156
FXUS66 KSEW 172209
AFDSEW

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

.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...VFR conditions area-wide this afternoon and expected to
prevail the rest of today with mostly mid to high clouds over the
region. Conditions expected to deteriorate to IFR/LIFR along the
coast with low clouds moving into the terminal. Latest guidance
suggests the low clouds will be confined along the coast; however
may move inland towards the Kitsap Peninsula. Latest probabilities
are around 20-30% of seeing MVFR ceilings. Improvement into VFR
along the coast expected after 18z-19z. Otherwise, VFR conditions on
Monday. Generally northwesterly flow this evening that will become
southwesterly Monday morning, with speeds of 6-10 kt.

KSEA...VFR conditions will prevail the rest of today and Monday.
Very low chance of seeing MVFR ceilings (less than 10%). Southwest
winds this afternoon veering west-northwesterly at 3-5 kt this
evening after 01z. Winds shift back to southwesterly overnight after
09z and  will increase to 6-8 kt after 16z.

29

&&

.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.

&&

$$