522
FXUS66 KSEW 062223
AFDSEW

Area Forecast Discussion
National Weather Service Seattle WA
223 PM PST Sat Dec 6 2025

.SYNOPSIS...
Active weather continues, with a certain increase in activity as
a strong atmospheric river arrives early next week. Heavy rain,
river flooding, wind and high elevation snow are in the forecast
for the foreseeable future. Coastal flooding due to high
astronomical tides will remain minor into the first part of the
week.

&&

.DISCUSSION...

KEY MESSAGES:

* RAIN: Following a weaker system moving through the area
  Sunday, a strong atmospheric river will bring several rounds
  of heavy precipitation to the area Monday and into Wednesday.
  The biggest change in the forecast is the main axis of
  moisture has shifted farther south into Southwest Washington,
  and overall QPF amounts through the 72-hour period have come
  down slightly. This has lowered the river forecasts a touch
  compared to yesterday, but the key message of widespread
  flooding has not changed. More details are below in HYDROLOGY.

* WIND: Breezy conditions are expected throughout the week, but
  the strongest winds are expected on Monday, on the onset of
  the atmospheric river event. Wind gusts of up to 30-45 mph are
  in the forecast across the area, though the strongest winds
  are expected along the coast, in southwest Washington, and
  through the Cascades.

* COASTAL FLOODING: Minor coastal flooding is expected through
  portions of the interior waters, mostly to the north. Compound
  flooding from high river flows by mid-next week may prolong or
  exacerbate the threat of coastal flooding.

Continued moist, onshore flow is maintaining scattered showers
across much of the region, except the central Puget Sound area
where the showers are getting shadowed. Snow levels continue to
remain just above pass level, allowing for rain at Snoqualmie
Pass and a rain/snow mix at the higher passes where temperatures
sit just a degree or two above freezing. Showers should taper
off this evening for a bit of break until the next system
arrives across the area early Sunday. The precipitation falling
on Sunday will be generally not impactful; amounts of up to a
quarter to a half of inch of rain through the interior, with up
to an inch or two in the mountains. These rains however, will
allow rivers to rise up a bit once again, and prime the soils
for what will arrive next week. Showers again may taper off
Sunday night but there will not be much of a break in the
precipitation.

The first push from the atmospheric river arrives to the area
early Monday. Rain will continue through much of the day before
beginning to sink southward Monday night. By Tuesday, most of
the rain will be focused south of the area, which may allow the
northern half of the state to see a brief break in at least the
heaviest rain rates. However, another big push of precipitation
will move in late Tuesday into Wednesday. This is the portion of
the system that has shifted a bit farther south. Models have
also begun to come more into consensus that another (albeit
less impactful) system is forecast to arrive Thursday night into
Friday. What happens with this system (will it be more
progressive or will it stall out again over the area?) is still
unclear with more significant differences in the forecast
Friday and beyond.

In the main atmospheric river (72 hours from Monday -
Wednesday), amounts remain track with around 2-4" of rain
through the lowlands and along the coast, as well as 4 to 8 to
locally 10+" of rain over the mountains, with the heaviest
precipitation amounts across the southern half of the CWA. The
key message has not changed: widespread river flooding, as well
as urban and small stream flooding, remains a significant risk
across the entire area. See more below.

Temperatures will remain above average through the week, with
highs in the low to mid 50s and lows in the 40s.

62

&&

.AVIATION...
A weak trough and trailing frontal system will push through western
WA today into Sunday with showers at times across the terminals.
Expect an increase in coverage of the showers Sunday morning, with
visibility reductions at times. MVFR BKN ceilings continue to linger
this afternoon in portions of the interior and coast, with VFR
elsewhere. Ceilings are expected to lower tonight into Sunday.
Probabilistic guidance heavily favors MVFR ceilings regionwide (with
LIFR in the mountains), though there is a low chance for a couple
IFR ceilings (with mist) at times in a few of the southern interior
terminals. Winds will continue to decrease at the surface through
tonight, but a few gusts exceeding 20 kt will linger in Puget
Sound/south interior areas through as late as 03-06Z. Flow aloft
remains west/northwest, although light enough just above the surface
to where wind shear is not expected to be a significant concern.
Winds pick up again late Sunday morning through the afternoon with
gusts 20-25 kt possible out of the southwest.

