Brier Weather Station
Latitude N 47° 46' 49" Longitude W 122° 16' 48" Elevation 341 ft
839
FXUS66 KSEW 281025
AFDSEW
Area Forecast Discussion
National Weather Service Seattle WA
325 AM PDT Mon Sep 28 2026
.SYNOPSIS...Surface high pressure weakening today. Zonal flow
aloft. Next system moving down British Columbia coast moving
through the area Tuesday. Post frontal convergence zone Tuesday
evening. High pressure, both surface and aloft, rebuilding
Wednesday. Upper level ridge remaining over the area through the
weekend. Thermally induced surface trough moving up the Oregon
coast reaching the Washington coast Saturday turning the low
level flow offshore. Surface trough moving inland Sunday.
&&
.SHORT TERM /TODAY THROUGH WEDNESDAY/...
Satellite imagery shows high clouds along the coast and over the
Northwest Interior early this morning. Patchy fog forming in the
Southwest Interior with visibility at Chehalis down to a half
mile. Temperatures at 3 am/10Z were in the upper 30s and 40s.
Next system to move into Western Washington currently near Haida
Gwaii and slowly moving southeast. High clouds out ahead of the
system will spread over the remainder of the area this morning
into the afternoon hours. Chance of rain by late afternoon along
the north coast. Highs in the 60s.
Front continuing to slowly move southeast tonight. By 12z
Tuesday front still north of the area. Surface pressure
gradients tightening up over the Northwest Interior as the front
approaches. Have issued a wind advisory for the Northwest
Interior and the San Juans beginning at 2 am Tuesday morning for
southeast winds increasing to 20 to 30 mph with gusts 40 to 45
mph. Rain out ahead of the front reaching the north coast and
Northwest Interior by midnight. Chance of rain as far south as
Olympia by early Tuesday morning. With the cloud cover lows will
be much warmer than the previous mornings, in the lower to mid
50s.
Front slowly moving through Western Washington Tuesday. Rain
over most of the area by mid morning. Front moving through the
Northwest Interior and north coast early afternoon. Winds
easing behind the front. Highs in the lower to mid 60s.
Front moving through the remainder of the area by early in the
evening with rain coming to an end. Post frontal convergence
zone over Snohomish county will dissipate after midnight. Not
much in the way of cool air behind the front with just limited
shower activity outside the convergence zone. Lows in the mid
40s to lower 50s.
High pressure, both surface and aloft, building over Western
Washington Wednesday. Winds easing overnight. Patchy fog
developing early in the morning. What little fog that does form
will be gone by mid morning. Skies clearing with plenty of
sunshine especially in the afternoon. Highs in the lower to mid
60s. Felton
&&
.LONG TERM /WEDNESDAY NIGHT THROUGH SUNDAY/...
Extended models have finally gotten rid of the slight chance
pops for Thursday and Friday. Upper level ridge over the area
with high pressure at the surface. Thermally induced surface
trough moving up the Oregon coast Friday extending north to the
Washington coast Saturday. Low level flow turning offshore. In
this scenario this time of year it is not uncommon for the coast
to be the warmest location in Western Washington. Thermally
induced surface trough moving inland Sunday making it the
warmest day for the interior. Lows in the 40s Thursday morning,
mid 40s to lower 50s Friday through Sunday morning. Highs in the
mid to upper 60s Thursday and Friday, 60s and lower 70s
Saturday and Sunday.
Even with the normal high in Seattle starting October at 66
degrees, the normal number of 70 degree plus in Seattle in
October is only 2. Out of the 170 days total ( in 81 years of
records ), 51 ( 30 percent ) are 75 degrees or warmer. 75
percent of the 70 degree plus days in October have occurred in
the first 10 days of the month and all of the 75 degree plus
days have occurred in the first 16 days of the month. Felton
&&
.AVIATION...
Zonal flow aloft with occasional shifts to the NW at times today,
strengthening tonight as gradients tighten. Light and variable
surface winds this morning becoming southerly 5-10 kt this afternoon
in advance of approaching front. Speeds increase further this
evening and overnight generally ranging 10-15 kt with gusts up to 20
kt possible.
Widespread VFR conditions in place this early morning with isolated
patches of MVFR to IFR conditions due to lingering low-level
moisture. Cigs expected to lower throughout the day as incoming
front approaches, however VFR expected to persist for the majority
of the TAF period for most terminals. Western-most terminals will
begin to encroach on MVFR conditions this evening between 03-06Z
while remaining terminals likely will not see these conditions
emerge until around 12Z Tuesday. Similarly, inclusion of precip will
likely be needed for 12Z issuance for western terminals while
eastern ones likely hold off until 12Z or just a little after, thus
falling outside current forecast window.
KSEA...VFR conditions for nearly the entire period even though cigs
will gradually fall throughout the day. MVFR conditions expected to
develop near the end of the TAF period, around 10-12Z, as front
draws nearer. Start of precip also expected during this time frame.
Light and variable winds this morning before turning more southerly
at 5-10 kt this afternoon. SW winds 10-15 kt with gusts up to 20 kt
after 03Z tonight with best chances for gusts holding off until
the 10-12Z time frame.
18
&&
.MARINE...
The next frontal system arrives Tuesday with increasing southerly
winds over all waters - Small Craft Advisories are in effect
for most waters, although it appears the Northern Inland Waters
run a good chance for consistent gusts exceeding Gale criteria.
As such, have upgraded the SCA there to a Gale Warning. Winds
will turn more westerly through the Strait Tuesday afternoon.
Meanwhile, expect elevated seas with swells reaching 10-11 ft.
Onshore flow will ease late Tuesday night. The flow will then
turn offshore on Wednesday with a thermal trough along the
coast. Light offshore flow continues through the end of the
week. 18/33
&&
&&
.SEW WATCHES/WARNINGS/ADVISORIES...
WA...Wind Advisory from 2 AM to 2 PM PDT Tuesday for Lowlands of
Western Whatcom County-San Juan County.
PZ...Small Craft Advisory from 5 PM this afternoon to 5 PM PDT
Tuesday for Admiralty Inlet-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-Puget Sound and Hood Canal-West
Entrance U.S. Waters Strait Of Juan De Fuca.
Small Craft Advisory from 5 PM this afternoon to 5 AM PDT
Wednesday for Central U.S. Waters Strait Of Juan De Fuca-
East Entrance U.S. Waters Strait Of Juan De Fuca.
Gale Warning from 11 PM this evening to 5 PM PDT Tuesday for
Northern Inland Waters Including The San Juan Islands.
&&
$$
NWS SEW Office Area Forecast Discussion