627
FXUS66 KSEW 170935
AFDSEW

Area Forecast Discussion
National Weather Service Seattle WA
235 AM PDT Tue Sep 17 2024

.SYNOPSIS...A upper level trough and associated front will push
through the region late Tuesday for some rain showers into
Wednesday. Drier conditions into Thursday before unsettled weather
likely returns to the area through the weekend.

&&

.SHORT TERM /TODAY THROUGH THURSDAY/...The forecast leans toward
cooler conditions through Wednesday with troughing over the Pac
NW. High temperatures will track in the 60s or a few degrees
cooler than average. Expect lows in the 40s and 50s. Rain moves
into the coast this afternoon with a few light showers reaching
the interior as well. Look for drier conditions this evening as
this system pushes south. May see light rain or drizzle in the
central sound Wednesday morning where there`s convergence. Weak
ridging nudges inland on Thursday for drier and slightly warmer
weather. 33

.LONG TERM /FRIDAY THROUGH MONDAY/...Onshore flow prevails into
the weekend as the flow aloft turns zonal. This opens the door as
wetter Pacific systems roll in, with most of the ensemble members
showing measurable rain. Skies remain mostly cloudy throughout
with the onshore conditions and moist low level air mass. With
this, temperatures will continue to trend cooler than average.
There`s little overall change in the pattern moving into early
next week for more fall-like weather. 33

&&

.AVIATION...West to southwest flow aloft will become east/northeasterly
tonight as an upper level trough moving into the offshore waters
shifts southward. A marine layer spreading inland will lead to
widespread IFR or lower MVFR ceilings across the lowlands of
Western Washington this morning. Moisture will deepen with the
arrival of the trough and MVFR ceilings are expected to linger
through the day. Areas of light rain are expected to develop
midday mainly west of Puget Sound.

KSEA...Marine layer will arrive before daybreak with IFR ceilings.
These will lift to MVFR later this morning then persist through the
day. Surface winds southerly rising to 7 to 10 knots by late
morning. 27

&&

.MARINE...A weak surface low will shift southward over the offshore
waters today into tonight, but is not expected to produce any
headlines. Broad surface ridging centered well offshore rebounds
Thursday into Friday. Northwesterlies may approach small craft
advisory levels late this week across the outer coastal waters,
otherwise fairly tranquil conditions are expected into early
Saturday. Forecast confidence is low by early next week, but model
ensembles suggest about a 20 to 30 percent probability of small
advisory level winds for portions of the coastal waters with a
frontal system on Sunday. 27

&&

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

$$