716
FXUS66 KSEW 090615
AFDSEW

Area Forecast Discussion
National Weather Service Seattle WA
1015 PM PST Mon Dec 8 2025

.SYNOPSIS...
A strong atmospheric river has moved into the region, and will
bring periods of moderate to heavy rainfall and gusty winds to
western Washington through Wednesday. There remains high risk
of widespread and significant river flooding across the region
through much of the week. Minor coastal flooding due to high
astronomical high tides will also remain possible for the Salish
Sea coastlines through the first part of the week. Wet and
unsettled conditions will continue through the end of the week.

&&

.SHORT TERM /TONIGHT THROUGH WEDNESDAY NIGHT/...

Precipitation associated with a strong atmospheric river has
moved into the Pacific Northwest this afternoon, and is expected
to affect the region directly through Wednesday, and indirectly
through the remainder of the week. The key messages regarding
this system are highlighted below:

* HEAVY RAIN: Extended periods of moderate to heavy rain to
  western Washington through Wednesday. Latest forecast models
  have remained fairly consistent, with the heaviest rainfall
  arriving today. The moisture plume still looks to briefly
  shift southward early Tuesday, easing accumulations for some
  areas before lifting back northward late Tuesday through
  Wednesday. While areas east of the Olympics will likely see
  some shadowing at the onset of precipitation, conditions
  across all of western Washington will be very wet through
  Wednesday. Areas generally south of Seattle will see 3 to 6
  inches of rainfall through Thursday morning in a 72 hour
  period, with the Olympics and Cascades on track to see 8 to 12
  inches of rain in this timeframe. Locally higher amounts are
  possible over the southern and central Cascades, where amounts
  could reach 15 inches or more in 72 hours. This is expected
  to bring significant river flooding to western Washington,
  with many area rivers forecast to reach moderate or major
  flood stage by mid-week. A Flood Watch remains in effect for
  all of western Washington through Friday morning. For more
  details, see the HYDROLOGY section below.

* WIND: Conditions will be windy area-wide today, with
  southwesterly winds picking up throughout the day. Winds will
  peak late in the afternoon and evening, with the strongest
  gusts along the Pacific Coast reaching 50-55 mph. Gusts
  elsewhere across the interior will reach 40-45 mph at times.
  Winds will gradually ease into Tuesday, but conditions will
  remain breezy at times.

* COASTAL FLOODING: Minor coastal flooding remains possible
  along the Salish Sea coastlines through the first half of the
  week with high astronomical tides. While the tides will
  generally remain below or nearing thresholds, heightened river
  flows or wind effects could exacerbate inundation in some
  areas around high tide.

In addition, snow levels will briefly lower to near 3500-4000
feet over the mountains early Tuesday, resulting in
minor accumulating snow generally above 4500 feet. The higher
mountain passes, including Stevens Pass and White Pass, will
likely see a few inches of snow accumulation throughout the day
Tuesday which could cause brief slippery travel conditions.

The returning surge of moisture later Tuesday afternoon will
bring warmer temperatures and higher snow levels through the
week. Temperatures will peak well above normal most days this
week, with temperatures in the low to upper 50s across the
lowlands.

&&

.LONG TERM /THURSDAY THROUGH MONDAY/...
Unsettled conditions continue to be expected into the weekend,
though precipitation amounts will start to taper across western
Washington by Thursday. It is likely that impacts like lingering
river flooding and elevated landslide risk will linger through
Thursday for many areas. Ensembles a system likely to brush the
area Thursday, with extended long range ensembles hinting at a
break Friday, followed by another stronger system likely
focused to the north over British Columbia early Saturday and
then possibly Western Washington Saturday into Sunday.

15

&&

.AVIATION...
Majority of the terminals IFR this evening as a weather system
continues to push through the region. Precipitation is slowly
pushing southward away from the terminals and may lead to some high-
end MVFR or low-VFR improvement. Already seeing northerly flow at
PAE and expecting BFI and SEA to shift NE shortly after 06Z.
Expecting winds to shift southerly again after 12Z. Winds will
gradually subside overnight to around 5-10 kt, but are expected to
increase again Tuesday evening, with sustained speeds 10-15 kt and
gusting to 20-30 kt.

KSEA...Currently IFR at the terminal and conditions should improve
slightly to MVFR overnight after 12Z. May see some brief improvement
to low-end VFR conditions around 21Z, but ceilings are expected to
deteriorate late Tuesday evening into the overnight hours to IFR.
Southerly flow at the terminal is expected to switch NE around 06Z
tonight, gusting to 25-30 kt. SW winds return after 12Z and winds
will gradually subside late Tuesday morning to 5-10 kt. Winds will
increase again late Tuesday evening to 10-15 kt, gusting to 20-30
kt.

29

&&

.MARINE...
The first frontal system from an atmospheric river continues to
impact area waters today. The areas with the breeziest SW winds this
afternoon are the coastal waters and the interior waters. As the
cold front kicks in, strong west winds will pick up in the Strait of
Juan de Fuca through tonight. The wind threat will end early Tuesday
morning across all waters as winds decrease behind the cold front.
Hazards were adjusted to account for the extended duration of winds
behind the front, and also seas of 10-15 ft dropping to 9-12 ft
Tuesday. Heavy rain will continue tonight into Tuesday morning,
which may reduce visibilities at times. The next system arrives late
Tuesday night through Thursday, with more moderate to heavy rain,
breezy winds southwest winds (most likely remaining below gale force
at this time, but most hazardous to small craft), and seas remaining
above 10 ft through Thursday at 9-11 ft, decreasing to 4-6 ft Friday
through Saturday. Another system will increase seas and winds early
next week.

HPR

&&

.HYDROLOGY...
A strong atmospheric atmospheric will move through the Pacific
Northwest through Wednesday, bringing significant heavy rainfall
across the area. 72-hour precipitation amounts between ending
Thursday morning will likely reach 2 to 6 inches across the
lowlands, with 6 to 10 inches over the Olympics and Cascades
with locally higher amounts up to 12 inches over the central and
southern Cascades.

Rivers continue to rise across the region, with many flood
warnings in effect. Consult weather.gov/seattle for the latest.
While some uncertainty does still remain in regards to the exact
flood levels and stages through the next week, many river
forecast points are projected to reach major flood stage in the
days ahead. Therefore, it will be critical to monitor the
forecasts now and through the next seven days. Additional
precipitation is also possible Thursday into Friday, which may
keep rivers elevated heading into the weekend. A Flood Watch
remains in effect across all of western Washington through
Friday.

With the wet antecedent soil conditions, the landslide threat
across the region will increase with this system. Potential has
also increased for debris flows over area burn scars, which will
continue to be monitored.

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


&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...Flood Watch 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 from 7 AM to 1 PM PST Tuesday for
     Lowlands of Western Skagit and Northwestern Snohomish
     Counties-Lowlands of Western Whatcom County-San Juan
     County.

PZ...Small Craft Advisory until 7 PM PST Tuesday for Grays Harbor
     Bar.

     Gale Warning until 1 AM PST Tuesday 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 from 1 AM to 7 PM PST Tuesday 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.

     Gale Warning until 7 AM PST Tuesday for Central U.S. Waters
     Strait Of Juan De Fuca-East Entrance U.S. Waters Strait
     Of Juan De Fuca.

     Gale Warning until 4 AM PST Tuesday for Admiralty Inlet-
     Northern Inland Waters Including The San Juan Islands.

     Gale Warning until 2 AM PST Tuesday for Puget Sound and Hood
     Canal.

&&

$$