Area Forecast Discussion
Issued by NWS Seattle/Tacoma, WA

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000
FXUS66 KSEW 120934
AFDSEW

Area Forecast Discussion
National Weather Service Seattle WA
234 AM PDT Tue Mar 12 2024

.SYNOPSIS...Upper troughing will move across the area through
today for continued showers and mountain snow. Ridging will begin
to build offshore Wednesday. The upper ridge will be located
across the Pacific Northwest through the weekend for dry, warmer
weather.

&&

.SHORT TERM /TODAY THROUGH THURSDAY/...An upper level trough will
slowly progress eastward through today for continued convective
showers across western Washington. Increasing onshore flow will
also allow for the development of a convergence zone generally
across Snohomish and northern King County this afternoon into this
evening. In addition, at least some instability (200-300 J/kg) may
result in a few isolated thunderstorms today, with the threat
diminishing later this evening. Snow levels today will range 2000
to 3000 feet resulting in continued snow accumulation for the
Cascades, including Stevens and Snoqualmie Pass. Generally another
8-10" is expected for the Passes, with localized heavier snowfall
amounts in areas of convergence later today.

The upper trough will move east of the area tonight with ridging
building offshore of western Washington. Precipitation potential
will diminish for much of the area later tonight into Wednesday
morning, with some lingering showers possible, especially in the
Cascades with a period of NW winds aloft. The ridge will build
further in extent into western Washington later Wednesday into
Thursday for drier conditions and warming temperatures. Clouds
will likely be around for a good portion of Wednesday before
clearing Wednesday night into Thursday, other than areas of fog
during the morning hours on Thursday. Highs will slowly warm into
the mid to upper 50s by Thursday.

.LONG TERM /FRIDAY THROUGH MONDAY/...An impressive upper ridge
will be the main theme for western Washington during this period,
resulting in dry conditions and warm temperatures. Offshore
flow will increase later this week, and likely peak later Friday
and into early Saturday. Temperatures will range in the low to mid
60s on Friday, however, areas in the Cascade Valleys, as well as
western slopes of the Olympics (such as Forks) may reach near 70
due to increased easterly flow. The warmest days for most areas
will likely be Saturday and Sunday with the ridge axis overhead.
NBM suggests a 40-70% of 70 degrees for areas away from the water
across the interior both days, with the highest probabilities in
the Cascade Foothills and south of Olympia. At this time, the best
potential for record breaking max temps is at KUIL, but have
trended towards 50PCT NBM for the forecast which suggests KBLI and
KHQM may reach record temperatures as well. All this is semantics
of course, as this will be a beautiful March weekend across
western Washington. Onshore flow may increase on Monday, but
continued dry weather and warmer temperatures are expected across
the area. JD

&&

.AVIATION...Southwest flow aloft will become west to
northwesterly this afternoon as an upper trough axis shiftearly
spring seasons onshore over Western Washington. The air mass will
remain moist and somewhat unstable today with scattered showers
across the region. Showers will diminish tonight as a building
upper ridge offshore begins to move toward the area. A typical mix
of VFR/MVFR ceilings in scattered post-frontal showers will be
the story today. Ceilings will likely settle into predominantly
MVFR tonight as onshore flow continues and surface winds ease.

KSEA...A mixed bag of VFR and tempo MVFR in scattered showers
expected today. Showers diminish tonight with ceilings expected to
settle into a BKN-OVC025-035 layer. Surface winds S/SW 8 to 12 knots
with a few higher gusts primarily morning hours. Winds easing
further tonight.  27

&&

.MARINE...Small craft advisory conditions continuing today as
onshore flow continues in the wake of yesterdays frontal system. A
surface ridge will amplify over the coastal waters on Wednesday
before shifting inland on Thursday. A thermally induced trough of
low pressure will expand northward along the coast on Friday for
offshore flow. The thermal trough shifts inland over the weekend and
dissipates for light onshore flow but tranquil conditions for area
waters. Hazardous seas continue over the coastal waters today, but
will fall below 10 feet midweek and remain there into the coming
weekend.

27

&&

.HYDROLOGY...Heavy rain over the south slopes of the Olympics over
the last 24 hours has led to a continue rise on the Skokomish
River in Mason County early this morning. The river is still
expected to rise above flood stage this morning. A Flood Watch
remains in effect for Mason County. Other rivers around the area
rising into Tuesday but snow levels between 2500-3000 feet will
limit the rises and keep the remaining rivers below flood stage.

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...Coastal Flood Advisory until 10 AM PDT this morning for Seattle
     and Vicinity-Tacoma Area.

     Flood Watch through this afternoon for Hood Canal Area-Lower
     Chehalis Valley Area-Olympics.

     Winter Weather Advisory until 5 PM PDT this afternoon for
     Olympics.

     Coastal Flood Advisory until 6 AM PDT early this morning for
     Central Coast-North Coast.

     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 10 AM PDT this morning for East
     Entrance U.S. Waters Strait Of Juan De Fuca-Northern Inland
     Waters Including The San Juan Islands.

     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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