195
FXUS66 KSEW 201546
AFDSEW

Area Forecast Discussion
National Weather Service Seattle WA
846 AM PDT Thu Jun 20 2024

.SYNOPSIS...A upper level ridge offshore will continue to build
into the region through Friday. The ridge will shift east of the
area on Saturday. An upper level trough moving into British
Columbia on Sunday will produce cloudier and cooler conditions along
with a chance of showers. Weak upper level ridging will bring a
modest warming trend and generally dry conditions for much of the
area early next week.

&&

.SHORT TERM /TODAY THROUGH SATURDAY/...Mostly clear skies prevail
across Western Washington early this morning with the exception of
some patchy stratus along the central coast. Gradually rising
heights and light northerly flow near the surface will translate
to 2 to 4 degrees of warming for most of the region...which puts
most of the interior from Seattle southward into the 80s today.
Minimum RH will dip down in to the low 30s to mid 20s through the
Southwest Interior. Weak troughing aloft will probably produce a
few cumulus buildups near the North Cascade crest this afternoon,
but any thunderstorm potential is likely to remain east of the
crest.

Heights continue to rise into Friday for a little additional
warming across interior areas, but increasing low level onshore
flow late in the day should cool coastal areas a few degrees.
The upper ridge axis shifts east of the area Friday night.
Temperatures will cool a few degrees on Saturday as an upper
level trough approaches, but interior locations should squeeze out
one more seasonably warm day. Onshore flow ramps significantly
Saturday night with a likely deepening marine layer and some
drizzle or light showers developing along the coast.

.LONG TERM /SUNDAY THROUGH WEDNESDAY/...An upper level trough is
expected to more onshore over southern British Columbia on Sunday.
This will bring us clouds and significant cooling along with a
few showers...especially coast, mountains, and within a
convergence zone over Snohomish County. The trough washes out
fairly quickly as it pushes eastward on Sunday. Recent model
ensembles as well as deterministic runs are now trending a little
warmer and drier for the early part of the coming week. This is
likely due to some subtle changes in the synoptic pattern as upper
ridging broadens its influence over the western U.S. in response
to the eventual demise of a strong ridge downstream over the
northeastern U.S.

27/LH

&&

.AVIATION...Weak upper level trough over Western Washington this
morning will shift east this afternoon into tonight. Light
westerly flow aloft becoming northwesterly this afternoon. In the
lower levels light onshore flow into Friday.

IFR stratus along the central and south coast getting as far east
as the Lower Chehalis Valley this morning before dissipating
around 18z. Clear skies for the remainder of the area. Low clouds
with IFR ceilings reforming along the central and south coast
after 06z tonight.

KSEA...Clear skies through the TAF period. Northeast wind 6 to 10
knots becoming northwesterly 8 to 12 knots around 21z. Winds
shifting back to northeasterly 6 to 10 knots after 05z.

Felton/Maz

&&

.MARINE...High pressure over the coastal waters with lower
pressure inland through Friday. Onshore gradients increasing
Friday night as weak system approaches the area. Gales possible in
the Central and Eastern Strait of Juan de Fuca with possible small
craft advisory winds in the adjacent waters. System moving
through Saturday with increasing onshore flow behind the system
Saturday night. Gales likely in the Central and Eastern Strait of
Juan de Fuca with small craft advisory winds in the adjacent
waters. Weak surface high pressure over the coastal waters Sunday
through Monday night with onshore flow weakening into the first
part of next week.

Felton

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...None.
PZ...None.
&&

$$