Brier Weather Station
Latitude N 47° 46' 49" Longitude W 122° 16' 48" Elevation 341 ft
684
FXUS66 KSEW 201045
AFDSEW
Area Forecast Discussion
National Weather Service Seattle WA
345 AM PDT Fri Mar 20 2026
.SYNOPSIS...
Atmospheric river that has been over Western Washington the
past few days moving out this afternoon as the cold front that
has been stalled over Vancouver Island finally moves through the
area. Cooler air mass behind the front for tonight and Saturday.
Weak system going by to the north Sunday. Additional weather
systems Tuesday and Wednesday. Upper level ridge trying to build
Thursday.
&&
.SHORT TERM /TODAY THROUGH SUNDAY/...
Satellite imagery shows what it has showed for the last few
mornings, an atmospheric river over Western Washington. Doppler
radar has rain over most of the area with a bit of a rain shadow
over the Central Puget Sound. Temperatures at 3 am/10z were
in the lower to mid 50s.
Atmospheric river on its last legs with the cold front stalled
over Vancouver Island kicking it in gear this afternoon and
moving through Western Washington ending the river. Rain most
of the day. Breezy conditions developing just ahead and with the
front. Decent westerly push behind the front down the Strait of
Juan de Fuca late this afternoon. High temperatures will occur
this morning with temperatures cooling later this afternoon.
Highs in the 50s.
Cooler air mass moving into Western Washington this evening with
snow levels dropping to 3500 to 4000 feet. Post frontal showers
will decrease overnight. Convergence zone developing over
Snohomish county will dissipate overnight as well. Much cooler
with Saturday morning lows in the mid 30s to lower 40s.
Not much going on Saturday with zonal flow aloft over the area.
Air mass still slightly unstable keeping the threat of showers
in the forecast but it will be dry for most of the day. Snow
levels continuing to fall bottoming out around 2000 feet.
Moisture is limited so not expecting much, if any, new snow in
the mountains. Highs colder than the current temperatures, mid
40s to lower 50s.
Much weaker system approaching the north coast Saturday night
with the best chance for any precipitation right along the
coast. Lows mostly in the 30s. The colder locations could get
down to near freezing.
Weak system moving by to the north Sunday giving the area a
chance of rain. Highs will remain cool, a couple of degrees
either side of 50. Felton
&&
.LONG TERM /SUNDAY NIGHT THROUGH THURSDAY/...
Short dry spell Sunday night into Monday with a weak upper level
ridge ahead of the next system. Model timing of this feature has
been bouncing around between the rain arriving Monday night or
Tuesday morning. Most of the solutions are back to the Tuesday
morning scenario. This system is associated with a deep 965 mb
low. The low is well north in the Gulf of Alaska so not
forecasting any impactful winds with the front. Another system
Wednesday before an upper level ridge tries to build over
Western Washington Thursday. Models currently indicating this
could be the start of a small, 3 or 4 day, dry spell.
Temperatures remaining a little below normal with highs in the
lower to mid 50s and lows in the mid 30s to lower 40s.
&&
.AVIATION...
Moist west to southwest flow aloft continues across Western
Washington today as a frontal system offshore approaches the region.
The front will sweep onshore late this afternoon with increasing low
level onshore flow in its wake. A weak Puget Sound Convergence Zone
may linger into this evening. Widespread MVFR ceilings in rain will
continue into early afternoon before turning into post-frontal
showers after around 22Z. Some improvement to VFR is expected behind
the front late this afternoon and evening, but a few pockets of MVFR
may persist in and around convergence zone activity.
KSEA...MVFR in rain is expected through around 21Z before
precipitation turns to a few showers behind the front. Ceilings are
expected to lift to lower end VFR by around 23Z and continue into
the evening. Surface winds southerly 6 to 10 knots will rise to
southwesterly 10 to 20 knots with the arrival of the front this
afternoon. A transition to N/NE surface winds of 8 knots or less is
presently expected to reach the terminal in the 01Z-03Z window this
evening.
27
&&
.MARINE...
A front will move onshore later today with increasing onshore flow
behind it. A surface ridge will slide eastward across the waters
over the weekend. A strong frontal system will reach the waters
Monday night into Tuesday.
Coastal seas are expected to remain generally under 10 feet into
Monday before a sub-990 millibar low passing over the offshore
waters generates another round of double digit seas.
27
&&
.HYDROLOGY...
The end is finally in sight for the atmospheric river over
Western Washington. Cold front moving through this afternoon
bringing about an end to the river. Even with the river`s demise
another 1 to 1.5 inches of rain in the Olympics and North and
Central Cascades today and tonight. Snow levels will drop
significantly behind the front keeping some of this moisture in
the mountains in the form of snow overnight.
Flood warnings already out for the Snoqualmie, Snohomish, Tolt
Skykomish and Skagit rivers. The Stillaguamish, Skokomish and
possibly the Cedar river could be added to this list later
today.
Colder air mass moving into the area tonight and Saturday with
no hydrologically significant precipitation. Flood crests
moving downstream with the upper reaches of the rivers cresting
tonight and the lower reaches Saturday. By Sunday all of the
rivers are forecast to be back in their banks. Felton
&&
.SEW WATCHES/WARNINGS/ADVISORIES...
WA...Flood Watch through this afternoon for Cascades of Snohomish
and Northern King Counties-Cascades of Southern King
County-Cascades of Whatcom and Skagit Counties-City of
Seattle-Downtown Everett / Marysville Area-Eastside-
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 the North Cascades-
Foothills of the Western and Southern Olympic Peninsula-
Lowlands of Pierce and Southern King Counties-Lowlands of
Western Skagit and Northwestern Snohomish Counties-
Lowlands of Western Whatcom County-Middle Chehalis River
Valley-Olympia and Southern Puget Sound-Olympics-
Shoreline / Lynnwood / South Everett Area-Southern Hood
Canal-Willapa and Black Hills.
PZ...Small Craft Advisory from 2 PM this afternoon to 11 AM PDT
Saturday for West Entrance U.S. Waters Strait Of Juan De
Fuca.
Gale Warning from 4 PM this afternoon to 3 AM PDT Saturday for
Central U.S. Waters Strait Of Juan De Fuca-East Entrance
U.S. Waters Strait Of Juan De Fuca.
Small Craft Advisory from 5 PM this afternoon to 11 AM PDT
Saturday for Admiralty Inlet.
Small Craft Advisory until 5 PM PDT this afternoon for Puget
Sound and Hood Canal.
Small Craft Advisory until 5 AM PDT 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.
&&
$$
NWS SEW Office Area Forecast Discussion