385
FXUS66 KSEW 100029
AFDSEW
Area Forecast Discussion
National Weather Service Seattle WA
429 PM 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 has been 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
the remainder of the week.
&&
..SHORT TERM /TONIGHT THROUGH WEDNESDAY NIGHT/...
A strong atmospheric system is well underway across the Pacific
Northwest. The axis of moisture has shifted to the south this
afternoon with most areas northward of Chehalis seeing drier
conditions, which has provided 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
later this afternoon into the early hours of the evening as the
atmospheric river shifts northward and takes direct aim once
again at western Washington.
This second wave of precipitation will have a longer duration
of rain, with latest guidance trending a little bit wetter than
previous forecasts. This longer duration rainfall will keep
rivers elevated, with another round of rises on area rivers -
potentially even peaking higher than the previous round.
Significant river flooding is expected to continue over the next
several days. The following key messages with this atmospheric
river system are outlined below:
* HEAVY RAIN: Despite a decrease in rainfall this afternoon,
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: Another wave of breezy winds can be expected alongside
the second wave of rainfall. Wind gusts are expected to reach
40-45 mph across the region late this evening as the second
wave of the atmospheric river system pushes into the region.
Winds will remain breezy through Wednesday.
* COASTAL FLOODING: Minor coastal flooding remains possible
along the northern Salish Sea coastlines during Wednesdays
high astronomical tide. 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 are generally near 3500-4000 feet over
the mountains, which has resulted in minor accumulating snow
this afternoon generally above 4500 feet. Snow levels will begin
to rise rapidly by this evening to 7000 to 9000 feet as the
atmospheric river shifts northward.
The returning surge of moisture later this evening will bring
warmer temperatures and higher snow levels throughout 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. Latest ensemble data have
shown potentially more systems on the way through the early part
of next week, starting on Monday, which will keep the pattern
wet and active.
15/Mazurkiewicz
&&
AVIATION...
This afternoon: a break continues across western WA in between
atmospheric river systems. Ceilings are a mix between MVFR and VFR
with BKN to OVC decks overhead, with light south winds 5-10 kt. The
next frontal system associated with the atmospheric river will
approach with a warm front to the southwest late tonight, and a cold
front will follow very quickly behind into Wednesday/Thursday. Rain
will arrive in the southern terminals as early as 00Z, and spread
northward through the evening into Wednesday and Thursday. Some of
the bands of rain may produce moderate to heavy precipitation rates,
reducing visibilities down to 2 SM. Ceilings will gradually lower to
MVFR tonight, and eventually IFR/LIFR Wednesday morning (best chance
of LIFR is along the coast). Mist will likely accompany the lower
ceilings, with visibilities down to 2-4 SM. The lower conditions are
expected to persist through Wednesday and up to at least early
Thursday. Breezy southwest winds 15-20 kt gusting to 30-35 kt are
expected most of Wednesday, with the strongest winds along the coast
and central/south interior terminals.
KSEA...VFR through early this evening. Rain showers will begin
arriving as early as 00-02Z, and become steady tonight into
Wednesday. Moderate to heavy rain may reduce visibilities down to 2
SM at times. South winds 5-10 kt will increase late tonight to 15-20
kt gusting to 35 kt through most of Wednesday, decreasing to 5-10 kt
late Wednesday evening. Ceilings to lower to MVFR as rain arrives
this evening, with IFR likely Wednesday morning through evening.
HPR
&&
.MARINE...
The second frontal system with an atmospheric river will arrive
later this evening and persist into Wednesday. Moderate to heavy
rain over the waters (along with lower ceilings and mist) may reduce
visibilities at times. South winds will begin to increase tonight,
and persist into much of Wednesday. West winds will follow in the
Strait of Juan de Fuca late Wednesday evening. Most waters are under
small craft advisories for the breezy winds. The inner coastal
waters and west/central Strait of Juan de Fuca were upgraded to gale
warnings with frequent gusts to 35 kt likely this evening. Puget
Sound waters is the next area being monitored for a possible upgrade
to a gale warning (but confidence was not high enough to issue it
this afternoon). Winds will decrease below any concern Thursday
through early next week, where another system may produce gusty
small craft winds for the coastal waters, and interior waters.
Seas of 8-12 ft will continue through Thursday, decreasing to 6 to 8
ft Sunday, increasing to 10-13 ft early next week.
HPR
&&
.HYDROLOGY...
A strong atmospheric atmospheric will continue to
move through the Pacific Northwest through Wednesday, shifting
back north, and bringing significant heavy rainfall across the
area. 48-hour precipitation amounts ending Wednesday night will
likely reach 2 to 4 inches across the lowlands, with 6 to 10
inches over the Olympics and Cascades with locally higher
amounts over 12 inches in the the central and southern
Cascades.
Most rivers across western Washington will be affected by this
second wave and flood warnings remain in effect. Consult
weather.gov/seattle for the latest. While some uncertainty does
still remain in regards to the exact flood levels and stages, 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 to 1 PM PST Wednesday for
Lowlands of Western Skagit and Northwestern Snohomish
Counties-Lowlands of Western Whatcom County-San Juan
County.
Wind Advisory from 8 PM this evening to 10 PM PST Wednesday
for City of Seattle-Downtown Everett / Marysville Area-
Eastern Kitsap County-Eastside-Foothills of the Western
and Southern Olympic Peninsula-Grays Harbor County Coast-
Lower Chehalis River Valley-Lowlands of Lewis and
Southern Thurston Counties-Lowlands of Pierce and
Southern King Counties-Middle Chehalis River Valley-
Northern Washington Coast-Olympia and Southern Puget
Sound-Shoreline / Lynnwood / South Everett Area-Southern
Hood Canal-Willapa and Black Hills.
PZ...Small Craft Advisory until 10 PM PST Wednesday 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-Grays Harbor Bar.
Gale Warning from 8 PM this evening to 10 PM PST Wednesday for
Central U.S. Waters Strait Of Juan De Fuca-West Entrance
U.S. Waters Strait Of Juan De Fuca.
Small Craft Advisory from 8 PM this evening to 10 PM PST
Wednesday for Admiralty Inlet-East Entrance U.S. Waters
Strait Of Juan De Fuca-Northern Inland Waters Including
The San Juan Islands-Puget Sound and Hood Canal.
Gale Warning until 10 PM PST Wednesday 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.
&&
$$
NWS SEW Office Area Forecast Discussion