399
FXUS66 KSEW 031740
AFDSEW

Area Forecast Discussion
National Weather Service Seattle WA
940 AM PST Wed Dec 3 2025

.SYNOPSIS...
Warm front moving over upper level ridge offshore brushing the
northwest corner of the area later today. Trailing cold front
arriving Thursday. Offshore ridge weakening Thursday night into
Friday. A series of stronger and wetter weather systems will
move through Western Washington beginning Friday with an
atmospheric river event likely next Monday and Tuesday.

&&

.SHORT TERM /TODAY THROUGH FRIDAY/...
Cloudy and drizzly conditions across the northwestern portion
of the area will continue through much of today. The forecast
remains on track with an updated aviation section below. 62

Upper level ridge remaining in place offshore today. Warm front
riding over the top of the ridge will brush the northwest
corner later this morning into this afternoon. Ridge axis too
far offshore to provide enough subsidence to get rid of the low
level moisture. Light flow in the lower levels plus middle and
high level clouds moving overhead later today will also
contribute to the low level moisture remaining intact. Under
cloudy skies there will be little in the way of daytime heating
with highs only a few degrees warmer than the current
temperatures, mostly in the mid 40s.

Trailing cold front moving down the British Columbia coast
tonight with the front over the northern top of Vancouver Island
by 12z Thursday. Cloudy skies continuing with rain over the
northern portion of the area after midnight and a chance of rain
over the southern sections. Lows a couple of degrees either
side of 40.

Front moving into Western Washington Thursday making for a
rainy day. Surface low associated with the front fairly weak so
not forecasting any impactful winds. Highs in the mid 40s to
lower 50s.

Front dropping south into Western Oregon Thursday night. Rain
with the front coming to an end by midnight but with the
saturated lower levels some very light rain/drizzle could
continue into the early morning hours. Temperatures will only
drop a couple of degrees overnight into the lower to mid 40s.

Changes in the pattern Friday with the offshore upper level
ridge weakening. Flow aloft becoming westerly. With no upper
level ridge to fight through offshore the system on Friday will
be the strongest one of the short term. System still looking
progressive and forecasted precipitation values have trended
slightly lower in the last model run. Snow levels rising but
end up not overly high, 5000 feet in the north to 6500 feet in
the south. This will keep some of the water in the mountains in
the form of snow and help reduce the flood threat. Winds picking
up in the afternoon as the front moves into the area but no
advisories look necessary at this point. High temperatures
warming into the lower to mid 50s.

While the surface pressures do not drop very low with the
systems in the short term the very high tide cycle will create
the threat of coastal flooding beginning Thursday on the coast
and Friday over the inland waters. The threat will continue into
the weekend. Felton

&&

.LONG TERM /FRIDAY NIGHT THROUGH TUESDAY/...
Models in good agreement with the front moving out of the area
Friday night into Saturday morning. Ensembles hinting at a very
short pause in the action Saturday afternoon. Warm front arrives
Saturday night with the trailing cold front Sunday. About a
third of the ensemble solutions last night indicated an upper
level ridge building into the area had a chance of deflecting
the next system north into British Columbia Monday. Very few of
the ensembles have the upper level ridge this morning. System
for Monday and Tuesday has a long fetch of moisture extending
way back to 30N/170W. There is a lot of variance in the
ensembles on the rainfall amounts. More details in the hydrology
discussion. For the public forecast rain, breezy and mild both
days. Temperatures Monday through Tuesday in the upper 40s to
mid 50s. Snow levels starting out in the 4500 to 5000 foot range
Monday rising to 5000 to 6500 feet by Tuesday. Felton

&&

.AVIATION...
Northwest flow aloft will continue into Wednesday with a warm
front approaching the area late in the period. A mixed bags of
ceilings out there this morning, with some interior locations
seeing low-end VFR, and places like KOLM seeing LIFR conditions.
With barely any low level flow, can expect lower condition
(MVFR/IFR/LIFR) to likely remain across the board - with
locations seeing VFR to drop down to MVFR. Some minor
improvement to low end VFR is possible across portions of the
interior this afternoon, but is likely to be brief if it does
materialize. Winds are expected to be light and southeasterly
through the period.

KSEA...Low end VFR this morning will likely drop down to MVFR
earlier this afternoon. Ceilings may lift to VFR briefly at
times this afternoon, but confidence in that outcome is low with
flow being so light. Surface winds light northeasterly are
expected to become light and variable overnight then eventually
light S/SE toward morning. Conditions look to then worsen
by early Thursday morning (MVFR/IFR) as a front brings rain and
lower visibilities to the terminal.

Mazurkiewicz

&&

.MARINE...
Surface high pressure over the waters today dissipating
tonight. Front moving through the area Thursday. Stronger front
on Friday. Additional systems will move through the waters over
the weekend into the first half of next week.

Small craft advisory winds in the Strait of Juan de Fuca Friday
into Friday night with gales possible in the Central Strait
Friday night. Small craft advisory winds likely over the inland
waters Friday night. Another round of at least advisory level
winds possible the first part of next week.

Seas remaining below 10 feet through the weekend with the
exception of Friday night where seas will build to 10 or 11
feet. Felton

&&

.HYDROLOGY...
The series of weather systems forecast to reach the area will
eventually increase the threat of river flooding in the coming
days. West northwesterly flow aloft with the system Friday puts
the area of greatest precipitation in the North Central
Washington Cascades. Snow levels rising over 6000 feet.
Precipitation amount forecasts have lowered in the last model
run for Thursday night into Friday with the peak values now under
2 inches. This will ease the pressure on the rivers flowing out
of the area with current hydrographs having the Snoqualmie,
Skykomish, Snohomish and Tolt rivers cresting in action stage at
best.

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

Still a wide variance in the possible precipitation amounts
with the atmospheric river for the first part of next week. The
ECMWF is wetter and less progressive than the GFS Monday and
Tuesday. Models are slowly trending warmer with the snow levels.
Not good for flooding concerns. It is still within the realm of
possibility that we could have a widespread river flooding
event on our hands beginning next Tuesday. With so much
uncertainty all we can say at this point is stay tuned.

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

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...None.
PZ...None.

&&

$$