718
FXUS66 KSEW 211641
AFDSEW

Area Forecast Discussion
National Weather Service Seattle WA
941 AM PDT Fri Aug 21 2026

.SYNOPSIS...One more warm day today with Western Washington on
the back side of an upper level ridge. Upper level low
approaching from the southwest will move into the coastal waters
Saturday and into Southern British Columbia early Sunday
morning. This system will bring cooler weather with a chance of
showers and thunderstorms Saturday. Upper level ridge rebuilding
Sunday will move east Monday and Tuesday. An upper level trough
will arrive Wednesday.

&&

.SHORT TERM /TODAY THROUGH SUNDAY/...The current forecast
remains on track with no planned updates this morning. 33

Previous discussion...Satellite imagery shows stratus confined
to the coast and Lower Chehalis Valley early this morning. Clear
skies over the remainder of the area. Temperatures at 3 am/10Z
were in the mid 50s to mid 60s.

Upper level low centered off the Northern California coast
early this morning will continue to move slowly northeast today.
Resulting upper level ridge out ahead of the low giving Western
Washington southerly flow aloft. High clouds embedded in the
flow aloft moving over the area later today. Light surface
gradients this morning with the stratus deck not getting much
further east. By midday the stratus deck will be just off the
coast. High clouds this afternoon could knock a couple of
degrees off the highs versus yesterday with highs in the mid 70s
to mid 80s inland and mid 60s to lower 70s along the coast.

Upper level low off the Northern Oregon coast by 12z Saturday.
Upper level disturbance spinning out of the low moving into the
southwest portion of the area in the early morning hours for a
chance of showers. Lows in the 50s and lower 60s.

Upper level disturbance making it`s way through the remainder of
Western Washington Saturday morning into the early afternoon
hours. Chance of showers and thunderstorms with this feature.
Fire weather watch for the Olympics and North Cascades will
continue with this forecast package. By late afternoon the
feature will be far enough to the north for the chances of
convection to be north of Seattle. Cloudy skies will keep
temperatures well below normal. Highs in the 60s and lower 70s.

Low moves inland into Southern British Columbia early Sunday
morning. Chance of showers and thunderstorms continuing north
of Seattle with the thunderstorms threat coming to an end in
the overnight hours. Low level onshore flow will keep skies
mostly cloudy behind the feature. Lows in the 50s.

Chance of showers lingers near the Canadian border Sunday
morning as the low weakens and moves northeast. Low level
onshore flow continuing keeping cloud cover over the area at
least through the morning hours. Highs a little warmer than
Saturday but still below normal, mid 60s to mid 70s. Felton

&&

.LONG TERM /SUNDAY NIGHT THROUGH THURSDAY/...Upper level ridge
building over the area Sunday night moving east Monday. Western
Washington remaining on the backside of the ridge Tuesday.
Models playing push it back with next upper level trough now
timed into the area Wednesday instead of Tuesday on previous
runs. Lots of variability with this feature. A few of the
ensembles having wetting rain over the northern portions
Wednesday. A vast majority of the ensemble solutions going for a
chance of showers scenario. In the lower levels varying degrees
of onshore flow. At this point Tuesday looks to be the warmest
days with highs in the 70s and lower 80s for the interior. Highs
mostly in the 70s on the other days. Highs on the coast in the
mid to upper 60s.

There has been no measurable rain at Seattle-Tacoma airport this
month. just a trace on the 1st. Having a dry first three weeks
of August in Seattle is not that common. This year will be the
9th time in the 82 year history of weather records at Seattle-
Tacoma airport. The last time it happened was 2012. This year
will only be the 3rd time in the last 40 years. Felton

&&

.AVIATION...Southerly flow aloft will increase tonight as an upper
low approaches Western Washington. VFR conditions this morning for
the majority of the area, with LIFR/IFR stratus along the coast.
High clouds will increase today as the upper low moves towards the
region. MVFR/IFR stratus will move inland tonight into Saturday
morning, spreading into portions of Puget Sound. LIFR stratus will
also exist at times along the coast. A few showers may also develop
late tonight, and more so on Saturday, with the a lower probability
for thunderstorms (10 to 20 percent) for all terminals. Light W/NW
winds increase from the W/SW tonight and Saturday.

KSEA...VFR with increasing high clouds through this evening. Stratus
will spread inland early Saturday morning, reaching the terminal
around 11-12z. Low-end MVFR to IFR cigs expected Saturday AM with
improvements to VFR into the afternoon. N/NW surface winds between 4
to 6 kts into this afternoon, transitioning SW approximately 00z
through Saturday. JD

&&

.MARINE...Broad high pressure over the waters will weaken
Friday. A weak surface low will move into the coastal waters
Saturday with the associated system moving through the inland
waters Saturday morning into early afternoon. The low will
dissipate Saturday night. Additionally, there is a slight chance
(10-20%) for thunderstorms on Saturday for both the coastal
waters and interior waters. High pressure will rebuild Sunday
and remain over the area through Monday. A cold front will move
over the waters on Tuesday.

Winds will pick up behind the system on Saturday. Guidance suggests
there is a 40-60% wind gusts may approach near 21 kt through the
Strait of Juan de Fuca, with winds above 21 kt staying on the
Canadian side.

Seas remaining mostly in the 3 to 5 foot range for the next few
days. Felton/29

&&

.FIRE WEATHER...
Dry and warm conditions continuing today. Tomorrow`s thunderstorms
have been the main headline but, some instability is modeled to be
present in the atmosphere today. RAP analysis shows 0-3 km lapse
rates around 7-9 C/km this afternoon along the Cascades. Min RHs
this afternoon may also get near critical thresholds but increasing
high will help to mitigate the threat. Upper level low offshore
moving northeast ending up off the Washington coast early Saturday
morning. Convection developing with this feature early Saturday
morning over the southwest portion of the area.
Convection spreading over the entire area by mid to late Saturday
morning. Probabilities for convection are highest over the Olympics
and North Cascades, peaking between 20 to 30 percent. Due to the
potential of scattered thunderstorms for these areas and the very
dry conditions at the surface, a Fire Weather Watch will continue
for zones 652, 658, and 661. Convection may exist elsewhere however
uncertainty exists in the coverage. Lightning may lead to new fire
starts, as well as result in gusty and erratic winds.

Low level onshore flow increases Saturday night into Sunday with
varying degrees of onshore flow through the middle of next week.
Good relative humidity recoveries each night will keep fire weather
concerns at a minimum. Chance of showers in the middle of the week
with an upper level trough moving into the area.

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...Fire Weather Watch from late tonight through Saturday evening
     for West Slopes of the North Cascades Generally above
     1500 Feet.

     Fire Weather Watch from late tonight through Saturday evening
     for East Portion of the Olympic Mountains-West Portion of
     the Olympic Mountains.

PZ...Small Craft Advisory from 6 PM this evening to 6 AM PDT
     Saturday for Central U.S. Waters Strait Of Juan De Fuca-
     East Entrance U.S. Waters Strait Of Juan De Fuca.

&&

$$