Spanaway, Washington Weather Forecast Discussion

159
FXUS66 KSEW 180955
AFDSEW
Area Forecast Discussion
National Weather Service Seattle WA
255 AM PDT Thu Sep 18 2025
.SYNOPSIS...Onshore flow will maintain near normal temperatures
across western Washington with morning clouds and afternoon sun
breaks. The next system will arrive on Saturday, bringing
widespread rain and breezy winds to the region. Conditions will
dry out early next week as high pressure builds into the region.
&&
.SHORT TERM /TODAY THROUGH SATURDAY/...Cooling will continue today
as onshore flow strengthens, with temperatures peaking in the 60s
to low 70s across the region. While conditions will stay dry,
marine stratus will continue to expand inland this morning and
erode by the afternoon to reveal mostly clear skies. However,
wildfire smoke will continue to impact the region, most notably
near the Bear Gulch fire in the Olympics. As weak troughing moves
over the area today, winds overhead will shift northerly, which
will direct the smoke southward towards Shelton and southward
along the I-5 corridor. Areas in the Cascades can also expect to
see hazy skies due to wildfire smoke throughout the day.
Weak ridging will build into the region on Friday, bringing an
additional day of more of the same. Temperatures will peak a few
degrees above normal, with another round of morning stratus,
afternoon sun, and areas of smoke.
The next weather system will move into the region on Saturday as a
cold front moves inland. Rain will reach the coast by the
afternoon, filling inland by the late evening. As the cold front
swings across western Washington, winds will become breezy with
gusts reaching 20 to 30 mph.
.LONG TERM /SUNDAY THROUGH WEDNESDAY/...An upper level trough will
continue to dig into the region on Sunday, maintaining unsettled
weather through the weekend. The bulk of the moisture will fall
overnight into Sunday morning, with lingering showers over the
mountains Sunday afternoon. Ensembles remain fairly steady over
rainfall estimates through Sunday, with a third to half an inch of
rain over the lowlands and up to 2 inches over the Olympics and
Cascades.
Ridging will build into the region to start off next week, with
some uncertainty over potential precipitation. Operational models
continue to dry things out through Wednesday, while ensembles
maintain a chance for rain along the northern Olympic Peninsula
and northern interior Monday with another incoming system on
Wednesday. Temperatures are on track to stay on the mild side
through the period.
15
&&
.AVIATION...Southwesterly flow becoming northwesterly tonight as an
upper level trough moves across the area. VFR conditions for most
terminals early this morning with some patchy low clouds starting to
develop. Onshore flow is slowly easing this morning, otherwise the
more sheltered terminals are seeing calm winds. Clouds have been
slow to develop and lower so far this morning, but expecting broken
ceilings to develop across the area by 13-15Z. The coast will be
MVFR to IFR, with mostly VFR to locally MVFR expected through the
interior terminals. Any stratus that does develop should evaporate
quickly, leaving VFR conditions with mostly clear skies for most of
the day today. Guidance is hinting at another round of low stratus
for the coast and fog-prone locations again tomorrow morning as we
begin to get more subsidence and weaker winds over the region. Winds
tomorrow will be N/NE through the interior, NW along the coast, at
around 8 to 14 kt. This will keep smoke out of CLM, but could
introduce near BLI and SHN.
KSEA...VFR conditions through most of the TAF period. Mostly clear
skies with high clouds through today and tonight. The only exception
being a brief period where some low clouds may fill in. Clouds have
been slow to develop, so have trended more optimistically in the TAF
for just of a few hours of BKN035 with some patchy mist. Any stratus
that does develop should clear out quickly after 17Z. Will continue
to monitor trends and alter if needed. Northeast winds around 5 kt
will increase late this morning to northwest 8 to 12 kt this
afternoon and evening.
62
&&
.MARINE...Onshore flow continues to ease this morning following a
frontal passage yesterday morning. High pressure will rebuild over
the coastal waters today and into Friday. Another cold front will
increase winds and bring rain to the area waters this weekend.
Southwesterly winds will increase across the entire area, but the
best chances for seeing Small Craft Advisory level winds will be
through the central portions of the Strait of Juan de Fuca, from
Saturday afternoon as the front moves though, and behind the front,
through much of Sunday. Winds may briefly hit SCA criteria for a few
hours as the front moves through the interior waters from the Puget
Sound up through the northern interior waters. Winds look to ease on
Monday through additional systems may approach the waters next week.
Seas are sitting around 8 to 10 ft across the waters this morning,
but should slowly decrease this morning as winds also ease below
Small Craft Advisory criteria. The advisory will continue through
this afternoon, primarily for the outer coastal waters. Seas
decrease to 6 to 8 ft tonight, becoming 4 to 5 ft Friday. Seas will
once again bump up to 7 to near 10 ft this weekend as the frontal
system moves through. Seas return to 6 to 8 ft next week.
62
&&
.SEW WATCHES/WARNINGS/ADVISORIES...
WA...None.
PZ...Small Craft Advisory until 5 PM PDT this afternoon for Coastal
     Waters From Cape Flattery To James Island 10 To 60 Nm-
     Coastal Waters From Cape Flattery To James Island Out 10 Nm-
     Coastal Waters From James Island To Point Grenville 10 To
     60 Nm-Coastal Waters From James Island To Point Grenville
     Out 10 Nm-Coastal Waters From Point Grenville To Cape
     Shoalwater 10 To 60 Nm-Coastal Waters From Point Grenville
     To Cape Shoalwater Out 10 Nm.
&&
$$

NWS SEW Office Area Forecast Discussion