045
FXUS66 KSEW 172231
AFDSEW

Area Forecast Discussion
National Weather Service Seattle WA
331 PM PDT Thu Jul 17 2025

.SYNOPSIS...Gradually cooler conditions develop over the region
as strengthening onshore flow will bring increasing clouds and
cooler conditions. The next upper level disturbance will bring
cooler conditions late in the weekend and a return of shower
chances, especially over the Cascades, early next week. Another
warm up appears likely toward the middle of next week.

&&

.SHORT TERM /TODAY THROUGH SATURDAY NIGHT/...Temperatures
running 7 to 10 degrees cooler through the I-5 corridor compared
to this time yesterday. A weak disturbance will swing through
the region on Friday, bringing stronger onshore flow and
progressively cooler conditions. Expect morning clouds and
cooler conditions, with some clearing Saturday afternoon. This
will bring temperatures back down closer to normal values over
the weekend.

&&

.LONG TERM /SUNDAY THROUGH THURSDAY/...Continued onshore flow,
enhanced as an upper level trough slides toward the region. This
may knock temperatures down to near or just below seasonal
normals on Sunday. Ensemble guidance is in good agreement that
a deeper upper trough will slide down into the Pacific Northwest
on Monday and bring a return of shower chances to portions of
the Cascades, especially north of I-90. This will keep cooler
conditions and additional clouds for the start of the week.
Ensemble guidance remains a bit more split toward midweek, but
there`s an increasing likelihood that a building ridge offshore
will bring another warmer and drier trend toward the middle of
next week.

&&

.AVIATION...VFR ceilings expected to prevail today. However, lower
ceilings will return overnight, with MVFR ceilings along the
interior terminals and IFR/LIFR along the coastal terminals.
Improvement into VFR expected late Friday morning/Friday afternoon,
with the exception of the coast. Rather, conditions will improve to
MVFR along the coast.

N/NW winds today at 4-7 kt, while more westerly winds along the
coast with breezy winds at 8-10 kt. Winds will turn SW overnight and
will become breezy Friday morning around 8-14kt, continuing
throughout the evening. The breeziest spots will be along the
southern interior (KOLM), the coast, and Strait of Juan de Fuca,
where gusts between 15-20 kt are likely (70%-90% chance).

KSEA...VFR conditions today, but MVFR ceilings expected overnight.
Improvement is expected after 18z. NW winds this afternoon 5-7 kt,
turning SW overnight 4-7 kt. Breezy SW winds will ensue Friday
morning and persist throughout the evening, with speeds of 10-12 kt.
The probability of seeing gusts greater than 15 kt are currently
around 40%-50%.

29

&&

.MARINE...Northwesterly surface winds expected to prevail over the
coastal waters. A cold front will descend from Canada on Friday,
bringing elevated winds over the outer coastal waters. In addition,
steep seas with wave heights of 8-9 ft with a dominant period of 9
seconds are expected. Consequently, a Small Craft Advisory has been
issued for the outer coastal waters. Westerly pushes across the
Strait of Juan de Fuca will occur each evening. Tonight`s westerly
push will meet small craft criteria, and an advisory has been
issued. Confidence has also increased that a Small Craft Advisory
will likely be needed Friday evening, as probabilities of seeing
sustained wind speeds of 21 kt or greater is around 70-90%. On
Friday evening, surface high pressure will rebuild over area waters,
weakening on Sunday into early next week.

29

&&

.FIRE WEATHER...Elevated fire weather concerns will remain through
the evening for the Cascades for hot, dry, and unstable conditions.
Onshore flow continues to bring cooler and moist air into the
region. This will reach the Cascades by this evening/Friday morning.
The thermal trough to the east of the Cascades will continue to move
away from the region. Winds will turn northwest today at up to 5-10
mph, and may be gusty up to 20 mph in some south interior areas
Friday. Cool and moist conditions will remain through the weekend,
with temperatures increasing next week. There is a slight chance of
showers and isolated thunderstorms in the north Cascades Monday and
TUesday, which may return elevated fire weather conditions (due to
lightning).

HPR

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...Heat Advisory until 8 PM PDT this evening for City of Seattle-
     Downtown Everett / Marysville Area-Eastside-Foothills and
     Valleys of Central King County-Foothills and Valleys of
     Pierce and Southern King Counties-Foothills and Valleys
     of Snohomish and Northern King Counties-Foothills and
     Valleys of the North Cascades-Lowlands of Pierce and
     Southern King Counties-Lowlands of Western Skagit and
     Northwestern Snohomish Counties-Lowlands of Western
     Whatcom County-Shoreline / Lynnwood / South Everett Area.
PZ...Small Craft Advisory from 6 PM this evening to 5 AM PDT Friday
     for Central U.S. Waters Strait Of Juan De Fuca-East
     Entrance U.S. Waters Strait Of Juan De Fuca.
     Small Craft Advisory from 11 PM this evening to 2 PM PDT
     Friday for Coastal Waters From Cape Flattery To James
     Island 10 To 60 Nm-Coastal Waters From James Island To
     Point Grenville 10 To 60 Nm-Coastal Waters From Point
     Grenville To Cape Shoalwater 10 To 60 Nm.

&&

$$