Brier Weather Station
Latitude N 47° 46' 49" Longitude W 122° 16' 48" Elevation 341 ft
340
FXUS66 KSEW 211557
AFDSEW
Area Forecast Discussion
National Weather Service Seattle WA
857 AM PDT Mon Sep 21 2026
.SYNOPSIS...
Upper level ridge well to the east with an upper level trough
offshore today. Weak system moving by to the north this
afternoon. Convergence zone possible over the Central Puget
Sound late tonight into Tuesday morning. Next system spinning
out of the trough dissipating as it reaches the area Wednesday.
Stronger system arriving Thursday night into Friday morning.
Flat upper level ridge over Western Washington next weekend with
a warm front dissipating off the coast Sunday.
&&
.SHORT TERM /TODAY THROUGH WEDNESDAY/...
The latest forecast remains on track this morning with no
updates. Light flow in the lower levels combined with the
longer nights and low level moisture has allowed for areas of
low clouds and fog. Tops near or below 1000 feet with a late
morning/midday breakout. Weak system moving by to the north
spreading middle and high level clouds over the area this
afternoon for partly sunny/mostly cloudy skies. Highs remaining
a little below normal, in the 60s and lower 70s.
Southwesterly flow aloft continuing tonight and Tuesday with an
upper level trough offshore. Increasing low level onshore flow
with a possible convergence zone late tonight into Tuesday
morning over the Central Puget Sound producing some drizzle.
The increase in the onshore flow will limit fog coverage late
tonight but with plenty of low level moisture will still have
low clouds developing in the overnight hours. Low clouds
dissipating midday Tuesday with mostly sunny skies in the
afternoon. Lows in the upper 40s to mid 50s. Highs in the 60s.
Next system spinning out of the upper level trough offshore
falling apart as it reaches the coast early Wednesday morning.
What is left of the system moving through the Northwest
Interior later in the morning for a slight chance of showers. A
couple hundredths along the north coast will be the best this
system can do rain wise. Middle and high level clouds with the
system will make for a partly sunny/mostly cloudy day for the
interior. Lows in the mid 40s to lower 50s. Highs in the 60s.
Felton
&&
.LONG TERM /WEDNESDAY NIGHT THROUGH SUNDAY/...
Models in good agreement with a consolidated front reaching the
area late Thursday night/Friday morning. Rain out ahead of
the front spreading over the area Thursday afternoon into
Thursday evening. This system will have a little juice with it
with a half to one inch of rain along the coast, Olympics and
Central and Southern Cascades and a quarter to half inch over
the interior. Right now the North Cascades looks to be the
wettest location with one to one and a half inches of water.
Snow levels lowering to 6000 to 6500 feet giving the higher
elevations a few inches of snow. Upper level trough behind the
front showing signs of digging south and becoming slightly
negatively tilted Friday morning which could stall the system
over the area into Friday afternoon. Upper level trough moving
through Friday evening. Cool days Thursday and Friday with highs
only in the lower to mid 60s. Lows in the mid 40s to lower 50s.
Models continue to be in good agreement over the weekend with a
flat upper level ridge over the area. Warm front dissipates
before it reaches the coast Sunday. Post frontal onshore flow
and the lack of much ridge building will keep temperatures cool.
Highs remaining in the lower to mid 60s. Mornings will be on
the cool side as well with the coldest locations dropping into
the upper 30s. Lows in the 40s for most places.
Just a note the autumnal equinox is at 5:05 pm Tuesday the
22nd.
Felton
&&
.AVIATION...
Southwest flow aloft is expected across Western Washington today as
a dry cold front moves onshore across the region. Low level onshore
will increase behind the front today for increasing low level
moisture across the lowlands later tonight through most of Tuesday
morning. Areas of LIFR/IFR stratus will clear most areas by midday
today as high and mid level moisture spreads overhead. Widespread
MVFR ceilings will develop tonight and persist across the lowlands
into early afternoon on Tuesday.
KSEA...VFR with high and mid level clouds today. MVFR ceilings will
develop overnight tonight and will likely hang around through at
least midday on Tuesday. Surface winds S/SW 7 knots or less will
veer light N/NW for a period this evening before backing once again
to light southerly Tuesday morning.
27
&&
.MARINE...
High pressure will weaken over the coastal waters this morning.
A weak cold front will traverse the area waters this afternoon into
early Tuesday, resulting in increased onshore flow. Winds will
increase this afternoon through the Strait of Juan de Fuca and will
reach Small Craft Advisory thresholds through late tonight. The
advisory was extended slightly to account for the potential of some
lingering gusts into early Tuesday morning.
Another push of westerlies through the Strait of Juan de Fuca is
forecast Tuesday evening, but guidance remains confident in the
strongest winds remaining on the Canadian side of the strait.A
weakening front then moves across the waters on Wednesday, with the
potential for another weather system moving through late Thursday
into Friday.
Seas of 3 to 5 feet will build to 7 to 9 feet tonight as a longer
period northwesterly swell arrives to the coastal waters.
Ensemble guidance has backed off on the probability for seas greater
than 9 ft (15-25% or less). Seas then subside to 6 to 8 feet Tuesday
afternoon and remain like so through the remainder of the week.
62
&&
.SEW WATCHES/WARNINGS/ADVISORIES...
WA...None.
PZ...Small Craft Advisory from 2 PM this afternoon to 3 AM PDT
Tuesday for Central U.S. Waters Strait Of Juan De Fuca-
East Entrance U.S. Waters Strait Of Juan De Fuca.
&&
$$
NWS SEW Office Area Forecast Discussion