194
FXUS66 KSEW 311004
AFDSEW

Area Forecast Discussion
National Weather Service Seattle WA
235 AM PDT Sun Aug 31 2025

.SYNOPSIS...An upper level low off the coast will keep temperatures
seasonable again today, with slight chances for showers and possibly
an isolated thunderstorm or two over the North Cascades this
evening. Upper level ridging returns Monday, bringing another round
of hot and dry conditions with well above normal temperatures are
expected by mid-week.

&&

.SHORT TERM /TODAY THROUGH TUESDAY/...Latest satellite imagery
showing some scattered mid clouds moving northward over W WA this
early morning. Out west over the Pacific, the center of circulation
for the parent upper level low is fairly apparent. This feature once
again is expected to keep temps more seasonable, akin to yesterday
but maybe a degree or two warmer.

Models have latched back on to the potential for some scattered
showers starting in the late morning and the risk stretching into
the early evening hours. The area with the best chances /and even
those are just 10-20 pct, so not terribly convincing/ seems to be
over the northern half of the Olympic Peninsula and from Everett
northward. They also re-introduce isolated thunderstorms into the
mix but this too is limited to the Cascades of Whatcom, Skagit and
Snohomish counties. Given the back and forth in the models, not too
much confidence in this activity developing, but at the same time
both CAPE and LIs from latest runs certainly indicate that the
potential is there...as such, feel this isolated/slight chance
wording is likely the best fit for the non-zero chance that likely
exists.

The retreat of the upper low back to the Pacific waters and the
building of upper level ridging starting on Monday remains
consistent...so while temps will rise on Monday by a few degrees,
the more noticeable heating will be Tuesday as highs in the interior
start to return to the lower to mid 80s. Locations closer to water
and coastal areas will still linger in the 70s.

18

.LONG TERM /WEDNESDAY THROUGH SATURDAY/...The ridge will remain the
dominant weather feature for much of the long term, however, models
are starting to advertise some mitigating features that could start
to rein in temperatures by the end of the week. This is going to
depend largely on the track of the upper low that retreated from the
area as stated above. Models show a fairly uniform northerly trek
for the system and as it moves, it could bring in a couple of
shortwave disturbances with the first being early Thursday morning.
While this feature is expected to be dry, some strengthening
northerlies/onshore flow will help to actually trigger a cooling
trend in daytime highs. Temps look to peak on Wed, with mid to upper
80s for interior lowlands...maybe as high as 90 for the Cascade
valleys...before falling back into the lower to mid 80s for Thu. A
secondary shortwave nearly 24 hours later will have a similar
effect, bringing temps down further to the upper 70s to around 80.
Saturday raises some interesting questions, as while there is
general agreement on a transition over to a more troughy pattern,
the orientation of the trough will play a big role as to whether or
not W WA could see the return for some chances for precip. No
consensus has emerged at this time, so confidence remains low.
However, this looks to at least keep the cooling trend intact, with
daytime highs a degree or two cooler than Friday.

18

&&

.AVIATION...Southerly flow aloft will increase today as an upper low
offshore drifts towards the coast. Areas of MVFR/IFR stratus will
redevelop early this morning and fill in eastward, though some
uncertainty remains over how far inland the stratus will expand.
Ceilings will then improve this afternoon to VFR. A few showers may
develop this afternoon over the Olympic Peninsula and interior areas
mainly north of KPAE.

KSEA...VFR conditions early this morning with mid and high clouds at
times. The presence of the upper trough offshore complicates the
forecast in terms of low ceiling development this morning. MVFR/IFR
ceilings are possible between 14z-18z, but confidence is low.
Surface winds light northerly shifting W/NW Sunday afternoon.

15

&&

.MARINE...An onshore flow pattern will continue into next week.
Onshore flow will vary in intensity, with westerly pushes through
the Strait of Juan de Fuca each evening. An SCA remains in effect
this evening for the central and eastern Strait of Juan de Fuca.
Onshore flow will then continue into midweek.

Although primarily dry conditions are expected, there is less than a
10% chance of thunderstorms into Sunday as well.

Seas of 2 to 4 feet for the Coastal Waters through Tuesday will
build to 4 to 6 feet by midweek.

15

&&

.FIRE WEATHER...A slight chance of dry thunderstorms is forecast for
the north Cascades this evening thanks to a low pressure system
parked offshore sending a weak impulse into the area. While this
will steepen lapse rates and offering some ascent, it will likely be
weak and perhaps more terrain driven. With no significant source of
moisture, there is some concern over dry lightning strikes, however,
given the poor dynamics and waffling of model runs as to this
prospect, confidence remains low. Any storms that happen to develop
will be capable of gusty and erratic winds as a by-product of the
steep lapse rates and downdraft CAPE, as well as lightning on dry
fuels. The probabilities are capped at 10-15%.

Later this week, temperatures will be climbing and humidity dropping
off, with poor overnight recoveries. Temperatures will be well into
the upper 80s to mid 90s, with near 100 degrees in the Cascade
valleys as periods of light offshore flow develop during the day.
Elevated concerns for hot, dry and unstable conditions will persist
through much of the mid to late week period.

21/18

&&

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

&&

$$