829
FXUS66 KSEW 201005
AFDSEW

Area Forecast Discussion
National Weather Service Seattle WA
305 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.
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

&&

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

Stratus with IFR ceilings along the central and south coast
getting as far east as the Lower Chehalis Valley this morning
before dissipating 15z-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. 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

&&

.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.
&&

$$