805
FXUS66 KSEW 251017
AFDSEW

Area Forecast Discussion
National Weather Service Seattle WA
317 AM PDT Fri Jul 25 2025

.SYNOPSIS...Upper level trough along with low level onshore flow
will give Western Washington a couple of cool and mostly cloudy
days today and Saturday. Upper level ridge building over the area
beginning Sunday with sunny and warmer weather next week.
Southerly flow aloft developing midweek brings up the possibility
of late day convection over the Cascades Wednesday and Thursday.

&&

.SHORT TERM /TODAY THROUGH SUNDAY/...Satellite imagery shows
stratus along the coast, Southwest Interior and Kitsap Peninsula
into the Central Puget Sound at 10z/3am. Stratus also spreading
over the Northwest Interior. Temperatures were in the 50s.

Upper level trough developing today with the trough axis
offshore. Low level onshore flow throughout the day. While the
interior onshore gradients weaken, the cross Cascade gradient
increases with KSEA-KEAT and KSEA-KYKM possibly as high as plus 10
mb by 00z this afternoon. This will keep reinforcing the marine
layer while the July sun tries to erode it. In the end the onshore
flow will win the battle most of the day with cloudy skies only
giving way to partly sunny conditions in the afternoon. The
prolonged cloud cover will keep high temperatures in the 60s to
lower 70s, well below normal for this time of year ( Seattle
normal is 79 degrees ).

Little change in the pattern tonight and Saturday. Weak upper
level trofiness remaining over the area with the trough axis
offshore. Low level onshore flow a little weaker Saturday for a
slightly earlier appearance of the sunshine in the afternoon.
Highs a little warmer for the interior, mid 60s to mid 70s. Highs
on the coast will remain in the lower to mid 60s. Lows tonight in
the 50s.

Slight change in the pattern later Saturday night into Sunday.
Upper level trough centered offshore begins to weaken while the
huge upper level ridge over the middle of the country starts to
slowly back build towards the Pacific Northwest. Onshore flow
continues to weaken Sunday with 500 mb heights up to the upper 570
dms by 00z Monday. Sunday will continue the trend of a little
more sunshine in the afternoon and a little bit warmer
temperatures. Highs mostly in the lower to mid 70s for the
interior and mid 60s coast. Lows Sunday morning in the 50s.

.LONG TERM /MONDAY THROUGH THURSDAY/...Extended models in good
agreement with the upper level ridge continuing to build over
Western Washington Monday and Tuesday, 500 mb heights in the mid
580 dm with just light onshore flow. Highs warming to normal
Monday, 70s and lower 80s for the interior and a little above
normal Tuesday, mid 70s to mid 80s for the interior. The coast
will stay in the 60s Monday but could see some lower 70s Tuesday.

Model solutions become more diverse Wednesday and Thursday with
the introduction of a weak upper level low off the California
coast. Some model solutions have the remnants of the low near
Western Washington Thursday. Other solutions keep this feature
south of the area before it dissipates. Models have trouble with
this kind of feature this time of year. Pattern recognition
southerly flow aloft, which the low could produce over the area,
means the potential for convection over the mountains in the
middle of summer. MUCAPE clusters are consistent with 500-1000
J/KG Wednesday afternoon over the Olympics and the Cascades
indicating the models are picking up on some instability. Way too
far out at this point for specifics. For now just a slight chance
of showers both days in the Cascades. Given the very dry
conditions over the area any potential for convection is very
closely monitored. Temperatures remaining near to a little above
normal both days. Felton

&&

.AVIATION...A shallow trough north in British Columbia will slowly
dig southward today. Weak zonal flow aloft will increase and turn
slightly west-southwest as this feature digs down. With the
increased onshore flow associated with the trough, the marine
stratus has made an earnest push into Puget Sound earlier this
morning, as it now extends into Snohomish county and will continue
to progress inland. Cigs within the marine layer have been MVFR to
IFR. Given the increased extent, the stratus may linger a bit longer
than the previous few days, with an anticipated scattering time
closer to 18Z-20Z today. Thereafter, expect a VFR afternoon and
generally southwesterly winds. Conditions will be breezy again
through the Strait of Juan de Fuca tonight.

KSEA...Conditions have deteriorated as the marine stratus has made a
rapid advance this morning. IFR cigs at the terminal at 009 to 012
with continued southwesterly surface flow. Expect IFR cigs through
16Z-17Z, improving to MVFR and then VFR between 20Z-21Z. Winds are
expected to be southwesterly through much of the TAF period, but a
period of northerly winds is possible after 00Z, becoming light and
variable after 07Z. While northerly, the wind speeds will be between
5-7 kts.

21

&&

.MARINE...An upper level trough will bring increasing onshore flow
today. Marine stratus has made it inland to Puget Sound and locally
lower visibilities over the waters is possible through much of the
morning. Another westerly push through the Strait of Juan de Fuca is
forecast for this evening, but will be more likely of Small Craft
Advisory magnitude and not Gales. The gustiest portion of the Strait
to be impacted will be the Central Strait, but a SCA has been posted
for the eastern and central Strait. Coastal seas will remain 5 feet
or less throughout the weekend.

21

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...None.
PZ...Gale Warning until 5 AM PDT early this morning for Central U.S.
     Waters Strait Of Juan De Fuca-East Entrance U.S. Waters
     Strait Of Juan De Fuca.

     Small Craft Advisory from 5 PM this afternoon to 2 AM PDT
     Saturday for Central U.S. Waters Strait Of Juan De Fuca-
     East Entrance U.S. Waters Strait Of Juan De Fuca.

&&

$$