evening. There remains a chance of
isolated thunderstorms with this - especially along the coast and
interior south of Puget Sound. Increasing onshore flow will elevate
odds of the formation of a Puget Sound Convergence zone late this
afternoon and evening. Have included a chance of thunder over
Snohomish and King Counties this evening to reflect the possibility
of seeing lightning with the convergence zone if it forms. In
addition, both the HREF and UW HiRes ensemble systems continue to
show the possibility of persistent or heavier showers in the
convergence zone lowering the snow level - resulting in some snow
mixed in with convergence zone rain tonight.While impacts aren`t
expected, they remain possible and folks traveling should be aware
of the possibility. Ensemble members that do develop a convergence
zone show it developing late this afternoon/early evening - between
the I-90 corridor in King County northward to US-2 in Snohomish
County. In addition, the cooler air mass over the region through the
weekend will help lower snow levels to below 1000 feet during the
late night/early morning hours going into Saturday and again going
into Sunday. This will allow for a broader potential for a rain/snow
mix or even just snow showers at those times - very limited
accumulations, if any at all, are possible.

Sunday will trend drier but with the broad trough still over the
region, showery weather will remain over the area - especially the
higher terrain. Even so, as is typical for this time of year -  even
a few cloud breaks could boost high temps Sunday just north of 50
for many areas in the interior.

Monday will see an upper level shortwave trough that has moved down
the British Columbia Coast slide southward well to the west of
Washington. This may provide some boost to clouds and even some
light precipitation for Western Washington - but in general the idea
is for another benign, mostly dry day Monday.

.LONG TERM /TUESDAY THROUGH FRIDAY/...From Previous
Discussion...Ensembles from the ECMWF, GEFS and CMC systems
consistently show the offshore upper level trough strengthening as
it digs southward over the Eastern Pacific before moving onshore
somewhere over Southern Oregon into Northern California Monday into
Tuesday. This also equates to the some degree of upper level ridging
and drier weather building in over the Pacific Northwest midweek.
Some potential for offshore low level flow will help with less cloud
cover high temperatures near normal - in the mid 50s. The pattern
may weaken late in the week opening the door for a potential return
of at least Spring showers toward the latter half of the week.
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&&

.AVIATION...
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Light flow aloft through Saturday with low level
onshore flow. Air mass unstable with upper level trough overhead.

Ceilings mostly 2000 to 3000 feet into Saturday afternoon.
Convergence zone over Northern King and Southern Snohomish county
dissipating Saturday morning. Ceilings near 1000 feet in
convergence zone. Thunderstorms possible along the coast
Saturday.

KSEA...MVFR ceilings through Saturday afternoon. Southerly winds 8
to 12 knots easing to 4 to 8 knots Saturday morning. Felton
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&&

.MARINE...
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Small craft advisories over most of the waters
overnight. Winds easing over the interior with small craft
advisory winds continuing over the coastal waters into Saturday
night. High pressure building well offshore and lower pressure
over the interior will continue to produce onshore flow through
the weekend. The flow will then turn offshore early next week as a
surface low digs southward over the offshore waters. Seas 12 to
16 feet across the coastal waters will slowly subside Saturday and
Saturday night before subsiding back below 10 feet Sunday. Low
level flow turning offshore first part of next week. Felton/27
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&&

.HYDROLOGY...
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No river flooding the next 7 days.
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&&

.SEW WATCHES/WARNINGS/ADVISORIES...
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WA...Winter Weather Advisory until 5 AM PDT Saturday for West Slopes
     North Central Cascades and Passes-West Slopes South Central
     Cascades and Passes.

PZ...Small Craft Advisory until 6 AM PDT Sunday for Coastal Waters
     From Cape Flattery To James Island 10 To 60 Nm-Coastal
     Waters From Cape Flattery To James Island Out 10 Nm-Coastal
     Waters From James Island To Point Grenville 10 To 60 Nm-
     Coastal Waters From James Island To Point Grenville Out 10
     Nm-Coastal Waters From Point Grenville To Cape Shoalwater
     10 To 60 Nm-Coastal Waters From Point Grenville To Cape
     Shoalwater Out 10 Nm-Grays Harbor Bar.

     Small Craft Advisory until 5 PM PDT Saturday for West Entrance
     U.S. Waters Strait Of Juan De Fuca.

     Small Craft Advisory until 5 AM PDT Saturday 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 Northern
     Inland Waters Including The San Juan Islands.

     Small Craft Advisory until 6 AM PDT Saturday for Admiralty Inlet.

     Small Craft Advisory until midnight PDT tonight for Puget Sound
     and Hood Canal.
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&&

$$