981
FXUS66 KSEW 130311 CCA
AFDSEW

Area Forecast Discussion
National Weather Service Seattle WA
810 PM PDT Sat Jul 12 2025

.SYNOPSIS...Warm and dry conditions will continue through the
weekend with upper level ridging over the region. A brief reprieve
in temperatures is likely on Monday as a system slides southward
from British Columbia and skirts the area. Warmer and drier
conditions are expected again around midweek, with highs potentially
reaching the 90s for some lowland locations.

&&

.SHORT TERM /TONIGHT THROUGH TUESDAY/...Shallow stratus hugs the
immediate coastline this evening. The HQM/SEA gradient is less than
a millibar this evening which spells only a minor intrusion of the
marine layer overnight...perhaps to Shelton. Thermally induced low
pressure will remain over the interior into Sunday...with Seattle
metro southward as well as the warmer Cascade valleys in the 85 to
90 degree range after mild overnight lows in the upper 50s to lower
60s. This will put a good swath of the interior lowlands into
moderate HeatRisk before an upper trough swinging by to the north
brings us a very short term cooling trend for Monday. The heat
returns shortly thereafter with the latest ensembles giving Seattle
southward a decent shot at back-to-back 90+ degree days midweek next
week. Current forecasts are on track. Previous discussion follows
with updates to marine/aviation portions.

Upper level ridging over the region will continue promote warm and
dry conditions across western Washington today and Sunday. Modest
onshore flow will continue into Sunday for some morning stratus, but
do not expect as much cloud cover across the area as this morning.
Afternoon high temperatures today will climb into the upper 70s to
mid 80s across the interior and into the upper 60s to low 70s along
the coast. Highs look to climb a few degrees on Sunday as ridging
starts to amplify offshore, with temperatures looking to top out in
the 80s to low 90s across the interior and in the 70s along the
coast. Morning lows on Sunday will generally be in the 50s for most
spots, but may not dip down past the low 60s for the urban corridors
east of the Sound (generally from Tacoma to Everett). As a result,
Moderate HeatRisk will be present across the majority of the
interior lowlands.

A brief reprieve in temperatures is likely on Monday as a positively
tilted trough slides down across British Columbia and skirts western
Washington. Outside of a slight chance of showers across the far
Northern Cascades, this system will not bring much in the way of
precipitation, but will mostly bring additional cloud cover and an
increase in onshore flow in the low levels. High temperatures are
expected to be roughly 5 to 10 degrees cooler areawide- with
afternoon highs expected to be in the mid 70s to low 80s across the
interior and in the 60s along the coast.

The next warm up commences on Tuesday as high pressure offshore
starts to build back into the area. Afternoon highs will rebound
into the 80s for the majority of the interior lowlands, with
temperatures along the coast expected to climb into the upper 60s to
mid 70s. This will again bring another round of Moderate HeatRisk to
portions of the interior lowlands.

.LONG TERM /WEDNESDAY THROUGH SATURDAY/...Wednesday currently
looks to remain the warmest day of the week, with the most
widespread Moderate HeatRisk across the area. Under the influence of
high pressure and a thermal trough at the surface, expect
temperatures to climb into the upper 80s to low 90s across the
interior lowlands. Areas along the coast will warm as well, but will
mainly be in the 70s. This warm and dry trend could bring elevated
to critical fire weather conditions during this time frame- see the
fire weather section below for more details.

Ensembles continue to have a tough time converging on solutions
after Wednesday, though the ensemble mean has started to indicate
some weak troughing over the area by Thursday and Friday. The
overall trend leans towards temperatures cooling a few degrees both
Thursday and Friday. However, with highs still expected to be in the
80s across the interior lowlands into the weekend, temperatures look
to continue to trend above normal through the long term at this
time. 14

&&

.AVIATION...Northwest flow aloft through the period as upper-ridging
holds stubbornly offshore. Widespread VFR conditions this evening
with a few high clouds starting to enter the area. Mostly clear
skies are expected tonight into Sunday also but can`t rule out
patchy fog along with stratus along the immediate coast, including
HQM. Northerly winds for interior terminals around 8 to 12 kt. KCLM
and KHQM looks to remain westerly with similar magnitudes. Winds
become lighter overnight.

KSEA...VFR conditions today and throughout the TAF period. North-
northwest winds this evening generally between 8 to 12 kt have been
slow to subside but are still expected to trend lighter by 06z.
Speeds increase again Sunday afternoon with gusts up to 20 kt.

McMillian/18

&&

.MARINE...Surface high pressure continues offshore with low level
onshore flow through area waters. A westerly push this evening will
be weaker than the previous days but still seeing some speeds in the
Strait and nearshore coastal waters still showing borderline SCA
speeds. As such, inherited headlines will remain in place. Diurnally
driven pushes will continue through the Strait into early next week.
The next best chance for SCA level (possibly near gales) winds
through the Strait and Admiralty Inlet appears to be Sunday evening.
Northerly winds will increase over the outer coastal waters Sunday
night with the potential to reach small craft advisory strength as
well along with steep seas. Weak offshore is showing signals towards
midweek as a thermal trough builds along the coast.

Combined seas 4 to 6 feet will gradually increase to around 6 to 8
feet late Sunday into Monday. Seas look to remain elevated for the
first half of next week.

McMillian/18

&&

.FIRE WEATHER...High pressure over the region will maintain warm
and dry conditions across Western Washington this weekend. Modest
onshore flow will provide for excellent overnight recoveries for
most of the lowlands. However, Sunday afternoon will see RH values
dip down into the 25-30% range for areas in the interior. A weak
trough slides through the region on Monday, boosting cloud cover
and humidities, as well as bringing cooler temperatures into the
region. This is a short break as elevated fire weather concerns
return by the middle of next week, with minimum RH values
approaching critical thresholds. While flow remains mostly
northerly or northeasterly, the combination of daytime breezes
overlaying the lowest RHs may elevate concerns around Wednesday
and Thursday for much of Western Washington as a thermal trough
may build over the region. This could further enhance instability
as well. That said, ensemble guidance continues to exhibit a wide
range of potential outcomes for this time period and confidence
remains a bit lower in the details of potential elevated or
critical conditions during the middle to late portion of next
week. Cullen

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...None.
PZ...Small Craft Advisory from 3 PM Sunday to 6 AM PDT Monday for
     Central U.S. Waters Strait Of Juan De Fuca-East Entrance
     U.S. Waters Strait Of Juan De Fuca.

     Small Craft Advisory from 5 PM Sunday to 3 AM PDT Monday for
     Admiralty Inlet.

&&

$$