507
FXUS66 KSEW 192311
AFDSEW

Area Forecast Discussion
National Weather Service Seattle WA
411 PM PDT Tue Aug 19 2025

.SYNOPSIS...Cooler and cloudier conditions will continue today,
with some light showers possible along the coast and the North
Cascades. High pressure will build over the Pacific Northwest late
this week and remain situated across the region through the
weekend for warmer and drier conditions.

&&

.SHORT TERM /TONIGHT THROUGH FRIDAY/...A few light showers will
remain possible this evening across portions of the interior and
North Cascades as an upper level low moves into British Columbia
and a weak frontal system moves across western Washington.

Conditions will remain cool and cloudy heading into Wednesday as
the upper level low makes its way across British Columbia and weak
troughing remains over western Washington. Clouds will clear
through the morning hours for a sunnier afternoon and highs
will be in the 60s along the coast and in the low to mid 70s
across the interior.

High pressure will then build into the Pacific Northwest Thursday
and amplify across the region on Friday for a warming and drying
trend across western Washington. Afternoon highs will climb into
the 70s along the coast and into the mid 70s to low 80s across the
interior. By Friday, highs will climb into the upper 70s along
the coast and 80s to low 90s across the interior, resulting in
widespread Moderate (Orange) HeatRisk across the area.

.LONG TERM /SATURDAY THROUGH TUESDAY/...Heat will continue to be
the main weather impact heading into the weekend as high pressure
remains situated across the region. At this time, Saturday looks
to be the warmest day across the interior, with highs expected to
be in the 80s to low 90s. While morning lows will mainly be in
the 50s, some urban areas may not dip below 60. With little
relief in the heat overnight, widespread Moderate HeatRisk will
continue.

Temperatures look to remain warm across the interior heading into
Sunday, with highs expected to be in the 80s and even low 90s
along the Cascade valleys and lows expected to be in the 50s to
low 60s. The spread in temperatures becomes greater and confidence
in the weather pattern becomes lower heading into early next
week where ensembles remain split between an upper level shortwave
developing over the northeastern Pacific and the ridge holding
strong over the area. Will need to see how ensemble solutions
resolve over the next few days as this will have a direct impact
on the duration of the heat across the area.

14

&&

.AVIATION...A weakening front and upper level trough will continue
to swing through western WA this afternoon and evening. Reflectivity
on radar was showing a small corridor of high showers (likely
falling as virga) from Aberdeen through east of Bellingham and
generally funneling northeast with some midlevel moisture. Clouds are
the main thing with mid and high level cloud decks this afternoon
(only exception is the coast with some IFR at KUIL). A weak marine
push is expected to bring stratus inland tonight between 12-18Z,
with medium confidence that interior terminals will see MVFR clouds
around 2,000 ft tomorrow morning (NBM gives ~40% chance). The chance
increases further west, as does the chance of IFR/LIFR conditions
along the coast Wednesday morning into as far as the Olympics.
Complete clearing is expected after 18Z, as the trough departs and a
ridge begins to build off the coast of B.C, turning the flow aloft
northwesterly. Surface winds tonight will turn from west to
northerly through the evening 4 to 8 kt (few gusts in the Strait of
Juan de Fuca possible to 15 kt), becoming light, then picking up 5-
10 kt by Wednesday afternoon.

KSEA...VFR continues this afternoon with the weak front moving
through. Cloud ceiling will remain at a mid to high level through
the evening. Winds have become variable to the north at KBFI, so
will most likely see a shift of north winds between 00-02Z Wednesday
(on a decreasing trend to below 5 kt). NBM gives a 40% chance of
MVFR Cigs tomorrow morning (will likely be a broken layer as the
marine push is not expected to be super strong). Clearing will take
place after 18Z, and north winds will pick up 5-10 kt in the
afternoon.

HPR

&&

.MARINE...A weakening front is in progress across much of the
waters, and will move onshore this evening into Wednesday. A weak
marine push will produce a few breezy winds through the Strait of
Juan de Fuca, but it remains very likely at this time that sustained
and wind gusts will remain below 20 kt. Later in the week, a
thermally induced trough will expand northward along the coast
Thursday/Friday, then move inland on Saturday. Winds will turn
northerly over the coastal waters, and may be a touch breezy in the
outer coastal waters but not reaching the need for an advisory. Seas
will remain at 3 to 4 feet this week, increasing to 4 to 6 feet next
weekend.

HPR

&&

.FIRE WEATHER...An upper level ridge building over the area late
this week and into this weekend will bring warm and dry conditions
to western Washington. Periods of offshore flow will be possible
on Friday and Saturday, helping to dry out fuels from recent rains.
Elevated fire weather conditions are expected across portions of
the Cascades and for areas south of the Sound through the weekend
with high temperatures in the upper 80s to low 90s and minimum
RHs dipping into the 20-30 percent range during the day.

14

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...None.
PZ...None.
&&

$$