Washington State Forecast Discussion

Western Washington


272
FXUS66 KSEW 282323 AAA
AFDSEW

Area Forecast Discussion...UPDATED
National Weather Service Seattle WA
323 PM PST Sat Dec 28 2024

.SYNOPSIS...An active weather pattern will continue across western
Washington over the weekend as a series of weather systems moves
across the area. A brief break in the pattern will be possible
late Monday into Tuesday, before additional systems move into the
region mid to late week.


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.SHORT TERM /TONIGHT THROUGH TUESDAY/...Scattered showers persist
across western Washington this afternoon associated with onshore
flow behind a front that moved through the area early this
morning. Winds are breezy this afternoon with gusts as high as 30
to 40 mph bring reported across the area. Showers and winds
should taper off this evening into tonight, but the break will be
short lived as a front approaches from the south tomorrow morning.
Satellite imagery this afternoon is already showing high clouds
moving in, well ahead of the front. This system Sunday should be
fairly fast moving as the weak low pressure center offshore
swiftly moves northward into Sunday afternoon and evening. Overall
expecting mostly light rain over the area, up to half an inch of
liquid precipitation over the Olympic Peninsula and interior
lowlands, with higher amounts up to around 1 inch of liquid-
equivalent precipitation over the central and southern Cascades.
There is a very slight chance

Snow levels will slowly lower tonight into tomorrow to and below
pass level (as low as 2500 ft by early Monday morning), allowing
for another round of accumulating snow at the passes. Highest
accumulations will be through the southernmost portions of the
area, including White Pass, with amounts decreasing moving north.
There is potential for heavy snow rates, potentially as high as
0.75 to 1 in per hour Sunday afternoon into early Sunday evening
with the potential for some orographic enhancement and low-level
convergence over east-central King County into southeast Snohomish
County. It is difficult to pinpoint exactly where this
precipitation bullseye will set up exactly, but the highest
amounts are expected to remain over the highest peaks with some
slight precipitation enhancement directly over the passes.
Luckily, the biggest limiting factors to significant accumulation
will be the speed of the system as well as its warmth, with snow-
to-liquid ratios forecast to be around as low as 8:1 Sunday
afternoon, increasing to 11:1 by early Monday morning. Total snow
accumulations going into Monday morning look to hover in the 8 to
11 in for Stevens and Snoqualmie Passes, with slightly higher
amounts at White Pass. With the bulk of the moisture to the south,
only light accumulations are expected through the Olympics and
the North Cascades.

Precipitation chances will taper off Monday and into early
Tuesday as a weak surface ridge builds temporarily. This ridge
will allow for a colder night Monday night, with Tuesday morning
lows in the low to mid 30s, with below freezing possible through
the Cascade foothills. This rain break will be short-lived
however, with the next frontal system is on its heels, approaching
the coast by Tuesday evening.

Turning towards coastal hazards, wave heights are peaking this
afternoon around 20 ft, but should steadily decrease this evening,
with high surf conditions ending tonight. Lastly, the potential
for minor coastal flooding, particularly along the Strait of Juan
de Fuca and the northern interior waters will need to be monitored
this weekend into early next week with perigean spring tides as
the new moon occurs on Monday.

.LONG TERM /WEDNESDAY THROUGH SATURDAY/...Another frontal system
will work through the area Wednesday, with the pattern remaining
active with additional systems late week into next weekend. These
systems look warmer with snow levels rising to 4000-6000 ft by the
end of the week. Additional periods of rain, high-elevation snow,
and breezy winds will remain in the long term forecast, though
nothing stands out as particularly impactful at this point. Will
continue to monitor as details become clearer.

62

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.AVIATION...Rain showers have decreased with a mix of MVFR and VFR
conditions across the region. We'll continue to see some gusty
southerly winds through the Puget Sound terminals to 25-30 kt
through the early evening, but these should decrease as the winds
eventually ease and back to be from the southeast or south
overnight. The next front begins to lift north toward the region
overnight, with a return of lower ceilings and rain showers early
Sunday morning.

KSEA...Gusty southerly winds to 30 kt continue this afternoon but
will ease later this evening. Shower coverage continues to decrease
with lingering MVFR ceilings but some patches of clearing sky
evident around the larger terminal area. Expect decreasing winds
after 00z, with winds becoming southeast or east after 07z tonight.
Ceilings again lowering Sunday morning as additional showers move
through ahead of the next frontal system. Meanwhile, expect winds to
become northerly after 12-14z Sunday and become a bit stronger with
winds around 10 kt and possibly gusting to 15-17 kt. Winds return
to southerly later in the day Sunday.

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.MARINE...Winds continue to ease this afternoon in between weather
systems. Meanwhile, seas continue to run around 17 to 20 ft over
most of the coastal waters (slightly lower in the far north), so the
small craft advisory remains in effect until Sunday for the coastal
zones and the western Strait of Juan de Fuca. The next frontal
system will lift north and bring some winds into the 15-20 kt range,
and while widespread advisory winds aren't expected over the coastal
waters, the advisory for seas will remain. After a bit of a lull
early in the week, the next front will reach the waters later
Tuesday into Wednesday and bring a better chance at more substantial
advisory winds to the coastal waters and the eastern Strait of Juan
de Fuca.

Cullen

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.HYDROLOGY...Several rounds of rainfall are expected over the next
week as a series of systems track across western Washington.
Currently, the Skokomish is the only river in flood and forecast
to remain in flood stage over the next few days. The Chehalis
River has crested downstream at Grand Mound, and the forecast
keeps the river at action stage at Porter. A break
in the rain will allow for rivers to recede later Monday into
Tuesday before an active, wetter period begins again mid to late
week. Several inches of rain will be possible over the Olympic
Peninsula through late next week, bringing the potential for
additional rises on Olympic area rivers.

14/62

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.SEW WATCHES/WARNINGS/ADVISORIES...
WA...High Surf Advisory until 7 PM PST this evening for Central Coast-
North Coast.

Winter Weather Advisory from 7 AM Sunday to 10 AM PST Monday for
West Slopes North Central Cascades and Passes.

Winter Storm Warning from 1 AM Sunday to 4 AM PST Monday for
West Slopes South Central Cascades and Passes.

PZ...Small Craft Advisory until noon PST Sunday for Grays Harbor Bar.

Small Craft Advisory until 4 AM PST Sunday for West Entrance
U.S. Waters Strait Of Juan De Fuca.

Small Craft Advisory until 4 PM PST this afternoon for Central
U.S. Waters Strait Of Juan De Fuca-Puget Sound and Hood
Canal.

Small Craft Advisory until 6 PM PST 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.

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