506
FXUS66 KSEW 041717
AFDSEW

Area Forecast Discussion
National Weather Service Seattle WA
917 AM PST Thu Dec 4 2025

.SYNOPSIS...
The transition to active weather is underway as a series of
systems will reintroduce rain and windy conditions today through
the end of the week. A more significant atmospheric river event
is gaining forecast traction early next week for more widespread
rain and potential hydrologic impacts. Coastal flooding due to
higher astronomical tides will remain minor into early next
week.

&&

.SHORT TERM /TODAY THROUGH SATURDAY/...
The upper level ridge that has kept conditions mild is beginning
to flatten, allowing for the first in a series of weather events
to move in this morning for increasingly widespread rainfall.
Expected rainfall through Saturday afternoon will be between 2-4
inches in the Cascades, with isolated peaks to 5 inches. A
quarter to half an inch of rain is expected throughout Puget
Sound. The warm front will keep rain in the forecast today,
with the cold front catching up Friday into the weekend for
additional rain through the weekend. Snow levels will start off
high now through Friday, but lower to around 4000 feet on
Saturday for snow accumulation in the Cascades. Storm total snow
from late Friday night through late Saturday night show around
10-12 inches for Stevens Pass with higher amounts into the North
Cascades and Mount Baker area. Much lighter amounts are
forecast for Snoqualmie Pass on account of the higher snow
levels. Winds will increase Friday afternoon into Saturday with
the cold front passage and be the strongest along the immediate
coast, Strait of Juan de Fuca and portions of the Chehalis
Valley. Expect gusts of 20 to 30 mph through early Saturday
morning.

Highs today will be in the upper 40s, with the high temperatures
climbing back into the 50s as the rain arrives Friday into the
weekend. Lows will be in the 40s.

The Coastal Flood Advisory will remain in effect today as
inundations of around 2 feet above ground level are possible for
the Grays Harbor County coastal areas, including Westport. High
tide will occur around 1130 AM today and 1200 PM on Friday.
Minor coastal flooding may occur on Friday along the northern
coast, but this will be evaluated again in the next forecast
cycle.

&&

.LONG TERM /SATURDAY NIGHT THROUGH WEDNESDAY/...
The long term forecast is certainly where it gets increasingly
interesting. Another weather system will move over a flattened
NE Pacific ridge, bringing about more rain Sunday into Monday.
An additional 1 to 2 inches of rain are likely in the mountains,
with another half to three quarters of an inch in the lowlands.

Both the deterministic and ensemble model solutions are keying
in on a significant atmospheric river event early next week. A
prolonged fetch of exceedingly moist air will take aim at the
PNW on Monday and last into Wednesday. While the track and
duration of the atmospheric river could fluctuate a bit between
now and then, the amount of moisture arriving next week is
enough to signal 5 to possibly 10 inches of rain in the
Cascades, and 2-4 inches in the lowlands. More information can
be found in the hydrology section of this discussion, but will
certainly have the capability to be impactful from a hydrologic
standpoint. Winds will rise as this system moves through the
area, as well as higher snow levels by nature of it being an
atmospheric river. This event will be very closely monitored and
forecast to get a better sense of the range of outcomes and
expected rainfall as it gets closer.

21

&&

.AVIATION...
Northwest flow aloft as a warm front moves through the area. A
mix of MVFR/IFR/LIFR cigs early this morning with rain and
drizzle. MVFR/IFR cigs expected for much of today, continuing
into tonight, as the front stalls over the area. In addition,
substantial low level moisture will result in lowered vsbys,
ranging between 2 to 4 statute miles mainly from 17Z onwards
into this evening. Light winds this morning will increase from
the S/SE this afternoon, mainly between 5 to 10 kts.

KSEA...IFR cig this morning. Ceilings will likely fluctuate
between IFR and low- end MVFR throughout this afternoon. Vsbys
will also lower near 2 to 4 statute miles from 17z through the
afternoon with rain at times. S/SE winds continue through today,
remaining generally around 4 to 6 knots.

JD/Mazurkiewicz

&&

.MARINE...
A warm front will move into the waters today for
increasing south to southeast winds, mainly for the Coastal Waters.
Brief Small Craft Advisory wind gusts are possible for the Coastal
Waters late this morning, but winds are primarily expected to remain
below SCA thresholds. A stronger front will move through late Friday
into Friday night, resulting in increased west winds. Latest
probabilities of gales for the Coastal Waters peak around 50 to 80%
for the outer Coastal Waters, northern inner Coastal Waters, and
western Strait of Juan de Fuca. For this reason, have issued a Gale
Watch Friday afternoon through Friday night. A stronger westerly
push through the Strait of Juan de Fuca is expected late Friday
through Friday night, and another Gale Watch has been issued for the
central and eastern Strait of Juan de Fuca. Onshore flow will
increase elsewhere as well, with additional SCA headlines possible
for other waters beginning Friday afternoon. Additional weather
systems will then move through over the weekend into into next week,
which will result in further increased winds and additional
headlines.

Combined seas will remain 5 to 7 feet through tonight. Seas will
build to 10 feet Friday afternoon, and peak Friday night around 13
to 17 feet. The period will also range 10 to 13 seconds late Friday
into Friday night. Seas will briefly subside below 10 feet on
Sunday, before building above 10 feet later Monday into Tuesday. JD

&&

.HYDROLOGY...
A series of wet weather systems forecast to reach the
area will eventually increase the threat of river flooding this
weekend, especially into the first half of next week. West to
northwesterly flow aloft with the system on Friday will put the area
of greatest precipitation in the North Central Washington Cascades.
Snow levels, at this time, will be rising over 5500 to 6000 feet.

As the flow aloft becomes more westerly to southwesterly the
flood threat will shift to the flood prone Skokomish River late
in the weekend.

There`s still a wide variance in the possible precipitation
amounts with an atmospheric river setting up through the first
part of next week. It is still within the realm of possibility
that we could have a widespread river flooding event on our
hands beginning next Tuesday/Wednesday, with multiple rivers
reaching minor and moderate flood stages. Uncertainty continues to
remain in regards to the exact flood levels and stages through next
week, and as such it will be critical to monitor the forecasts
through the next seven days.

The landslide threat is minimal the next few days. The series
of wet systems will eventually take its toll with the landslide
threat increasing slightly this weekend and rapidly early next
week.

JD/Felton

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...Coastal Flood Advisory until 3 PM PST this afternoon for Grays
     Harbor County Coast.

     Coastal Flood Watch from Friday morning through Friday
     afternoon for Grays Harbor County Coast.

PZ...Gale Watch from Friday afternoon through late Friday night for
     West Entrance U.S. Waters Strait Of Juan De Fuca.

     Gale Watch from Friday afternoon through Saturday morning for
     Central U.S. Waters Strait Of Juan De Fuca-East Entrance
     U.S. Waters Strait Of Juan De Fuca.

     Gale Watch from Friday morning through late Friday night 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 Point Grenville
     To Cape Shoalwater 10 To 60 Nm.

&&

$$