855
FXUS66 KSEW 122259
AFDSEW

Area Forecast Discussion
National Weather Service Seattle WA
359 PM PDT Wed Aug 12 2026

.SYNOPSIS...
Showers and thunderstorms will continue over the mountains
over the next several days under the influence of an upper level
trough. Southwest flow aloft will develop over the weekend,
bringing some warming ahead of another weak trough at the
beginning of next week that will likely bring slightly cooler
and unsettled conditions.

&&

.SHORT TERM /TONIGHT THROUGH FRIDAY NIGHT/...
An upper level trough will remain overhead over the next
several days as onshore flow continues at the surface, resulting
in fairly similar conditions between today and Friday. The
marine stratus layer has eroded towards the coast for most
inland locations, with enough instability this afternoon to
generate showers and thunderstorms over the Olympics and western
Cascades. While relative humidities in the mountains remain
fairly high as a result of continued onshore flow, fuels are dry
enough to cause concern with incoming lightning. The potential
for abundant lightning and gusty and erratic outflow winds has
resulted in the issuance of a Red Flag Warning through this
evening. For more details, see the FIRE WEATHER section below.

The region will see another round of low stratus expanding
inland tonight, though the stratus layer is not expected to
linger too long into the morning Thursday for most inland areas.
Continued instability under the influence of the upper level low
will maintain chances for afternoon showers and thunderstorms
over the Olympics and Cascades, and a Fire Weather Watch has
been issued for these areas for Thursday, once again for the
potential for abundant lightning and gusty outflow winds. More
of the same can be expected on Friday, with morning stratus and
chances for showers and thunderstorms over the mountains.
Elsewhere across the lowlands, conditions will remain mild with
light winds and mostly clear skies through the remainder of the
week.

&&

.LONG TERM /SATURDAY THROUGH WEDNESDAY/...
Models remain in good agreement with southwest flow developing
aloft over the weekend as a high pressure ridge builds over the
southwestern US and a cutoff low drops southward offshore. While
temperatures will remain mild, the southwest flow may open the
door for moisture to advect into the region, with continued
potential for afternoon thunderstorms to develop. By the start
of next week, a trough axis is favored to cross western
Washington, with slightly cooler temperatures and more
widespread chances for light shower activity. However, model
solutions start to show a larger spread of solutions beyond the
weekend, so conditions into next week remain uncertain.

15

&&

.AVIATION...
Shortwave trough remains overhead the terminals today, with flow
switching from southwest to northwest as it transits to the east.
VFR conditions primarily for most stations this afternoon (except
for the coast where stratus remains present and will remain so down
to IFR). Few popcorn isolated cells will continue to form in the
north Cascades and Olympics this afternoon with no impacts expected
for nearby terminals. Winds have transitioned to the west/northwest
around 5-10 kt, and will decrease to 5 kt out of the southwest
tonight/Thursday morning. LAMP guidance maintains a 30-40% chance of
MVFR in the interior Puget Sound terminals from 12Z-18Z, with a 10-
20% chance of IFR. Probabilities for IFR/LIFR increase significantly
moving west into the Kitsap, and towards the coast. Additionally,
smoke will increase aloft from fires in B.C., but impacts down
towards the surface remain minimal.

KSEA...VFR through tonight, then a 30-40% chance of MVFR ceilings
between 12Z and 18Z Thursday morning (10-20% chance for a drop into
IFR). Northwest winds 5-10 kt will decrease to 5 kt this evening,
becoming southwest overnight, and northwest again late Thursday
morning/afternoon 5-10 kt.

HPR

&&

.MARINE...
High pressure in the Pacific will begin to weaken by the end of the
week and into the weekend as it gets pushed southward with an
approaching trough offshore that will slowly move towards land as it
splits early next week. Diurnal pushes through the Strait of Juan de
Fuca remains the primary impact, although small craft impact
potential remains low until Friday afternoon and this weekend. Winds
in the coastal waters will decrease going into the weekend as
pressure gradients decrease.

Seas at 2-4 ft with a brief uptick to 6 ft in the outer coastal
waters tonight into Thursday, and early next week.

HPR

&&

.FIRE WEATHER...
A Red Flag Warning has been issued for today for the north Cascades
and Olympic Mountains. A Fire Weather Watch has been issued for
the same area plus the southern Cascades for Thursday.

Fire weather concerns will remain elevated to critical at times as
an upper level trough will remain over the area today through
Friday, creating weak instability in the atmosphere. This is
bringing onshore flow with higher humidity but also chances of
thunderstorms. Area thunderstorm chances have increased for the
period, as high as 50-70% over the mountains. Some heavier showers
are locally possible with the thunderstorms that, if they last long
enough in one place, would put down wetting rains or more. There is
a low but non-zero threat of flash flooding and debris flows in burn
scars. Fire weather concerns moderate over the weekend.

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...Red Flag Warning until 11 PM PDT this evening for East Portion
     of the Olympic Mountains-West Portion of the Olympic
     Mountains-West Slopes of the North Cascades Generally
     above 1500 Feet.

     Fire Weather Watch from Thursday morning through Thursday
     evening for East Portion of the Olympic Mountains-West
     Portion of the Olympic Mountains-West Slopes of the
     Central Cascades Generally above 1500 Feet-West Slopes of
     the North Cascades Generally above 1500 Feet.

PZ...None.

&&

$$