Brier Weather Station
Latitude N 47° 46' 49" Longitude W 122° 16' 48" Elevation 341 ft
496
FXUS66 KSEW 210920
AFDSEW
Area Forecast Discussion
National Weather Service Seattle WA
220 AM PDT Tue Apr 21 2026
.SYNOPSIS...
Cooler and wetter conditions will settle over the region through
the middle of the week, with chances for thunderstorms this
afternoon over the Cascades. Drier and more seasonable
conditions will return by the end of the week and into the
weekend as a high pressure ridge builds offshore.
&&
.SHORT TERM /TODAY THROUGH THURSDAY/...
An upper level low pressure system will slowly progress inland
over Oregon throughout much of the week, bringing in cooler
temperatures alongside periods of rain. Wrap around moisture has
already made its way northward into southwestern Washington this
morning with light accumulations. Showers will continue to move
northward into the region throughout the day today. Temperatures
will cool considerably today as this system works its way into
the region, with highs reaching the mid 50s to low 60s.
Instability from the aforementioned low may also produce some
lightning strikes over the western Cascades this afternoon, but
any thunderstorms are unlikely over the lowlands.
The upper level low will continue to meander eastward towards
the Intermountain West on Wednesday, maintaining chances for
shower activity and cooler temperatures. Wednesday will be the
coolest day of the week, with temperatures mostly peaking below
the 60 degree mark across western Washington. Snow levels will
remain above 5000 to 6000 feet through mid week, limiting any
snow accumulation to the higher mountain peaks.
Conditions will dry out for much of the region on Thursday as
moist northwest flow develops aloft, with light showers
tapering off over the Cascades. Temperatures across the region
will begin to rebound, with highs reaching the upper 50s to
lower 60s. Cloudy skies Thursday morning will give way to mostly
sunny skies by the late afternoon.
&&
.LONG TERM /THURSDAY NIGHT THROUGH MONDAY/...
Forecast models continue to show an upper level ridge building
offshore through the extended, though models are showing
variability over how far eastward the high pressure will expand.
Northerly flow aloft will maintain seasonable temperatures
through the weekend, though both ensembles and deterministic
models are hinting at the potential for showers to develop on
Sunday and Monday as a positively tilted trough brushes the
eastern edge of the high pressure ridge.
15
&&
.AVIATION...
South to southeasterly flow aloft remain in place over W WA as a
cutoff upper level low off the northern California coast gradually
shifts eastward. Surface winds have largely shifted south to
southwesterly over most terminals, although some have gone light and
variable. Little variation in direction for much of the TAF period
for most terminals, although CLM and PAE, being more susceptible to
influence from the Strait, could see a more northwesterly direction
emerge late this afternoon/early this evening. Speeds expected to
increase areawide by late this morning, generally ranging 8-12 kts.
VFR conditions in place this early morning and will continue
throughout the remainder of the morning, possibly into the early
afternoon. Cigs will continue to lower throughout the day as the
combination of the aforementioned upper low cycling moisture into
the area with onshore flow returning, also adding moisture, allows
for an increase in low-level cloudiness. Widespread MVFR conditions
expected to emerge this afternoon, however some sites could see them
sneak in as early as late morning, such as terminals more prone to
lower cigs /HQM, OLM and PWT/. Showers expected over the area late
this afternoon or early this evening and that risk will extend into
tonight. Activity is expected to taper off during the overnight
hours, although lower cigs will remain in place.
KSEA...VFR conditions will continue for much of the early morning
period and likely into mid-morning before MVFR conditions likely
hold off until late morning/early afternoon...as latest obs and
model solutions have backed off on inherited aggressive timing.
Afternoon shower development still on track, with precip at the
terminal still expected in the late afternoon and into the evening
before activity tapers off overnight. Even though rain ends, plenty
of low-level moisture will keep cigs MVFR for the remainder of the
TAF period. Surface winds S/SW 4 to 8 knots this morning before
rising to 8 to 12 knots this afternoon and into the overnight .
period.
18
&&
.MARINE...
Weak low pressure will remain over the inner coastal and interior
waters into midweek with broad high pressure remaining well
offshore. A modest increase in onshore flow today may be enough to
boost winds in the Central and Eastern Strait to low-end SCA
criteria. As such, left inherited headline in place. Gusty north to
northwesterly winds and steepening seas are expected over the outer
coastal waters on Wednesday. Models have been very consistent over
the past 72 hours /at least/ that seas are likely to exceed 10 ft
over the majority of the Coastal zones. Given that level of
confidence and in collaboration with PQR, went ahead and issued an
SCA to cover this event. Although winds increase, SCA thresholds for
wind are only met out in the outer coastal waters. Rough bar
conditions may emerge for Grays Harbor bar Wednesday evening, but
with that being 4 periods out /today, tonight, tomorrow, tomorrow
night/, felt it best to leave that potential headline to future
shifts. Winds ease, seas subside and the flow turns more northerly
late this week in response to a strengthening surface ridge over
British Columbia.
18/27
&&
.HYDROLOGY...
No river flooding is expected over the next 7 days.
&&
.SEW WATCHES/WARNINGS/ADVISORIES...
WA...None.
PZ...Small Craft Advisory from 3 PM this afternoon to 11 PM PDT
this evening for Central U.S. Waters Strait Of Juan De
Fuca-East Entrance U.S. Waters Strait Of Juan De Fuca.
Small Craft Advisory from 11 AM Wednesday to 11 AM PDT
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.
&&
$$
NWS SEW Office Area Forecast Discussion