169
FXUS66 KSEW 102140
AFDSEW

Area Forecast Discussion
National Weather Service Seattle WA
240 PM PDT Mon Aug 10 2026

.SYNOPSIS...
Zonal flow aloft and onshore flow will maintain seasonable
conditions with morning clouds and afternoon sunshine through
Tuesday. An upper level trough will dig into the region
Wednesday, bringing cooler temperatures alongside showers and
thunderstorms over the North Cascades Wednesday and Thursday.
Warmer conditions will return by the weekend as upper ridging
rebuilds over the region.

&&

.SHORT TERM /TONIGHT THROUGH WEDNESDAY NIGHT/...
The overall weather pattern will continue to remain consistent
into Tuesday as zonal flow aloft continues. Stratus has burned
off this afternoon for most inland areas, revealing plentiful
sunshine with near-normal temperatures. Highs today across the
lowlands will peak in the mid to upper 70s, with highs in the
upper 60s along the coast. Another round of marine stratus will
expand inland overnight tonight, bringing cloudy conditions once
again Tuesday morning. The stratus layer will burn off by the
afternoon, revealing very similar conditions to today.

An upper level trough will move southward over British Columbia
and cross western Washington on Wednesday, bringing showers and
a chance of thunderstorms to the Olympics and North Cascades.
This cooler air mass will also lower temperatures several
degrees across the region, falling a couple degrees short of
seasonal normals.

&&

.LONG TERM /THURSDAY THROUGH MONDAY/...
The aforementioned upper trough will remain overhead on
Thursday with a weak shortwave rippling through. This will
likely maintain showers and isolated thunderstorm activity over
higher terrain, extending further southward across the western
Washington Cascades.

A warming trend is set to begin by the end of the work week as
weak ridging builds over the area, with high temperatures
warming into the low to mid 80s across the lowlands by Friday.
Saturday will bring more of the same, resulting in areas of
Moderate (orange) HeatRisk across the Puget Sound metro areas.
However, this will be short lived as ensembles show a slight
cool- down back to normal heading into next week.

15

&&

.AVIATION...
Westerly flow continues aloft with onshore flow in the low levels.
Stratus along the coast is expected to spread inland again tonight,
but areal coverage may be somewhat less with an earlier burn off on
Tuesday. Areas of IFR ceilings are expected across the interior
again from 12Z to 19Z before retreating to near the coast Tuesday
afternoon. Coastal areas will likely see little or no clearing on
Tuesday.

KSEA...VFR is expected through this evening. Continued onshore flow
favors a return of low clouds on Tuesday morning with IFR ceilings
12Z-18Z. Surface winds W/SW 7 knots or less will gradually veer
to the N/NW late this afternoon and evening. Winds will back to S/SW
again overnight.

27

&&

.MARINE...
Broad surface high pressure will remain centered over the offshore
waters with lower pressure east of the Cascades through much of the
week ahead. This will maintain onshore flow over the next several
days and bring diurnally driven small craft advisory strength
westerlies to the central and east Strait of Juan de Fuca daily. A
series of weak systems passing to the north of the area throughout
the week may help strengthen onshore flow at times for additional
risks of gales along the central and eastern Strait.

Seas across the coastal waters at 3-5 feet today are expected to
increase to 5-7 feet near midweek then persist within the 3-6 foot
range through the second half of the week.

27

&&

.FIRE WEATHER...
A dry, onshore flow pattern with seasonable temperatures and
persistent good to excellent overnight RH recoveries will
continue through Tuesday. Ensembles continue to very
confidently show an upper level shortwave clipping the area
Wednesday, with some variability in the strength of the
shortwave, as recent models have brought the shortwave a bit
more south over our area. This will continue the scenario of
thunderstorm potential Wednesday afternoon and evening for the
northern Cascades, as well as the central Cascade. Latest
guidance shows generally a 20-30% probability over the Whatcom,
Skagit and Snohomish Cascades through late Wednesday evening.
Warmer and continued dry conditions remain on track through the
second half of the week, likely resulting in a return of
elevated fire weather concerns for some areas. A southwest
pattern flow over the weekend may keep thunderstorm chances in
the forecast, primarily in the North Cascades.

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...None.
PZ...Small Craft Advisory until 5 AM PDT Tuesday for Central U.S.
     Waters Strait Of Juan De Fuca-East Entrance U.S. Waters
     Strait Of Juan De Fuca.

&&

$$