Seattle, Virginia 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

199
FXUS66 KSEW 220415
AFDSEW

Area Forecast Discussion
National Weather Service Seattle WA
815 PM PST Fri Feb 21 2025

.SYNOPSIS...An atmospheric river will set up over Western
Washington making for a very wet weekend. The river will move out
of the area Sunday night. After a brief break early Monday
a front will move through later Monday into early Tuesday for
another round of rain as well as locally windy conditions. An
upper level ridge will try and build in the middle of next week
but systems nearby will keep a chance of rain at times Wednesday
through Friday especially for the coast.


&&

.SHORT TERM /TONIGHT THROUGH TUESDAY/...The bulk end of the first
wave of precipitation is beginning to move into the Cascades, but
conditions still remain very wet throughout Puget Sound, with
additional showers along the coast. A recent look at the newest
QPF forecast does show some minor increases along the windward
side of the Olympics and portions of the Cascades, but the full
forecast will be run and updated overnight. Otherwise, no
significant changes have been made and an update to the aviation
and marine section can be found below.

An atmospheric river is aimed at Western Washington for the
weekend. Leading edge of the initial slug of moisture reaching the
coast Saturday morning, spreading inland to the Cascades by late
morning. Winds in the lower levels of the air mass increasing with
model 850 mb winds showing a core of southwesterly 50 to 60 knots
over the Southwest Interior and along the coast. Southerly winds
at 850 mb over the North Cascades will give that area less
precipitation than the remainder of the Cascades under the
southwesterly winds aloft scenario. Snow levels rising up to as
high as 7000 feet by late afternoon. Even with rain most of the
day highs will be mild, in the lower to mid 50s.

Atmospheric river remaining over Western Washington Saturday
night. Vertically Integrated Water Vapor Transport ( moisture
content ) numbers the highest during this time frame with models
indicating 1000-1200 kg/m/second. A sustained round of these
values is a strong indicator of river flooding for the area. In
this case the values peak Saturday night into Sunday morning then
ease during the day Sunday. Rainfall amounts of 1.5 to 2 inches in
the 12 hour period between 00z to 12z Sunday ( 4 pm Saturday to 4
am Sunday ) for the mountains and along the coast with 0.50 to
1.25 inches over most of the lowlands. Lower rainfall amounts for
the interior forecast over the Northwest Interior. With the strong
southwesterly flow aloft the rainshadow will be in its usual
place with Sequim and Port Townsend only getting around a quarter
of an inch. Lows in the mid 40s to lower 50s.

Atmospheric river sagging south Sunday morning with rainfall
rates decreasing over Western Washington. Rain increasing again
Sunday afternoon as the river lifts back up over the area. Highs
in the mid 50s.

Front/back end of the atmospheric river moving through Western
Washington later Sunday night into early Monday morning bringing
about an end to the steady rain. Lows in the 40s.

After a brief break Monday morning another weather system
approaches the area Monday afternoon. Parent low with this
feature, a 980-985 mb low, will reach 130W due west of the area
then make a northeasterly turn. This will in turn increase the
negative tilt of the front slowing its northerly progress down
with the front stalling over Western Washington in the afternoon.
With the low that far west best chances for gusty/possible
advisory speed winds, along the coast and the Northwest Interior
late in the day. Highs again in the lower to mid 50s with rain all
afternoon.

.LONG TERM /WEDNESDAY THROUGH SATURDAY/...Extended models in pretty
good agreement with the front kicking out to the north early
Tuesday followed by a weak upper level trough later in the day.
Upper level trough digging south between 130-140W which will in
turn pump an upper level ridge up along the coast Wednesday. Warm
front trying to move through the top of the ridge and with the
cold front well offshore Western Washington will be in the warm
sector. This has the potential to be the warmest day of the season
with highs near 60 in the warmest locations. Trailing cold front
trying to move through the ridge Thursday before the ridge
rebuilds Friday. Operational runs showing good amplitude to the
ridge but the ensemble solutions are not as strong. This keeps a
chance of rain at times in the forecast Wednesday through Friday
with the best chances along the coast and over the Northwest
Interior. Mild air mass remaining over the area with highs Thursday
and Friday in the mid 50s to near 60. Felton


&&

.AVIATION... Ceilings will lower to MVFR tonight and look to
remain there through the remainder of the TAF period.
Southeasterly winds will increase tonight ahead of the frontal
system, with the strongest winds (up to 12-15 kt) in the north
interior. Winds remain south to southeasterly tomorrow and will
begin to increase area-wide tomorrow afternoon as another round of
rain begins to approach the region.


