421
FXUS66 KSEW 180346
AFDSEW

Area Forecast Discussion
National Weather Service Seattle WA
846 PM PDT Sun Aug 17 2025


.UPDATE...No changes made to this evening`s update. Mid to high
level cloud coverage will maintain tonight. Mostly dry but a
slight chance (15%) of showers may make it to near Neah Bay and
the North Coast by the early morning hours on Monday. A lesser
chance exists of them making it towards the interior. Overnight
lows will bottom out generally in the lower 50s to upper 50s - the
Seattle area will be around 60 F. The previous discussion remains
below along with an updated aviation section:


&&


.SYNOPSIS...Cooler conditions with cloudy skies and periods of
showers along the coast will continue through the middle of the
week as troughing continues offshore. A warmer and drier pattern
will develop later in the week as high pressure builds over the
southwestern US.

&&

.SHORT TERM /TONIGHT THROUGH WEDNESDAY/...A longwave trough off
the Pacific Northwest coast will be the primary weather maker
through the short term, advecting moisture into the region and
maintaining cloud cover and cooler temperatures. As the center of
the low pressure system slowly tracks towards British Columbia,
chances for light rain showers will persist through Tuesday along
the Pacific coast and northern Interior. The system will track
inland to the north on Wednesday, with weaker zonal flow briefly
developing. Onshore flow will promote cloudy skies each day, with
morning stratus advancing eastward in the mornings and breaking up
by the afternoon. Temperatures through Wednesday will remain
fairly steady, in the upper 70s across much of the interior and in
the upper 60s along the coast.

.LONG TERM /THURSDAY THROUGH SUNDAY/...Another cutoff low will
begin to strengthen over the Gulf of Alaska on Thursday, where it
will remain through much of the weekend. High pressure will begin
building over the southwestern US, allowing for dry and sunny
conditions across western Washington with warming temperatures.
Highs will surpass the 80s across much of the interior by Friday,
remaining in the low to mid 80s through the remainder of the
weekend. This will generate Moderate (Orange) HeatRisk across
portions of the area next weekend, and conditions will continue to
be monitored.

15

&&


.AVIATION...Southwest flow aloft will continue through Monday with
upper troughing offshore. VFR conditions this evening with
widespread mid and high clouds across Western Washington. Conditions
are expected to deteriorate along the coast towards LIFR/IFR tonight.
Low clouds are expected to be confined to the coast tonight into
Monday morning. Mid and high clouds will continue for interior
sites, with only a slight chance (less than 10%) of MVFR cigs
developing around Puget Sound early Monday morning. Otherwise, mid
to high clouds will be around Monday afternoon. Light W/NW surface
winds this evening will increase from the S/SW Monday afternoon.

KSEA...VFR conditions will continue through Monday with mid and high
clouds. Generally W/NW surface winds this evening will shift to the
S/SW tonight (mainly after 09z). SW winds will increase Monday
afternoon. JD

&&

.MARINE...High pressure over the waters today will begin to weaken
tonight into Monday. A weak frontal system will dissipate over the
coastal waters Monday night. High pressure will rebuild over area
waters on Tuesday and will strengthen through Thursday. High
pressure will weaken slightly on Friday. Generally benign marine
conditions expected through Friday with waves hovering at 3-5 ft.

29

&&

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

$$