Area Forecast Discussion
Issued by NWS Seattle/Tacoma, WA

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FXUS66 KSEW 122216
AFDSEW

Area Forecast Discussion
National Weather Service Seattle WA
316 PM PDT Tue Mar 12 2024

.SYNOPSIS...An upper level trough will slowly shift eastward over
the Pacific Northwest into tonight, with continued showers and
mountain snow. Upper level ridging will then build along the West
Coast Thursday through this weekend with building warmth and dry
conditions.

&&

.SHORT TERM /TONIGHT THROUGH FRIDAY/...Scattered showers across
portions of western Washington this afternoon with the main focus
turning towards a developing Puget Sound Convergence Zone
extending from northeastern Jefferson County eastward across
Whidbey Island into central Snohomish County. Another more
organized collection of showers and downpours can be found across
the southern Puget Sound. Several lightning strikes have also
occurred across the East Puget Sound lowlands near the Issaquah
Alps along the I-90 corridor of central King County earlier this
afternoon. Can`t rule out additional lightning strikes through the
remainder of the afternoon and evening with several hundred J/kg
of CAPE, especially in the developing convergence zone.

Light snow will continue through the Cascades, especially across
the central Cascades in association with convergence zone
enhancement. Thus, Winter Weather Advisories continue across the
central Cascades with an additional 2 to 6 inches of snow possible
with highest totals across King County, where totals could trend
a little higher wherever the convergence band sits the longest.
At this time that looks to favor the area near Stevens Pass more
so than Snoqualmie Pass. Opted to drop the Winter Storm Warning
for the north Cascades of eastern Whatcom and Skagit Counties as
the main synoptic-scale forcing for snow ends and any lingering
snow transitions mostly to convergence banding south of these
areas. Can`t rule out additional light accumulations, though
mostly sub- advisory amounts.

We begin to dry into Wednesday as upper-level ridging slowly
builds north and east into western Washington. A few more high
clouds look to pass over the region thanks to a weakening warm
front located offshore, which may enhance some light snow or
flurries over the Olympics and north Cascades, but it looks to be
a dry day for the most part. High temperatures inch upward a
degree or two closer to 50 across most of the lowlands.

The ridge continues to build eastward over the Pacific Northwest
Thursday and Friday with a thermal trough building along the
Oregon coast northward along the Washington Coast. Surface high
pressure building over the Canadian Rockies will help induce
offshore flow, which will help enhance adiabatic warming through
the Cascade and Olympic Valleys. High temperatures warm into the
low to mid 60s by Friday with partly to mostly sunny conditions.

.LONG TERM /SATURDAY THROUGH TUESDAY/...Upper-level ridging
continues Saturday and Sunday, reaching peak amplitude this
weekend with greatest potential for record high temperatures
across the lowlands. Nudged highs slightly towards the NBM 90th
percentile Saturday and Sunday due to continued offshore flow an
anomalously strong mid-level heights. Record highs this weekend in
the upper 60s to low 70s. Overall, a period of mild spring-like
weather is in store this week.

The ridge begins to break down into early next week with surface
low pressure tracking into British Columbia and dragging a weak
front across western Washington. Moisture looks weak with this
system at this time with little to no rainfall.

Davis

&&

.AVIATION...Flow aloft will become west to northwesterly this
evening as an upper trough axis continues to make its way eastward
across Washington state. The air mass will remain moist and somewhat
unstable through this afternoon and evening with scattered
showers continuing across the region. Radar this afternoon shows
heavier showers associated with a Puget Sound Convergence Zone
extending across the central Sound, mainly into Snohomish County.
Hi- res guidance has this feature sinking southward into King
County and lingering through the evening, before dissipating into
the Cascades between 07-10Z. Expect overall shower activity to
diminish tonight as a building upper ridge offshore begins to move
toward the area. A mix of VFR/MVFR ceilings in scattered post-
frontal showers will continue through this evening, though could
see conditions briefly drop to IFR in any heavier shower activity
(especially within the vicinity of the PSCZ). Another round of
widespread MVFR ceilings expected to redevelop overnight into
Thursday as onshore flow continues and surface winds ease.

KSEA...A mixed bag of VFR and high end MVFR expected through
this evening as scattered showers continue. Hi-res guidance
indicates PSCZ activity should remain north of the terminal.
Showers will diminish late tonight with ceilings expected to
settle into a BKN- OVC025-035 layer. Surface winds S/SW 10 to 15
knots with a few higher gusts to 20 to 25 knots continuing through
the afternoon. Winds will ease towards 5 to 10 knots tonight.

14

&&

.MARINE...Winds will continue to ease through the end of today in
the wake of a frontal system, with seas hovering between 10 to 15
feet over the coastal waters. Small Craft Advisories will remain
in effect along the Strait of Juan de Fuca through tonight with
gusty post-frontal westerlies persisting this afternoon. High
pressure will build over the area waters Wednesday and move inland
on Thursday, calming conditions. A thermal trough of low pressure
will expand northward on Friday, bringing light offshore flow to
the coast and along the Strait. The trough is expected to move
inland over the weekend. Overall, expect tranquil conditions to
persist over the waters through the weekend.

Seas will gradually subside and fall below 10 feet late Wednesday
and then look to generally hover between 6 to 8 feet heading into
the weekend.

Gordon/Borth

&&

.HYDROLOGY...The Skokomish River remains in Minor Flood Stage this
afternoon due to heavy rainfall Monday across the southern slopes
of the Olympics. The river is forecast to drop below flood stage
later this afternoon or evening and continue to fall through the
week with an extended period of dry weather.

Davis

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...Winter Weather Advisory until 5 PM PDT this afternoon for
     Olympics.

     Winter Storm Warning until 11 PM PDT this evening for West
     Slopes North Cascades and Passes.

     Winter Weather Advisory until 11 PM PDT this evening for West
     Slopes North Central Cascades and Passes-West Slopes South
     Central Cascades and Passes.

PZ...Small Craft Advisory until 2 PM PDT Wednesday for Grays Harbor
     Bar.

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

     Small Craft Advisory until 2 AM PDT Wednesday for Central U.S.
     Waters Strait Of Juan De Fuca.

     Small Craft Advisory until 5 PM PDT this afternoon for Puget
     Sound and Hood Canal.

     Small Craft Advisory until 5 PM PDT Wednesday 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.

&&

$$


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