KSEA...Mixed VFR/MVFR ceilings continue this afternoon, which will
improve to VFR later into the evening. Brief shower to the west will
be within the vicinity 22-00Z this afternoon (expect brief lower
ceilings and visibilities with it). Models heavily favor MVFR
ceilings going into tonight/all of Sunday (as soon as 12Z) with
ceilings dropping to as low as 1,000-1,500 ft. There remains a 10%
chance of IFR (which would be towards the Puget Sound waters if it
were to drop below 1,000 ft). Shower chances decrease through the
evening, and increase again early Sunday morning. Breezy southwest
winds 10-15 kt with gusts to 20 kt will decrease to 5-10 kt tonight,
then increase back to 8-12 kt with gusts to 20-25 kt late Sunday
morning through early Monday morning.

HPR

&&

.MARINE...
Onshore flow will continue to ease across the area waters tonight
and waves currently between 12-15 ft will subside for a brief
break in between weather systems. Another frontal system will
move across the area waters on Sunday, bringing another round of
increasing southerly winds to the waters. At this time, winds
generally look to remain between 20-30 kt for most of the
coastal and interior waters. Winds will peak during the afternoon
hours again before subsiding. A stronger weather system will
then move into the waters Monday, likely bringing gales to
portions of the area waters. Additional weather systems will
move across the area mid to late next week.

Seas over the coastal waters will slowly subside to 9 to 11
feet by late tonight. Though, expect seas to build back towards
14-16 ft on Monday and remain elevated into midweek.

14

&&

.HYDROLOGY...
A series of wet weather systems moving across the region will
increase the threat of river flooding early next week. While
there`s still some uncertainty in the precipitation amounts
with an atmospheric river moving into the region, confidence
continues to increase that a widespread river flooding event
will commence late Monday and continue through much of the week.
Multiple rivers flowing off the Cascades and the Olympics are
forecast to reach Minor, Moderate, and Major flood stage. While
uncertainty does remain in regards to the exact flood levels
and stages through the next week, it will be critical to monitor
the forecasts through the next seven days. Additional precipitation
is also possible Thursday into Friday, which will keep rivers
elevated through the second half of the week.

The series of wet systems will also start to elevate the landslide
risk across the region. As soils become more saturated next week,
there will be an increased potential for landslides and debris
flows on burn scars.

Urban and small stream flooding, as well as areas with poor
drainage, should be alert to the potential for localized
nuisance flooding. Low water crossings may become impacted or
impassable.

14/62

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...Coastal Flood Advisory from 5 AM to 11 AM PST Sunday for
     Lowlands of Western Skagit and Northwestern Snohomish
     Counties-Lowlands of Western Whatcom County-San Juan
     County.

     Flood Watch from late Sunday night through Friday afternoon
     for Cascades of Pierce and Lewis Counties-Cascades of
     Snohomish and Northern King Counties-Cascades of Southern
     King County-Cascades of Whatcom and Skagit Counties-City
     of Seattle-Downtown Everett / Marysville Area-Eastern
     Kitsap County-Eastern Strait of Juan de Fuca-Eastside-
     Foothills and Valleys of Central King County-Foothills
     and Valleys of Pierce and Southern King Counties-
     Foothills and Valleys of Snohomish and Northern King
     Counties-Foothills and Valleys of Thurston and Lewis
     Counties-Foothills and Valleys of the North Cascades-
     Foothills of the Western and Southern Olympic Peninsula-
     Grays Harbor County Coast-Island County-Lake Crescent
     Area Including US 101-Lower Chehalis River Valley-
     Lowlands of Lewis and Southern Thurston Counties-Lowlands
     of Pierce and Southern King Counties-Lowlands of Western
     Skagit and Northwestern Snohomish Counties-Lowlands of
     Western Whatcom County-Middle Chehalis River Valley-
     Northern Hood Canal-Northern Washington Coast-Olympia and
     Southern Puget Sound-Olympics-Port Townsend Area-San Juan
     County-Shoreline / Lynnwood / South Everett Area-Southern
     Hood Canal-Western Strait of Juan de Fuca-Willapa and
     Black Hills.

     Coastal Flood Advisory until 3 PM PST this afternoon for Grays
     Harbor County Coast.

PZ...Small Craft Advisory until 10 PM PST this evening for Grays
     Harbor Bar.

     Small Craft Advisory until 1 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-West Entrance U.S.
     Waters Strait Of Juan De Fuca.

     Small Craft Advisory until 7 PM PST this evening for Central
     U.S. Waters Strait Of Juan De Fuca-East Entrance U.S.
     Waters Strait Of Juan De Fuca-Northern Inland Waters
     Including The San Juan Islands.

     Small Craft Advisory until 4 PM PST this afternoon for Puget
     Sound and Hood Canal.

&&

$$