742
FXUS66 KSEW 302153
AFDSEW

Area Forecast Discussion
National Weather Service Seattle WA
253 PM PDT Wed Jul 30 2025

.SYNOPSIS...Southerly flow aloft will continue through Thursday,
allowing for warm temperatures and chances for thunderstorms over
the Cascades this afternoon, and Friday afternoon and evening.
Onshore flow will redevelop over the weekend, with the potential
for additional systems moving through early next week, bringing
slight chances for showers.

&&

.SHORT TERM /TONIGHT THROUGH SATURDAY/...The overall upper level
pattern remains the same today, upper level ridging nosing in from
the southwest with a large closed low in the Gulf of Alaska
maintaining south to southeasterly flow aloft over the area. This
is helping to produce warm, dry, and unstable conditions over
the area. Temperatures this afternoon are in the mid to upper 70s,
except 60s along the coast. Still on track for highs to reach the
80s for much of the interior, with upper 60s to 70s along the
coast and the north interior. Low temperatures tonight in the 50s
to near 60.

A shortwave impulse will move to the north-northeast into the
Pacific Northwest by Thursday afternoon. This will bring the
needed upper level support as well as additional moisture and
instability for widespread thunderstorms across the broader area.
For western Washington, this will culminate with additional
chances for thunderstorms across the Cascades, as well as slightly
more moist air and thus a slower warm-up throughout the day.
Highs will be a few degrees cooler area-wide, in the 70s for the
coast and northern interior up to low to mid 80s across the
interior. The CAMs continue to show somewhat limited coverage of
thunderstorms over the Cascades, but with very slow north-
northwesterly storm motions, that will allow for the potential of
lightning along the western side of the crest of the Cascades.
Additional, high precipitable water anomaly values (0.25-0.35"
above climo) indicate heavy downpours will also be a threat with
these thunderstorms. If any develop over the area burn scars,
flash flooding will be a threat. The thunderstorm threat does
continue into the early overnight hours Thursday night as the vort
max passes near/just east of the area, but by then, the overall
instability should be a bit lower, meaning anything that drift
into the foothills/lowlands should mostly be showers but a few
lightning strikes cannot be ruled out.

Lingering instability will continue on Friday, though with the
flow aloft turning westerly, that should allow for slightly cooler
and more stable air to filter into the region and push the
thunderstorm chances east of the Cascade crest. Temperatures will
be, again, a few degrees cooler, into the 70s across most of the
area with a few low 80s across the Southwest Interior.

Saturday looks to be a more typical summer day with the marine
layer in place during the morning giving way to sun in the late
morning for the rest of the day. Temperatures will be about the
same as Friday.

.LONG TERM /SUNDAY THROUGH WEDNESDAY/...An incoming shortwave
trough will move through the area Sunday into Monday bringing some
increased cloudiness as well as chances for some showers across
the area going into early next week. Overall, temperatures will be
a few degrees below normal. Chances for precipitation will be
best over the higher terrain and along the coast, but the
ensembles show some solutions that are wet while most are dry,
which aligns with the slight chance PoPs that are currently in the
forecast.

62

&&

.AVIATION...VFR for all terminals this afternoon under mostly clear
skies with some upper level cirrus overhead. Variable to
southwesterly surface flow is in place over western Washington.
There is some convection bubbling up along the southern Washington
Cascades, with multiple lightning strikes observed. There are
additional cumulus fields over the rest of the Cascades, which have
the potential to grow into thunderstorms as the afternoon
progresses. Smoke has lingered over the lee slopes of the Olympic
Peninsula, drifting aloft over the Port Angeles area. Tonight,
expect a stronger marine push to bring in stratus to western Puget
Sound. Probabilities exist but are limited in lower cigs for the
rest of Puget Sound, but have opted to include it in the TAFs for
most terminals.

On Thursday, expect the morning to have MVFR cigs throughout much of
western Washington. More thunderstorm coverage across the Cascades
and adjacent foothills is expected, but beyond the present TAF
period. This will continue to be monitored and adjusted as
necessary.

KSEA...A transition to northerly flow seems to be underway at speeds
of 6 to 8 kts. There are some mid and upper level clouds on their
way from the Oregon/Washington border that will arrive over the next
several hours. There is some convection lingering over the southern
Cascades this afternoon, but the threat for thunderstorms over the
terminal is very limited for today. Tomorrow, MVFR cigs are probable
in the morning between 13Z and 17Z. Thereafter, some clearing is
expected while watching for the threat of any thunder drifting off
the Cascades. Confidence is not high enough to include in any TAFs
at this time.

21

&&

.MARINE...High pressure will remain situated over the northeastern
Pacific and will interact with lower pressure inland over the
next several days. This will continue to promote onshore flow,
with westerly pushes expected along the Strait of Juan de Fuca
each evening. A small craft advisory remains in effect for
westerlies this evening, with sustained winds expected to be
around 25 kt, with gusts to 30 kt possible. Additional headlines
will be likely along the Strait over the next few days as the
pushes progressively get stronger.

Seas across the coastal waters will generally persist at 2-4 ft
through the weekend, with short period seas rendering steep waves
at times through tonight. A slight uptick in seas towards 3-5 ft
is possible early next week.

14

&&

.FIRE WEATHER...Warm, dry, and unstable conditions will continue
through this afternoon with minimum RH values below 30%. A few
thunderstorms have already begun to develop across the southern
Washington Cascades, but a few additional isolated thunderstorms
cannot be ruled out. The main concern from these storms will be
lightning.

The thunderstorm threat expand for Thursday with slightly higher
chances across much of the Cascades. Thunderstorm coverage should
remain just isolated enough to prohibit issuing a Red Flag
Warning, but there is still an elevated concern with thunderstorms
on Thursday. Despite the heavy downpours that are expected with
these thunderstorms, fuels are dry enough that starts from
lightning are of concern. Widespread wetting rains are not
expected. Flash flooding over burn scars, however, remain a
concern with these thunderstorms.

62

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...None.
PZ...Small Craft Advisory until 6 AM PDT Thursday for Central U.S.
     Waters Strait Of Juan De Fuca-East Entrance U.S. Waters
     Strait Of Juan De Fuca.

&&

$$