737
FXUS66 KSEW 211604
AFDSEW

Area Forecast Discussion
National Weather Service Seattle WA
904 AM PDT Fri Jun 21 2024

.SYNOPSIS...A upper level ridge over the region today will shift
eastward 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 into the
middle of the coming week before another trough arrives for cooler
conditions and the return of a chance of showers.

&&

.UPDATE...Mostly clear skies across the region except for the
immediate coast where some low marine stratus will erode through
the morning. Highs today will reach into the upper 70s to upper
80s across the lowlands. While the predominant HeatRisk values are
in the minor/yellow category, there is a decent portion of the
urban area that will see moderate/orange HeatRisk levels.
Fortunately this heat will be short lived as onshore flow
increases this weekend and brings some natural A/C. At this time
there are no heat alerts in effect, but it is possible that some
heat-sensitive populations could experience affects from the heat.
-Wolcott-

&&

.SHORT TERM /TODAY THROUGH SUNDAY/...Much like this time
yesterday, mostly clear skies prevail across Western Washington
early this morning except for some patchy stratus along the
immediate coast. An upper ridge axis will slide eastward across
the area later today. 850 millibar temperatures peaking near 14C
today suggest a degree or two of warming for most of the interior
over yesterday while an increasing sea breeze will hold coastal
temperatures near or a little below yesterday`s readings.

Increasing low level onshore flow will pull the marine layer into
the coast and locally inland tonight. Coastal areas will likely
remain socked in with stratus on Saturday, but another day of
sunshine is expected for the interior. Falling heights and a
seepage of marine air inland will cool temperatures a few degrees
on Saturday. The onshore flow really ramps up Saturday night into
early Sunday as an upper trough moves onshore over British
Columbia. Coastal areas should see some drizzle or light showers
Saturday night before the shower threat spreads inland by Sunday
morning. QPF remains minimal, but an expected convergence zone
should squeeze out a few hundredths of an inch over parts of
Snohomish County on Sunday morning. With all of the clouds and
spotty precip, high temperatures over the interior lowlands on
Sunday will be 10 to 15 degrees cooler than Saturday.

.LONG TERM /MONDAY THROUGH THURSDAY/...Just as in previous model
runs, the upper trough washes out fairly quickly as it pushes
inland early Monday with upper ridging quickly rebuilding across
the area. After some morning clouds on Monday, some sunshine is
likely to return with high temperatures bouncing back to near
seasonal levels. The upper ridge is expected to strengthen as the
axis shifts east of the region on Tuesday. This should allow for
some further warming. Another upper trough approaching Vancouver
Island will begin to assert some influence over Western Washington
Wednesday into Thursday with cooling temperatures and a returning
chance of some showers. 27

&&

.AVIATION...High pressure remains in place over the region, moving
east through Saturday. Continued westerly flow aloft with light flow
in the lower levels becoming onshore tonight into Saturday. This
will maintain mostly clear skies area wide, but low stratus and fog
will remain along the coast through 17z. Expect a return of coastal
stratus to the coast after sunset and again a weak push into the
lower Chehalis but unlikely to make it to KSHN/KOLM tonight.

KSEA...VFR conditions continue under clear skies through the period.
Expect north surface winds increasing to 6-8 kt this afternoon.
Surface winds becoming southerly after 12z tonight.

&&

.MARINE...High pressure over the coastal waters with lower
pressure inland today. Onshore gradients increasing tonight as
weak system approaches the area. System moving through Saturday
with increasing onshore flow behind the system Saturday night.
Weak surface high pressure over the coastal waters Sunday through
Tuesday.

Small craft advisory winds in the Central and Eastern Strait of
Juan de Fuca tonight. Gales possible in the Central and Eastern
Strait Saturday evening with small craft advisory winds in
Admiralty Inlet. Felton

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...None.
PZ...Small Craft Advisory from 5 PM this afternoon to 5 AM PDT
     Saturday for Central U.S. Waters Strait Of Juan De Fuca-
     East Entrance U.S. Waters Strait Of Juan De Fuca.

     Gale Watch from Saturday evening through late Saturday night for
     Central U.S. Waters Strait Of Juan De Fuca-East Entrance
     U.S. Waters Strait Of Juan De Fuca.

&&

$$