523
FXUS66 KSEW 240429
AFDSEW

Area Forecast Discussion
National Weather Service Seattle WA
829 PM PST Tue Dec 23 2025

.UPDATE...High wind watches have been upgraded to warnings
across much of the interior lowlands of western Washington. For
the foothills, we opted to go with advisories and begin them
early tomorrow morning as gap winds with gusts of up to around
45 mph will be possible for the Cascade valleys and foothills.
Guidance has been consistent on the coast staying below
thresholds, so the watch has been cancelled there. There may be
some gusts up to 45 mph in the morning with the easterlies, but
the actual low core is not compact enough to forecast
significant winds on the coast tomorrow afternoon. We will
continue to watch as this low feature currently offshore of San
Francisco continues to work its way NNW overnight into tomorrow
morning. For more details on the forecast and the dynamics at
play, see below. 62

&&

.SYNOPSIS...
Quiescent weather is expected this afternoon, with more activity
expected tomorrow. A deepening low pressure system will be
moving up along the coast into western Washington tomorrow,
favoring strong wind potential in Puget Sound and along the
coast, in addition to some rainfall. Unsettled weather is
expected again this weekend and into early next week.

&&

.SHORT TERM /TONIGHT THROUGH THURSDAY NIGHT/...
The primary weather feature to watch in the short term will be
the low pressure system moving up from the south tomorrow. As it
moves north and strengthens, wind gusts have increased in the
forecast though uncertainty still remains. For more on that, see
the wind section of this discussion here:

Wind: A compact low pressure system developing along the northern
California coast this evening will lift northward toward the Pacific
Northwest on Wednesday. Models continue to struggle with the path
and subsequent strength of the surface low as it approaches Western
Washington midday Wednesday. Morning runs of the HREF and REFS
continued to show mean gusts of 45-50 mph through Puget Sound as
well as coastal areas by early to mid afternoon Wednesday with 90th
percentile data showing gusts in the realm of 60 mph. As with many
high wind producing storm systems (i.e. last week), deference is
also given to the rate of change of surface pressure and
topographically driven contributions. As of this morning,
isallobaric plots from both the GFS and NAM were still showing 8 to
12 millibars of pressure rise in just 3 hours through a swath of the
coast and Puget Sound on Wednesday afternoon. Funneling that through
a north/south oriented channel like Puget Sound can act to enhance
the wind...especially when 850 millibar winds are roughly from the
same direction at 60+ knots. Given the ongoing uncertainty, a high
wind watch has been issued for much of the lowlands and will let
following shifts decide on warnings versus advisories. 27

In addition to the wind, there will also be some rain with this
system, but amounts aren`t looking particularly impressive. A
few tenths of an inch up to a quarter inch throughout Puget
Sound and around an inch in the north Cascades and portions of
the Olympics. In the context of the last few weeks, certainly
not impactful rain amounts. Additional, light rain amounts are
expected Thursday, with calmer weather expected over the
weekend.

21

&&

.LONG TERM /FRIDAY THROUGH TUESDAY/...
Upper level ridging appears to be the favored forecast solution
late in the week into the weekend, which would be a welcome
break from the last few weeks of intense activity. This reprieve
will be relatively short lived as unsettled weather is favored
in the week two timeframe from the CPC. There is potential for
more atmospheric river activity in this period, but there is not
solid confidence on this as of now.

21

&&

.AVIATION...
VFR cigs prevail for all terminals this evening with
light ENE winds, except for OLM with patchy low clouds. Rain
will be reintroduced to most terminals late tonight around 09Z.
Locations that could see reductions overnight to MVFR and/or IFR
include OLM and PWT for stratus and low cigs. ESE winds will
increase tomorrow morning generally around 12Z, but there is a
sharp increase and direction change to southerly in the early
afternoon that will affect all terminals. High end gusts in
Puget Sound could near 45-50 kts between 20Z-01Z.

KSEA...VFR and light winds presently at the terminal. These
conditions are likely to linger throughout the evening, with an
expected increase in the ESE winds to 8-10 kts beginning after
06Z. Rain chances return after 09Z as the next system
approaches. Expect ESE gusts to 20-25 kts to begin after 14Z,
and a rapid shift and increase to S winds after 19Z. Confidence
has grown in gusts reaching 45-50 kts at the terminal tomorrow
afternoon.

33/21

&&

.MARINE...
A strong surface low pressure system is expected to lift northward
across the coastal waters or Olympic Peninsula on Wednesday. This is
expected to produce gales across nearly all area waters. A broad
surface trough will remain to the southwest of the area and high
pressure over interior British Columbia for a period of northerly
flow on Thursday into Friday. Surface high pressure will build over
the waters this weekend for a quieter period of weather.

Seas will subside below 10 feet tonight into Wednesday. Seas may
briefly approach 10 feet Wednesday afternoon into Wednesday night,
but generally are expected to remain below 10 feet into the end of
the week.

27

&&

.HYDROLOGY...
Rivers across western Washington continue to trend
downward as precipitation across the region lightens up. Additional
rainfall throughout the week is not expected to cause any
additional rises to area rivers. Additionally, the threat of
landslides has decreased across western Washington.

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...Coastal Flood Advisory from 6 AM to noon PST Wednesday for
     City of Seattle-Downtown Everett / Marysville Area-Island
     County-Lowlands of Pierce and Southern King Counties-
     Lowlands of Western Skagit and Northwestern Snohomish
     Counties-Lowlands of Western Whatcom County-San Juan
     County-Shoreline / Lynnwood / South Everett Area.

     High Wind Warning from 1 PM to 7 PM PST Wednesday for Downtown
     Everett / Marysville Area-Island County-Lowlands of
     Western Skagit and Northwestern Snohomish Counties-
     Lowlands of Western Whatcom County-Port Townsend Area-San
     Juan County.

     Wind Advisory from 4 AM to 7 PM PST Wednesday for 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.

     High Wind Warning from 10 AM to 7 PM PST Wednesday for City of
     Seattle-Eastern Kitsap County-Eastside-Lowlands of Lewis
     and Southern Thurston Counties-Lowlands of Pierce and
     Southern King Counties-Middle Chehalis River Valley-
     Northern Hood Canal-Olympia and Southern Puget Sound-
     Shoreline / Lynnwood / South Everett Area-Southern Hood
     Canal-Willapa and Black Hills.

PZ...Gale Warning from 1 AM Wednesday to 1 AM PST Thursday 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-West
     Entrance U.S. Waters Strait Of Juan De Fuca.

     Small Craft Advisory from 1 AM Wednesday to 1 AM PST Thursday
     for Central U.S. Waters Strait Of Juan De Fuca.

     Gale Warning from 9 AM Wednesday to midnight PST Wednesday
     night for Admiralty Inlet-East Entrance U.S. Waters
     Strait Of Juan De Fuca-Northern Inland Waters Including
     The San Juan Islands.

     Gale Warning from 9 AM to 10 PM PST Wednesday for Puget Sound
     and Hood Canal.

&&

$$