680
FXUS66 KSEW 220347
AFDSEW

Area Forecast Discussion
National Weather Service Seattle WA
847 PM PDT Mon Jul 21 2025

.SYNOPSIS...An upper trough will move eastward into Tuesday.
Brief high pressure returns around midweek for warmer and drier
conditions before a weak disturbance drops across the region
late in the week.

&&

.SHORT TERM /TONIGHT THROUGH WEDNESDAY NIGHT/...An area of
lingering light rain continues to dissipate this evening across
Skagit and Snohomish Counties. This batch of rain will continue
to taper off over the next few hours. Otherwise, a few showers
or even localized thunderstorms may be around into tonight north
of Snohomish County and into the Cascades as convection slides
southwards from BC. No other major forecast updates this
evening.

Expect another round of marine stratus to push onshore with a
few areas of denser fog possible by daybreak along the coastline
and pushing into Whidbey Island through the Strait. The threat
for thunderstorm diminishes dramatically on Tuesday, but a few
lingering showers may develop in the afternoon near the Cascades
again.

Weak high pressure begins to build late Tuesday and builds more
significantly into Wednesday. While the ensemble guidance still
has some decent spread with respect to how warm the air mass
will be, there is decent agreement suggesting temperatures
returning back into 80s for afternoon highs. While most of the
area will remain in Minor (Yellow/level 1 of 4) HeatRisk on
Wednesday, it`s expected that the greater Seattle/Tacoma metro
area could again reach Moderate (Orange/level 2 of 4) HeatRisk.
This will, however, be a brief warm-up across the region which
should limit heat impacts from becoming more severe.

&&

.LONG TERM /THURSDAY THROUGH MONDAY/...Another disturbance will
beginning to move into the region late in the week, enhancing
onshore flow and spreading more cloud cover into the region.
This will see temperatures returning to near seasonal normals
late in the week. Lower confidence in the pattern with the
ensemble guidance struggling with the upper low that cuts off
off the California coast, but confidence is higher today that
this will remain far enough from the local area to not disrupt
the mostly zonal flow. This will keep the region in a pattern of
morning clouds and mild, sunny afternoons, with temperatures
gradually warming through the weekend into the start of next
week. Cullen

&&

.AVIATION...Northerly flow aloft through Tuesday as W WA finds
itself on the backside of an exiting upper level trough. Surface
winds largely south to southwest 5-10 kts with the exception of CLM
where westerly push down the Strait is dictating direction.

Majority of terminals remain VFR this early evening although seeing
mid to high level clouds spilling westward from thunderstorm
activity over the Cascades. This is not expected to have a
significant impact on flight conditions for the Puget Sound area
terminals. IFR conditions already in place over coastal areas due to
persistent stratus. Marine push overnight will allow these stratus
to become more widespread over W WA, resulting in MVFR to IFR
conditions for all terminals within a 10-14Z window and persisting
into late Tuesday morning. Cigs expected to erode with VFR
conditions returning around 18Z, except for HQM...who will likely
see some improvement, but remain MVFR at best for the TAF period.

KSEA...VFR into tonight with mid to high level clouds from
showers/thunderstorms over the Cascades. Onshore flow will
strengthen Tuesday morning, with IFR or low end MVFR stratus favored
(30% to 40% probability) to drift over the terminal by sunrise and
burn off by 18Z Tuesday. Surface winds generally SW 4 to 9 kt
through the period.

18/15

&&

.MARINE...Broad surface ridging centered well offshore and lower
pressure east of the Cascades will remain in place into midweek with
diurnally driven increases in onshore flow. This will result in
several westerly pushes through the Strait of Juan de Fuca, with
winds already reaching SCA speeds this evening and potentially again
Tuesday evening. Another upper level trough moving into British
Columbia late in the week will increase the onshore flow for
possible westerly gales in the Strait Thursday into Friday.

Seas will remain benign through the period, generally staying
between 3 to 5 feet.

15/18

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...None.
PZ...Small Craft Advisory until 3 AM PDT Tuesday for Central U.S.
     Waters Strait Of Juan De Fuca-East Entrance U.S. Waters
     Strait Of Juan De Fuca.

&&

$$