421
FXUS66 KSEW 090933
AFDSEW

Area Forecast Discussion
National Weather Service Seattle WA
133 AM PST Tue Dec 9 2025

.SYNOPSIS...
A strong atmospheric system will continue to bring periods of
heavy rain and gusty winds to western Washington through
Wednesday. Widespread significant river flooding is underway and
is expected to continue through much of the week. Minor coastal
flooding due to astronomical high tides will also pose concerns
for the northern Salish Sea coastlines through much of the week.
Wet and unsettled conditions will continue through the forecast
period.

&&

.SHORT TERM /TONIGHT THROUGH WEDNESDAY NIGHT/...
A strong atmospheric system is well underway across western
Washington this morning, bringing in widespread heavy rainfall
to western Washington alongside breezy winds. The axis of
moisture will continue to shift southward throughout the morning
today behind a cold front with most areas northward of Chehalis
seeing drier conditions, providing a brief lull in rainfall
across the region. However, flooding is still expected despite a
brief decrease in rainfall. Heavy precipitation will fill back
in by this evening as the atmospheric river shifts northward and
takes direct aim once again at western Washington. While this
second wave of precipitation will not bring quite as heavy rain
rates, this longer duration rainfall will keep rivers elevated
across the region, and even potentially causing rivers to peak
higher, with significant river flooding expected to continue
over the next few days.

The following key messages with this atmospheric river system
are outlined below:

* HEAVY RAIN: Despite a decrease in rainfall this morning, the
  atmospheric river system will bring another wave of heavy rain
  to western Washington by this evening, continuing through
  Wednesday night. While areas east of the Olympics will likely
  see some shadowing at the onset of precipitation once again
  this afternoon, heavy rain will continue to cause flooding
  concerns to area rivers, urban areas, and areas with poor
  drainage. Forecast models remain consistent with rainfall
  forecasts, showing an additional 2 to 3 inches of rain across
  the lowlands and 5 to 8 inches over the mountains through late
  Wednesday. Many area rivers have entered major flood stage,
  with another wave of rises expected tonight into Thursday.
  For more details, see the HYDROLOGY section below.

* WINDS: Winds will gradually decrease this morning, with
  another wave of breezy winds this afternoon alongside the
  second wave of rainfall. Wind gusts are expected to reach
  40-45 mph across the region later today as the second wave of
  the atmospheric river system pushes into the region. Winds
  will peak this evening and remain elevated into Wednesday.

* COASTAL FLOODING: Minor coastal flooding remains possible
  today along the northern Salish Sea coastlines 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 this morning, 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 today
which could cause brief slippery travel conditions.

The returning surge of moisture later this afternoon will bring
warmer temperatures and higher snow levels through the remainder
of 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/...
Forecast models remain in good agreement that unsettled
conditions will continue through the remainder of the week and
into early next week as additional systems are set to cross over
the Pacific Northwest. It is likely that impacts from
significant river flooding will linger through Thursday and even
into the weekend for many areas. Mild conditions are favored to
continue through the forecast period, with little relief from
wet conditions in sight for western Washington.

15

&&

.AVIATION...
Generally MVFR to IFR as heavy rainfall from an atmospheric
river slowly shifts southward this morning. This should allow
for some small improvement in ceilings and vis this morning,
though conditions are expected to deteriorate once again as
heavy precipitation fills in across western Washington this
afternoon. North to northeast winds generally 10 to 20 kt with
gusts up to 25 to 30 kt will continue to ease this morning and
shift southerly by 12z. Winds will increase once again this
evening, with speeds returning to 10 to 20 kt with gusts
reaching 30 kt.

KSEA...IFR this morning with slight improvement to MVFR
this morning 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.

29/15

&&

.MARINE...
A strong cold front will move across area waters early this
morning, with strong west winds through the Strait of Juan de
Fuca and coastal waters. Winds will taper off into the late
morning behind the cold front, though seas will remain elevated
between 9 to 14 feet.

The next system arrives late Tuesday night into Thursday,
bringing moderate to heavy rain that may locally reduce
visibilities at times, breezy southwest winds that may reach
gale force, and elevated seas above 10 feet.

Seas will ease into Friday to around 4 to 6 feet, where they
will remain through much of the weekend. Another system will
increase seas and winds early next week.

15

&&

.HYDROLOGY...
A strong atmospheric atmospheric will continue to move through
the Pacific Northwest through Wednesday, bringing significant
heavy rainfall across the area. 72-hour precipitation amounts
between Monday and 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 numerous 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 and 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 this morning to 1 PM PST this
     afternoon 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 this evening for Grays
     Harbor Bar.

     Gale Warning until 4 AM PST early this morning for Admiralty
     Inlet-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-
     Northern Inland Waters Including The San Juan Islands-
     Puget Sound and Hood Canal-West Entrance U.S. Waters
     Strait Of Juan De Fuca.

     Small Craft Advisory until 7 PM PST this evening 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 this morning for Central U.S.
     Waters Strait Of Juan De Fuca-East Entrance U.S. Waters
     Strait Of Juan De Fuca.

&&

$$