974
FXUS66 KSEW 011110
AFDSEW

Area Forecast Discussion
National Weather Service Seattle WA
310 AM PST Mon Dec 1 2025

.SYNOPSIS...Weak weather systems moving down the backside of an
upper level ridge offshore will move through Western Washington
the next few days. One will arrive this morning with another
one later tonight into Tuesday. A third weak system will arrive
Thursday. The ridge offshore will weaken Thursday night opening
the door for a series of stronger systems to reach the area
Friday into the first part of next week.

&&

.SHORT TERM /TODAY THROUGH WEDNESDAY/...
Satellite imagery shows weak upper level ridge off the coast
with a weak weather system moving down the backside of the
ridge through British Columbia. High clouds over the area. Clear
skies Sunday evening allowed fog to form over the Southwest
Interior with visibility at Olympia and Chehalis a half mile or
less at 3 am/11z. Temperatures were mostly in the 30s.

Weak system moving through Western Washington this morning.
Doppler radar is picking up some echoes over the Northwest
Interior but with cloud heights above 10000 feet very little if
any of the precipitation is reaching the ground. This will
continue to be the case as the system moves through the area.
With temperatures near freezing in the Northwest Interior if any
precipitation does reach the ground in the next few hours could
see a few snow flakes/flurries in both Whatcom and Skagit
county. For the remainder of the area just a chance of light
rain. Fog in the Southwest Interior will dissipate later this
morning. Cloud cover will keep high temperatures in the mid 40s.


Another system will follow the same track tonight moving into
the area overnight into the early morning hours. This system is
a little stronger than the one this morning and actually carves
out a bit of a trough with it. Likely pops common across the
area but rainfall amounts will be light, less than a tenth of an
inch for most locations. Cloud cover will keep temperatures from
dropping tonight into Tuesday morning with lows just a few
degrees below the highs, upper 30s to mid 40s.

System moving out of the area from north to south later Tuesday
morning into Tuesday afternoon. Dry afternoon from Seattle
northward. Not much clearing behind the front keeping skies
mostly cloudy in the afternoon. Best chances for a little
clearing along the North Coast. Highs in the mid 40s to lower
50s.

Upper level ridge offshore nosing into the British Columbia
coast Tuesday night and Wednesday with dry northerly flow aloft
over Western Washington. Light flow in the lower levels combined
with the ridge axis offshore will keep skies mostly cloudy. The
cloud cover will limit fog formation with just patchy fog in
the fog prone locations like the Southwest Interior Tuesday
night and wednesday morning. Lows in the mid 30s to lower 40s.
Cloud cover will also keep high temperatures down, mostly in the
mid 40s.

November in Seattle was a warm one. The average monthly
temperature of 48.6 degrees was 2.1 degrees above normal. This
is the 7th warmest November in 81 years of records. The normal
average temperature in Seattle for December is 42.0 degrees. In
the top 10 warmest Novembers not including this year 8 out of
the 10 Decembers had an average temperature below 42.0 degrees.
Felton

&&

.LONG TERM /WEDNESDAY NIGHT THROUGH SUNDAY/...
Extended models and ensembles in good agreement with another
weak system moving down the backside of the ridge into Western
Washington Thursday. Ridge offshore weakening Thursday night
opening the door to a series of stronger systems. The first
one arriving Friday with another later in the weekend. The
system on Friday could tap into some sub tropical moisture. Air
mass over the area not excessively warm, snow levels in the 5000
to 6000 foot range, keeping some of the precipitation in the
mountains in the form of snow. Snow levels slowly lowering over
the weekend and could be below the higher passes for the round
of precipitation later in the weekend. High temperatures in the
40s Thursday will warm a little into the lower 50s for the
remainder of the period. Felton

&&

.AVIATION...
A ridge will move out of the region this morning as a
weak shortwave trough and front sweep through the region Today into
Tuesday. Flow aloft will remain northwesterly. Radar has showers
moving south across the Canadian border this morning (this will
primarily affect the northern terminals). Skies are a bit clearer to
the south still ahead of the front. The Chehalis Valley remains the
primary fog/freezing fog location this morning (between KOLM and
KCLS). Satellite/cameras are also showing a few thin patchy fog
layers forming (mainly near rivers and cool/sheltered areas) up to
Puget Sound and some of the central terminals that are not yet
covered with high clouds. This keeps a chance of brief patchy
fog/mist possible for central and southern terminals through 18Z as
ceilings continue to fill in from the north through the morning.
Expect ceilings to gradually lower from VFR down to MVFR from north
to south this evening overnight to Tuesday as showers move through.
There is also a 40% that the ceilings may dip into IFR criteria
Tuesday morning (from Kitsap/Puget Sound through the south interior
and Cascades). Calm/light north winds this morning under 5 kt will
flip to the south 4-8 kt this evening, returning to the northwest
Tuesday morning.

KSEA...Odds remain very low for fog impacting the terminal this
morning (although thin patchy fog has been observed to the northeast
of the terminal, but it may stay close to the Green River and go
through KBFI to the north). Weak front brings a 30% chance of
showers to the terminal area this afternoon. Ceilings will gradually
lower through the day, with MVFR expected after 03Z Tuesday. There
is a 30% chance ceilings may drop below 1,000 ft Tuesday morning.
Winds light out of the northeast this morning 3-6 kt will shift to
south this afternoon and increase to 4-8 kt overnight, before
turning back to the northwest 3-6 kt Tuesday morning.

HPR

&&

.MARINE...
High pressure will move out of the region today as a weak
system moves over the waters today through Tuesday with showers.
Northwest winds behind the system Tuesday will increase in the
coastal waters with winds of 15-25 kt (especially in the outer
coastal waters). Seas will also increase from 4-6 ft Monday to 9-12
ft Tuesday through Wednesday. Benign conditions are expected behind
this system, with light winds, and seas returning to 4-6 ft. A
stronger system Friday through the weekend may bring small craft
advisory level winds to the coastal waters, and a few of the north
interior waters. There is also a medium chance at this time for gale
winds in the Strait of Juan de Fuca. Seas will also increase to 9-13
ft with this system Friday through the weekend into early next week.

HPR

&&

.HYDROLOGY...
System reaching the area around Friday looks to possibly have
some sub tropical moisture entrained with it. The pattern is
progressive and snow levels are not excessively high, 5000 to
6000 feet. River flooding is not expected over the next 7 days.

November rainfall for Seattle was 5.71 inches, 0.60 inches
below normal. Only March and August have had above normal
rainfall this year. The yearly rain total for Seattle through
November 30th is 25.68 inches. The 8th driest January through
November in 81 years of records and the driest since 2002 with
25.38 inches. There have only been 6 years since records started
in 1945 where the yearly rainfall total in Seattle has been
less than 30 inches. The last time was 2000 with 28.66 inches.
Felton

&&

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

&&

$$