638
FXUS66 KSEW 221100
AFDSEW

Area Forecast Discussion
National Weather Service Seattle WA
300 AM PST Mon Dec 22 2025

.SYNOPSIS...A frontal system will move across Western Washington
this afternoon into tonight for increasing precipitation and
breezy winds. A brief break in precipitation is possible
Tuesday. A strengthening surface low tracking northwards will
bring widespread precipitation on Wednesday, with the potential
for gusty winds. Unsettled weather will continue Thursday into
late week with troughing over the Western US.

&&

.SHORT TERM /TODAY THROUGH WEDNESDAY/...A mix of clouds and some
clearing early this morning with continued lingering showers,
especially along the coast. Another frontal system will approach
Western Washington offshore this morning, and move across the
area midday through this evening. Steadier precipitation will
increase along the Olympic Peninsula midday, and move into the
interior later this afternoon. Increasing southerly winds
expected with this frontal passage. Wind gusts are expected to
range 35 to 45 MPH for the coast, as well as Hood Canal
northwards. A Wind Advisory remains in effect for these areas,
with gusts peaking this afternoon. Breezy conditions will exist
elsewhere, with gusts ranging 25 to 40 MPH. Local tree limb
damage and power outages are possible. In addition to the wind,
heavier mountain snowfall will occur with the front, with the
heaviest snowfall amounts near Mt. Baker. The Winter Storm
Warning for the North Cascades has been extended through this
evening, with a Winter Weather Advisory in place for the
Olympics. Snow rates will peak for the Cascade Passes late
afternoon through this evening, with 3 to 6 inches of snow for
Snoqualmie Pass. Post-frontal showers will linger on Tuesday,
especially for the Olympic Peninsula and Cascades, with a brief
period of drier weather for the interior.

The next surface low that will impact the area is expected to
strengthen rapidly offshore of northern California Tuesday
night, and track northwards on Wednesday. This system will be
associated with a deepening upper trough offshore of the
Western US. There has been a steady trend in 00z/06z ensembles
(particularly in GEFS/EPS) showing a stronger system in the
vicinity of Western Washington between 18z Wednesday-00z
Thursday. The 00z EPS probabilities of sub 990mb MSLP peaks 18z
Wednesday near UIL between 70-80%, with probs around 30-40% for
GEFS, both an increase from their prior counterparts on 12z
Sunday guidance. With that said, there continues to remain quite
a spread in extent and magnitude of winds in the individual
ensemble members. For example.. the 10-90th percentile max wind
gusts for SEA (from EPS) on Wednesday range 7 to 60 MPH, a
spread of 53 MPH for an event less than 72 hours out. The
uncertainty can also be seen well on the UWWRF GFS ensembles,
ranging from a sub 985 MB low offshore of WA/OR to relatively
calm winds due to a weaker system or eastward track. Given the
high level of uncertainty, it will remain extremely important to
monitor the forecast over the next few days, particularly given
the antecedent soil moisture if a windier solution occurs.

Due to the variability in guidance, uncertainty also exists as
to the extent of QPF on Wednesday, and the snow levels over the
Cascades. The 25th to 75th spread on NBM for snow levels range
2500 to 4500 feet over the central Cascades during the bulk of
the precipitation. With that said, the risk for additional snow
is expected on Wednesday for all Cascade Passes, with total
snowfall amounts generally up to 4" at this time. Those
traveling over the Cascade Passes should continue to monitor the
forecast.

