701
FXUS66 KSEW 010302
AFDSEW

Area Forecast Discussion
National Weather Service Seattle WA
802 PM PDT Sun Aug 31 2025

.UPDATE...A few thunderstorms are popping up over the San Juans
and northern Whatcom county that are quickly moving up into
Canada. A few thunderstorms will be possible in this area for the
the next few hours before the energy continues to move north and
daytime heating wears off. No updates to the general forecast this
evening, see below for updates to aviation.

&&

.SYNOPSIS...An upper level low continues to churn offshore which
will continue to provide a slight chance for showers and possibly
isolated thunderstorms over the North Cascades this evening. Upper
level ridging will nudge back into our area starting on Monday
with dry and warm conditions. Temperatures will continue to warm
through midweek, where well above temperatures are expected across
much of the area.

&&

.SHORT TERM /TONIGHT THROUGH WEDNESDAY/...An upper level low
continues spin offshore, which has kept mid to high level clouds
streaming in this afternoon and temperatures fairly seasonable
across much of the area. High temperatures this afternoon will
generally be in the mid to upper 70s. Along with reasonable
temperatures, some elevated instability can be noted across some
of the area, with some isolated thunderstorms popping up earlier
this morning. Hi- resolution models have since struggled this
afternoon, but with recurring instability, there still remains a
10-15% chance of an isolated thunderstorm or two, primarily in the
North Cascades throughout this evening. The isolated thunderstorm
threat will decrease throughout the overnight hours and vanish by
Labor Day.

The aforementioned low pressure system offshore will still
continue to influence temperatures on Monday, with a round of
morning clouds expected, high temperatures will still continue to
be in the mid to upper 70s with areas of sun later on in the day.

Upper level ridging will start to nudge its way into western
Washington on Tuesday, with warmer and drier conditions expected
throughout much of area. Temperatures will warm on Tuesday
afternoon generally to the lower to mid 80s throughout the
interior, with low to mid 70s for areas along water. Areas in the
Cascade Foothills will see warmer temperatures as weak offshore
flow warms temperature in the upper 80s to lower 90s. Areas of
Moderate (Orange) HeatRisk can be expected on Tuesday through some
areas of the interior, with Minor (Yellow) HeatRisk elsewhere.

As we get into Wednesday, temperatures will warm even further,
with temperatures hovering in the mid to upper 80s throughout the
interior. The warmest temperatures will be located in the Cascade
Foothills in the low to mid 90s, where localized areas of Major
(Red) HeatRisk can be found. Elsewhere, Moderate (Orange)
HeatRisk can be expected through all of the interior. Yellow
(Minor) HeatRisk will be found along the coast and areas along the
water.

.LONG TERM /THURSDAY THROUGH SUNDAY/...Upper level ridging will
still remain the weather feature throughout the long term, but
ensemble guidance is having trouble on the breakdown of the ridge
or if troughing offshore starts to move closer to W WA. Ensembles
have been picking up on a shortwave moving through the area on
Thursday which would cool down temperatures a few degrees.
Temperatures look to steadily cool down into the weekend with
potential troughiness starting to influence our weather pattern.
For now, have stuck to the NBM which corresponds to slightly
cooler temperatures with dry conditions.

Mazurkiewicz

&&

.AVIATION...An upper level low will continue to rotate just offshore
into Monday producing southerly flow aloft over Western Washington.
Low level onshore flow continues near the surface and this will pull
a marine layer inland overnight for widespread low MVFR or IFR
ceilings across the interior lowlands on Monday morning. The stratus
will burn off across most of the interior 18Z-20Z Monday, but will
likely linger along the coast for most of the day.

KSEA...VFR as of 03Z, but stratus is making fairly rapid progress
inland and will likely need to speed up arrival time of IFR/low MVFR
ceilings at the terminal...probably around 08Z. Low clouds will hang
around until midday Monday then scatter out to VFR by around 20Z.
Surface winds light S/SW veering W/NW 5 to 7 knots by mid to late
Monday afternoon. 27

&&

.MARINE...An onshore flow pattern will continue through this week.
Onshore flow will vary in intensity, resulting in westerly pushes
through the Strait of Juan de Fuca most evenings. A Small Craft
Advisory remains in effect for the central and eastern portions of
the Strait of Juan de Fuca this evening into tonight with gusts to
25 kts. Westerly winds will remain elevated then the next few
evenings, and will need to monitor for any additional SCAs due to
wind gusts. Northerly winds will also increase for the Coastal
Waters late Tuesday through late week.

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

&&

.FIRE WEATHER...A slight chance of dry thunderstorms is
still in the forecast for the Cascades this evening, with an outside
chance of lingering into Monday. A low pressure system parked
offshore will send a weak impulse into the area, steepening the
lapse rates and offering some ascent, although weak. There is no
significant source of moisture, increasing concern over dry
lightning strikes. 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%. The thunderstorm threat drops
off considerably into Labor Day and early this week.

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. A
weak shortwave trough may increase thunderstorm threats on Thursday,
but that forecast can and will change between now and then. Elevated
concerns for hot, dry and unstable conditions will persist through
much of the mid to late week period.

21

&&

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

&&

$$