KSEA...Ceilings have lowered to MVFR in recent observations and
are expected to persist in the wake of this first pulse of
moisture and persisting through the remainder of the TAF period.
Southeasterly winds will remain around 7 to 10 knots through
tonight and will begin to continue to increase tomorrow afternoon
at the end of the TAF period. As the front passes, there is LLWS
potential, but confidence is too low and the event too far out to
be considered in this TAF package, but will be evaluated
throughout the night.

62/Kristell

62


&&

.MARINE...A frontal system will continue to move onshore tonight
into early Saturday morning, with a series of frontal systems
traversing the area waters Saturday and late Sunday. This will keep
conditions active across the area waters. Small Craft Advisory
conditions will continue across the coastal waters today, with a
brief break tonight before winds restrengthen on Saturday, reaching
low-end gale force by Saturday afternoon. Through the interior
waters, southeasterly winds will strengthen through Admiralty Inlet,
the East Entrance to the Strait of Juan de Fuca, and through
portions of the Northern Inland Waters. There will also be a brief
break early tomorrow morning before winds strengthen again Saturday
afternoon into early Sunday. There may be some gusts to gale force
through the East Entrance on Saturday, but sustained winds should
remain in the Small Craft range. Winds look to ease below thresholds
across the interior waters on Sunday but remain elevated over the
coastal waters with the system on Sunday farther offshore.

A stronger low pressure system looks to develop over the northeast
Pacific and move northeastward towards Vancouver Island Monday night
into Tuesday. There still remains considerable uncertainty on the
strength and track of this system, but a period of gale to
potentially storm force winds remain possible during this period.
High pressure looks to develop over the Pacific Northwest by the
middle of next week, for a period of calmer conditions.

Seas will slowly build this evening to around 12 to 15 ft tonight.
Seas will increase and subside with each passing system this weekend
but generally remain in the 12 to 15 ft range. The stronger system
Monday into Tuesday may push seas over 20 ft Monday night. Seas will
slowly subside after Tuesday but look to remain above 10 ft through
at least mid-week.

62


&&

.HYDROLOGY...A series of systems including an atmospheric river
will move through the area into Tuesday. This has increased the
potential for river flooding, urban flooding, and landslides. Snow
levels will increase to above 7000 feet Saturday night into
Sunday, with heavy rain falling over the Cascades and Olympics.
These mountain ranges will likely see 3 to 5 inches of rain, with
locally higher amounts possible.

A few of the rivers remain on track to reach flood stage at some
point over the weekend into next week. The flood watch for Mason
County was upgraded to a flood warning for the Skokomish River at
Potlatch (moderate flooding forecasted). A flood watch for Sunday
morning through Tuesday was issued for Grays Harbor, Lewis,
Thurston, Pierce, King, Snohomish, and Skagit Counties based on
the 10-15% increase in QPF over these areas. Several of the rivers
expected to go well above action stage (Snoqualmie at Carnation
is projected to go into minor flood Monday morning). A flood
potential outlook remains for Jefferson, Clallam and Whatcom
counties. Flood potential is too low for these areas to be
included in the flood watch. There is still the possibility of
urban flooding across all of the area with the best chance
Saturday night into Sunday morning.

Please continue to monitor the forecast for any potential changes to
the precipitation outlook through the weekend, and for any headline
changes.

HPR


&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...Flood Watch from Sunday morning through late Tuesday night for
     Bellevue and Vicinity-Central Coast-East Puget Sound
     Lowlands-Everett and Vicinity-Lower Chehalis Valley Area-
     Olympics-Seattle and Vicinity-Southwest Interior-Tacoma
     Area-West Slopes North Cascades and Passes-West Slopes
     North Central Cascades and Passes-West Slopes South Central
     Cascades and Passes-Western Skagit County.

     Wind Advisory from 10 AM to 7 PM PST Saturday for Central Coast-
     North Coast.

PZ...Small Craft Advisory until 7 PM PST Saturday for Admiralty Inlet-
     East Entrance U.S. Waters Strait Of Juan De Fuca-Grays
     Harbor Bar-Northern Inland Waters Including The San Juan
     Islands-West Entrance U.S. Waters Strait Of Juan De Fuca.

     Small Craft Advisory until 4 AM PST Saturday 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.

     Gale Warning from 4 AM to 7 PM PST Saturday 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.

&&

$$