541
FXUS66 KSEW 110307
AFDSEW
Area Forecast Discussion
National Weather Service Seattle WA
807 PM PDT Wed Jun 10 2026
.SYNOPSIS...
Onshore flow will continue to keep western Washington cool
through the end of the work week, with clouds gradually
clearing by the weekend. A warm pattern via an upper level ridge
and thermal trough will build over the region this weekend into
early next week. Heat is the main concern, as highs in the 80s
and 90s result in widespread moderate HeatRisk for the region.
Additionally, dry, offshore and unstable air will produce
elevated fire weather conditions during this period. The ridge
will move inland Tuesday as onshore flow returns, slowly cooling
temperatures down.
&&
.SHORT TERM /TONIGHT THROUGH FRIDAY NIGHT/...
The latest forecast remains on track with no updates this
evening. Upper level analysis shows an upper level low and
trough axis in southeast Washington/eastern Oregon this
afternoon with a mini surface trough also in this area. Descent
onshore flow continues in wake of this low this afternoon. Quite
a bit of low level moisture has kept cloud coverage in place
(as seen on satellite). There are a couple pockets of showers in
the foothills of the Cascades this afternoon, but the steady
rain has wrapped up. Temperatures remain cool this afternoon,
with highs only reaching the low to mid 60s with the cloud
coverage in place (which will begin to erode going into the
evening as the trough axis is replaced with a shallow ridge that
will pass overhead Thursday. Winds will also switch from the
south to the north in most spots, remaining light at around 5 to
10 mph. Lows tonight cool into the 40s. More sunshine is on tap
for Thursday, with the flow remaining mostly zonal with a weak
trough passing to the north of the region. This will keep the
temperatures in the upper 60s to low 70s Thursday and Friday,
with plenty of sunshine. Lows also remain in the 40s with low to
the north shifting to the east on Friday. A ridge is expected
to build late Friday to the west, and this along with a thermal
trough underneath the ridge will be the main culprit for some
warm and dry air in the long term forecast.
&&
.LONG TERM /SATURDAY THROUGH WEDNESDAY/...
An upper level ridge remains on track to build over the region
this weekend into next week, with a thermal trough underneath it
along the coast. Ensembles have the ridge building up to
Yukon/eastern Alaska. This will result in an offshore pattern,
with temperatures warming through the weekend, peaking Monday,
before cooling down midweek next week. The hottest days will be
on Sunday and Monday, with the warmest temperatures from the
Seattle metro into the south interior, where widespread low to
mid 90s are likely. Remaining areas away from this warm region
will see highs in the mid 80s. Moderate HeatRisk remains
widespread for all but the mountain peaks on Sunday and Monday,
with portions of the south sound/interior having a 30-50% chance
of seeing major HeatRisk. This latest forecast has temperatures
slightly warmer overall, and may cause issues for those
sensitive to heat (especially given the overnight temperatures
Monday and Tuesday morning will only cool into the low 60s for
urban areas in the region.
In addition to the heat, the dry and unstable air caused by the
thermal trough will create elevated fire weather concerns
during this period (see the fire weather discussion below).
Otherwise, ensembles finally bring an onshore return on Tuesday
into Wednesday as the ridge departs to the east. The initial
onset of onshore flow will only cool off the immediate coast,
with the interior still seeing highs into the 80s on Tuesday
with moderate HeatRisk in the Seattle metro. Wednesday will see
a more widespread cooldown, with highs only reaching the low to
mid 70s in the interior. There is a 20-30% chance of a few
showers in the interior Wednesday, but overall moisture is
nonexistent in the long term.
HPR
&&
.AVIATION...
VFR across western Washington this evening with mid level clouds
and light N to W winds. Despite the light winds, the flow
aloft/onshore gradients should keep clouds forming aloft tonight
(rather than fog/mist). IFR probabilities remain greatest in the
south Cascades, Olympics and the coast with a 30-50% chance of
development. The interior terminals have a low chance (20-30%)
of MVFR ceilings in the morning, but this remains conditional
with overnight winds/cloud coverage. The period to watch for low
clouds is from 12-18Z Thursday morning. Winds increase again
Thursday 5-10 kt.
KSEA...VFR conditions through the evening. There is a 30% chance
of MVFR ceilings developing in the morning, but this is
conditional based off of overnight winds/cloud coverage into
tonight. Otherwise, VFR is likely to continue into Thursday.
Winds northwest to northeast at 4-8 kt will decrease to less
than 5 kt overnight (may become light and variable), then
increase 5-10 kt Thursday.
HPR/15
&&
.MARINE...
High pressure will rebuild offshore, with lower pressure inland
today through the end of the week. Various degrees of onshore
pushes will continue through the Strait of Juan de Fuca. The
current advisory out for the east Strait of Juan de Fuca will be
allowed to expire at 3 PM PDT this afternoon. While a couple
higher resolution ensembles hint at a couple wind gusts greater
than 20 kt this evening, confidence was not high enough to
extend the advisory (based on how winds this morning decreased
below advisory threshold with similar probabilities). Another
push Thursday evening has a higher likelihood of gusts greater
than 20 kt in the same areas.
Later this weekend into early next week, a ridge will build over
the waters, which will turn the flow north/easterly at times.
The far outer coastal waters may see winds approach 20 kt
Friday afternoon, as well as in Puget Sound/inner coastal waters
briefly on Saturday. The return of onshore flow Tuesday with the
high moving inland may result in areas of stronger winds,
particularly in the Strait of Juan de Fuca where there is an
elevated risk of gales next Tuesday (as well as small craft
winds for the coastal waters).
Seas hold around 4-6 ft for a majority of the next 7 days. A
brief uptick to 8 ft Friday may occur, as well as an increase to
8-10 ft next week Wednesday.
HPR
&&
.FIRE WEATHER...
A warm, dry and unstable pattern will setup across western WA
Saturday through Monday, with offshore flow at times. While
wetting rains will briefly help the fuels from reaching critical
thresholds this weekend for red flag conditions, minimum
relative humidity (RH) values may drop to as low as 15 to 20
percent for portions of the south sound/interior Saturday,
Sunday and Monday. These dry humidity values, combined with an
unstable airmass (via the thermal trough), and offshore winds
(although light, aiding in drying the air), will likely lead to
elevated fire weather concerns across the region this
weekend/early next week. Fuels that will be most susceptible to
the elevated fire weather concerns are dry/shrubby grassy areas
(especially those near roads), as well as piles of dry fuels.
The onshore flow will return on Tuesday, with a gradual cool
down and improvement of RH values.
HPR
&&
.SEW WATCHES/WARNINGS/ADVISORIES...
WA...None.
PZ...None.
&&
$$
NWS SEW Office Area Forecast Discussion