&&

.LONG TERM /WEDNESDAY NIGHT THROUGH SUNDAY/...The aforementioned
surface low will continue to track northwards and weaken into
British Columbia Wednesday night. Additional precipitation,
albeit lighter in amounts, looks to spread northwards into
Western Washington Thursday with continued unsettled weather
late week due to troughing offshore. Snow levels look to also
lower Friday into Saturday, particularly near the BC border and
Cascade Foothills with lingering showers. Weak ridging then
may build into Western Washington next weekend, although a
transition to more westerly flow may allow for continued
precipitation, especially for the mountains and near BC. A
cooler airmass is likely Thursday into Friday before slight
warming next weekend. JD

&&

.AVIATION...Southwesterly flow will continue throughout the day
today and into Tuesday as an upper level trough along the Canadian
coast digs deeper south. A series of systems circulating through
this system will bring ebbs and flows to surface winds in W WA for
the first half of next week. The next of which will see wind speeds
increasing and becoming gusty around noon or just a little before.
For the morning, winds are generally southerly with speeds 5-10 kts,
however some terminals have gone to light and variable at times this
early morning. Once speeds increase, direction will remain southerly
but speeds ramp up to 10-15 kts with gusts to 25 kt. More wind prone
terminals such as HQM and BLI could see even greater speeds ranging
15-20 kts with gusts to 30 kts. Strongest winds will be expected
along the coast, in the San Juan Islands and along the coast of
western Whatcom county.

Majority of terminals showing VFR conditions this early morning
although there are isolated patches of MVFR to IFR conditions,
especially PWT and OLM, which are more prone to lower cigs and fog.
Cigs do lower as winds start to ramp up in advance of incoming
system but are expected to remain VFR into the early afternoon
before lowering to MVFR conditions around or a little before sunset.
Naturally, this is when precip will return to the area. Rains should
begin to wrap up tonight between 10 PM PST and midnight. As this
happens, winds ease slightly...allowing cigs to sink a little bit
more but most locations should remain MVFR into the overnight
period.

KSEA...VFR conditions at the time of this writing. Above discussion
pertaining to both winds and cigs applies. Winds pick up around 19Z
but remain southerly...ranging 10-15 kts with gusts up to 25 kts.
Clouds will start to fill in in the late morning with cigs generally
3000-4000 ft by noon. Further lowering around 00Z into MVFR range.
Winds ease around 06Z, which will allow cigs to lower slightly,
still remaining mid-range MVFR.

18

&&

.MARINE...Stronger winds will develop over the waters as the
next system moves into the area starting this morning. Inherited
Gale Warnings and Small Craft Advisories look good and remain
in effect. The flow will turn northerly on Tuesday or Tuesday
night in response to low pressure off California. This feature
may pass through western Washington on Wednesday. North winds
return on Thursday as another low forms to our south. 18/33

&&

.HYDROLOGY...Rivers remain on a downward trend although a
handful of rivers could see slight rises due to rains associated
with the incoming weather system today. Any rises will fall
quickly, possibly as early as tonight but more likely Tuesday
morning. The only river that will see flooding beyond today is
the Skokomish River in Mason County.

18

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...Coastal Flood Advisory from 6 AM this morning to noon PST
     today for San Juan County.

     Wind Advisory from 10 AM this morning to 7 PM PST this evening
     for Island County-Lowlands of Western Skagit and
     Northwestern Snohomish Counties-Lowlands of Western
     Whatcom County-Port Townsend Area-San Juan County.

     Winter Storm Warning until 10 PM PST this evening for Cascades
     of Whatcom and Skagit Counties.

     Winter Weather Advisory until 4 AM PST early this morning for
     Cascades of Pierce and Lewis Counties-Cascades of
     Snohomish and Northern King Counties-Cascades of Southern
     King County.

     Winter Weather Advisory until 10 PM PST this evening for
     Olympics.

     Wind Advisory from 10 AM this morning to 4 PM PST this
     afternoon for Grays Harbor County Coast-Northern
     Washington Coast.

PZ...Small Craft Advisory from 1 PM this afternoon to 10 AM PST
     Tuesday for Grays Harbor Bar.

     Small Craft Advisory until 4 AM PST Tuesday for Admiralty
     Inlet-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 from 10 AM this morning to 4 AM PST
     Tuesday for Central U.S. Waters Strait Of Juan De Fuca.

     Gale Warning until 10 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-East Entrance U.S.
     Waters Strait Of Juan De Fuca.

&&

$$