Area Forecast Discussion
Issued by NWS Seattle/Tacoma, WA

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FXUS66 KSEW 251652
AFDSEW

Area Forecast Discussion
National Weather Service Seattle WA
852 AM PST Sun Feb 25 2024

.SYNOPSIS...The first of several weather systems arrives today
with heavy mountain snow, lowland rain, and locally windy
conditions developing. Snow levels will drop below 1000 feet
behind the front Sunday night into Monday. Another strong front
arrives on Wednesday with cool and unsettled conditions to follow
through the end of the coming week.

&&

.SHORT TERM /TODAY THROUGH TUESDAY/...Approaching cold front is
moving through central Vancouver Island as of 1645Z and will sweep
southeastward through Puget Sound around 22Z this afternoon.
Olympics have formed an effective rain shadow for much of central
Puget Sound thus far, but we should see the shadow shrink somewhat
as front approaches. Precip rates are picking up in the Cascades and
the snow will really begin to pile up there as the day wears on and
orographic lift increases. Forecast looks on track and see no
necessary updates this morning. Previous discussion follows with
updates to marine and aviation portions.   27

An active weather pattern brings heavy mountain snow, gusty winds
and a threat of lowland snow to western WA over the short term.

Strong, moist, westerly flow prevails over the Pac NW with the
polar jet dipping south. Initially, snow levels in the mountains
will hover around 4000 ft but snow levels will drop further as
the day progresses and fall below all pass levels this evening.
In general, we`re looking at storm total snowfall amounts between
1 to 3 feet in the Cascades and the Winter Storm Warning remains
in effect.

Down in the lowlands, showers expected today although the central
sound (and Seattle) may see some rain shadowing with westerly
downslope winds off the Olympics. A strong post-frontal onshore
push is expected through the Strait of Juan de Fuca this afternoon
and evening with westerly wind gusts of 30-40 mph across the east
strait, Admiralty Inlet area down to Everett. Winds will ease
late this evening.

The air mass will cool significantly overnight as a trough drops
down from B.C. Snow levels will lower to around 500 ft and there`s
a threat of a rain/snow mix across much of the lowlands into
Monday morning. However, with the flow remaining onshore, surface
temperatures will remain above freezing which will help limit
accumulations and overall impacts. One area of concern would be
the East Puget Sound Lowlands near the Cascades (like North Bend)
where minor accumulations are possible, especially with heavier
showers. In addition, thunderstorms are possible along the coast
where instability is the greatest.

The air mass remains cool on Tuesday under northerly flow.
Showers, for the most part, are limited to the coast and
mountains. The flow briefly turns offshore and with some clearing
we may see morning temperatures near freezing. With this in mind,
there`s another threat of lowland rain/snow mix although
accumulations (if any) remain low. 33

.LONG TERM /WEDNESDAY THROUGH SATURDAY/...Another wet/active
period of weather is slated for Tuesday night and Wednesday as the
next strong Pacific storm system moves in. More heavy snow is
forecast in the Cascades with possible travel impacts over the
highway passes. With the flow turning back to onshore, the overall
lowland snow threat will diminish.

The pattern is a little quieter past midweek as an upper low
spins overhead and the jet shifts south over CA. Although, we`ll
still see a few lingering showers and temperatures will track
below normal. Snow levels dip again Thursday night into Friday and
again Friday night into Saturday for yet another rain/snow mix
threat in the lowlands. However, at this point, widespread and/or
significant accumulations are not expected. 33

&&

.AVIATION...Northwesterly flow aloft turning gradually to the west
this evening and tonight as an upper level trough deepens over the
region. A passing front will result in surface winds increasing
throughout W WA today, reaching their peak speeds this afternoon and
evening before slowly tapering off. Most terminals will see
southerly sustained winds ranging 10-15 kts with gusts up to 30 kts,
however terminals prone to higher wind speeds such as HQM or
orographic enhancement such as CLM could see faster sustained speeds
of 15-20 kts with gusts up to 40 kts.

CIGs generally IFR this morning, as precipitation fills in coverage.
Robust down-sloping/Foehn winds ongoing off the Olympics and
Cascades with significant rain shadowing across the central Puget
Sound terminals. CIGs should slowly lift as they trend towards MVFR
thresholds this morning as mixing increases and winds continue to
strengthen into the afternoon.

KSEA...IFR CIGs continue this morning, though approaching MVFR once
again as winds continue to strengthen and enhance mixing. Mostly
mist and drizzle through 00Z with considerable rain shadowing
continuing off the Olympics, though cannot rule out periods of light
rain overcoming this from time to time. Better chances for rain will
be closer to 00-06Z as a convergence band shifts southward, though
disagreement in how far south the band and wind shift to the north
reaches with consensus being closer to BFI than SEA. Otherwise,
south-southwesterly winds from 15 to 20 kt with gusts increasing to
25 to 30 kt by 20Z, then gradually easing through the overnight as a
cold front pushes further south and east of the area.

Davis/18

&&

.MARINE...Strong onshore flow via a cold front passing through the
area will bring strong winds across all waters throughout the day
Sunday and spilling over into Monday. Small Craft Advisories and
Gale Warnings continue as southwesterly winds continue to gust this
morning with a shift westward and a significant push down the Strait
of Juan de Fuca in association with the passage of a cold front.
Gale Warnings continue for the offshore waters early Monday morning
with the greatest confidence for gales is over the far western
bounds of the offshore zones (40-50%).

Seas around 8-12 feet before increasing to 12-16 feet tonight. Seas
will gradually lower by Tuesday, hovering around 10 feet through the
middle of the week. Seas look to increase back to near 12-16 feet
Thursday into Friday as low pressure settles over the region for
much of the second half of the week.

Davis/18

&&

.HYDROLOGY...No river flooding is in the forecast over the next 7
days, but moderate to heavy precipitation will enter the region into
next week. This precipitation may contribute to river rises across
western Washington with the Skokomish River being the most
sensitive.

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...Winter Storm Warning until 4 PM PST Monday for West Slopes North
     Cascades and Passes-West Slopes North Central Cascades and
     Passes.

     Winter Storm Warning from 10 AM this morning to 4 PM PST Monday
     for West Slopes South Central Cascades and Passes.

PZ...Small Craft Advisory until 10 AM PST this morning for Central
     U.S. Waters Strait Of Juan De Fuca-East Entrance U.S.
     Waters Strait Of Juan De Fuca-West Entrance U.S. Waters
     Strait Of Juan De Fuca.

     Gale Warning from 10 AM this morning to 10 PM PST this evening
     for Central U.S. Waters Strait Of Juan De Fuca-East
     Entrance U.S. Waters Strait Of Juan De Fuca-West Entrance
     U.S. Waters Strait Of Juan De Fuca.

     Small Craft Advisory until 4 AM PST Monday for Northern Inland
     Waters Including The San Juan Islands-Puget Sound and Hood
     Canal.

     Small Craft Advisory from 10 AM this morning to 4 AM PST Monday
     for Admiralty Inlet.

     Small Craft Advisory until 4 PM PST Monday for Coastal Waters
     From Cape Flattery To James Island Out 10 Nm-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 midnight PST tonight 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.

     Gale Warning from midnight tonight to 4 AM PST Tuesday 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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