158
FXUS66 KSEW 090937
AFDSEW

Area Forecast Discussion
National Weather Service Seattle WA
237 AM PDT Wed Jul 9 2025

.SYNOPSIS...A weak front will slide across western Washington
today, bringing in light rain alongside cooler temperatures and
locally breezy winds. High pressure will rebound by Friday,
bringing a warming and drying trend through the weekend and into
early next week.

&&

.SHORT TERM /TODAY THROUGH FRIDAY/...An approaching weak cold
front will bring a considerable cool down to western Washington
today as a strong push of marine air moves into the region. A band
of light rain showers and virga will continue to shift southward
throughout the morning and into the early afternoon, bringing
light precipitation and locally breezy winds up to 25-30 mph. The
bulk of the moisture with this system will be focused over the
North Cascades, where generally up to a half inch of rain is
forecast, with locally higher amounts closer to an inch over the
higher peaks. Elsewhere, areas along the coast and lowlands north
of Everett will see up to a quarter of an inch of rain throughout
the day, and rain shadowing will cause areas around the Puget
Sound to see little to no rain accumulation. A convergence zone
will develop later this afternoon between Seattle and Everett,
with additional rainfall accumulations of a tenth of an inch over
the Central Cascades and Foothills. The incoming moist marine air
will cool temperatures considerably, with highs today peaking in
the mid to upper 60s to low 70s for most lowland areas.

Onshore flow will persist into Thursday morning, and an additional
round of incoming moisture may bring a drizzle to some areas
early Thursday morning while much of the region will see little
more than cloudy skies lingering into the morning hours. Skies
will clear by Thursday afternoon, with temperatures returning to
near normal in the low to mid 70s across the lowlands.

High pressure will continue to build into western Washington on
Friday, allowing for a warming and drying trend. Temperatures will
rebound back into the 80s for much of the interior and into the
70s along the coast. This will result in widespread Minor (yellow)
HeatRisk, with pockets of Moderate (orange) HeatRisk through the
Olympia and Tacoma metro areas south of the Puget Sound.

.LONG TERM /SATURDAY THROUGH TUESDAY/...Ensembles continue to show
good agreement over high pressure building offshore through the
weekend and into early next week, allowing for warmer and dry
conditions across western Washington. This will give another
potential period of increased HeatRisk as well as an increase in
fire weather concerns over the weekend and into early next week.
However, onshore flow will keep temperatures slightly moderated
through the weekend while providing decent overnight humidity
recoveries. Forecast models amplify the high pressure offshore on
Tuesday, allowing temperatures to climb well above normal with
highs peaking in the upper 80s across the lowlands. This may
bring widespread Moderate (orange) HeatRisk to the region,
especially if winds shift eastward as offshore flow develops.

15

&&

.AVIATION...A weak shortwave trough today will swing a weak cold
front through western WA today (the flow aloft will change from
southwesterly to northwesterly). VFR conditions continue as of 09Z
over much of the interior terminals. Low clouds have begun to fill
inland however (IFR/LIFR ceilings currently along the coast, with
IFR also being reported at KSHN and KNUW - some lower visibilities
also present along the coast due to mist/fog). The front has slowed
a bit from the previous discussion - still expect for interior
terminals to lower to MVFR between 09-12Z this morning (satellite
does show increasing ceilings beginning to fill in from the
southwest into Puget Sound, and to the north of KPAE). IFR/LIFR is
expected to remain out of the major Puget Sound terminals (but will
become widespread to the west of the sound and also over
Whidbey/Strait of Juan de Fuca areas down to KPAE).

Showers continue in Whatcom County this morning, with additional
showers expected to develop across all remaining terminals late this
morning and afternoon. Additional showers will be possible later
tonight/Thursday morning, as well as a convergence zone continuing
showers over Snohomish/King County through the evening. The ceilings
will lift slightly through the afternoon/evening, however only
isolated areas across the region will see improvement to VFR before
tonight. Additionally, southwest winds will pick up 8-12 kt with
gusts to 20 kt possible late this morning and afternoon - will
become more westerly for most areas tonight and decrease to below 10
kt. Diffluence from a marine push through the Strait of Juan de Fuca
will turn winds northerly through Puget Sound this afternoon -
likely down to KBFI and KSEA after 00Z.

KSEA...MVFR expected to develop (based on satellite trends/model)
between 09-12Z this morning (20% chance this dips down to IFR, but
looks to be lower end MVFR bases as of writing with bases). The
ceilings will improve to above 2,000 feet this evening (but remain
below 3,000 feet). Showers will be possible after 12Z this morning,
and may remain in the vicinity of the terminal through the evening
(via a convergence zone) before the next round of showers arrives
later tonight. Breezy southwest winds 8-12 kt gusts to 20 kt will
develop this morning, but decrease to below 10 kt as diffluence from
a marine push turns the winds northeasterly after 00Z.

HPR

&&

.MARINE...A weak cold front and associated trough will push through
the waters today. Satellite has shown some patchy fog over the
coastal waters late last night into the morning. Given the patchy
nature of the fog (based on satellite and observations), opted to
issue a marine weather statement for the coastal waters/Grays Harbor
areas through 18Z. Showers will pick up late this morning into the
afternoon across the coastal waters (spreading inland across
interior waters not covered from this morning`s showers in the far
Northern Inland Waters). Winds will pick up out of the southwest
today ahead of the front, but the only areas expected to see winds
hazardous for small craft are the central/east sections of the
Strait of Juan de Fuca (issued a new SCA from this afternoon through
Thursday morning). A couple spots in Puget Sound may also see a
couple gusts to 20 kt.

Post front, heights will build offshore with high pressure remaining
dominant through the weekend into next week. The flow over the
coastal waters will turn northerly as a result. Some fog/low stratus
will be possible again Thursday morning.

Seas will increase from 2 to 4 to 6 to 8 feet this weekend, with the
seas this weekend potentially becoming steep (with shorter periods).

HPR

&&

.FIRE WEATHER...A weak frontal system will move through the region
today, with elevated onshore flow bringing in cooler and more
moist conditions with some light precipitation. Wetting rains are
possible across portions of the Northern Cascades and Pacific
Coast.

Upper ridging will then build back into Western Washington late
Thursday, resulting in the return of warm, dry weather and elevated
fire weather conditions on Friday. This will be the driest day of
the period, with RH values dropping back into the 25% to 35% range
over the mountains and across the lowlands south of the Puget Sound.
Warm and dry conditions look to persist into next week but the
details remain uncertain at this point to the degree of onshore flow
going into next week.

Conditions will warm up significantly by the middle of next week,
with forecast models hinting at a shift to offshore flow and east
winds through the Cascade gaps. These conditions will continue to
be closely monitored.

15

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...None.
PZ...Small Craft Advisory from 2 PM this afternoon to 5 AM PDT
     Thursday for Central U.S. Waters Strait Of Juan De Fuca-
     East Entrance U.S. Waters Strait Of Juan De Fuca.

&&

$$