Colby, Washington Weather Forecast Discussion

350
FXUS66 KSEW 232142
AFDSEW
Area Forecast Discussion
National Weather Service Seattle WA
242 PM PDT Tue Sep 23 2025
.SYNOPSIS...High pressure will persist over western Washington
through mid-week, with periods of degraded air quality from
wildfire smoke. Flow towards the end of the week will become
zonal, promoting onshore flow with seasonal temperatures and
dry conditions. Chances for widespread rainfall increase into the
weekend, with a pattern change to wetter and cooler conditions by
next week.
&&
.SHORT TERM /TONIGHT THROUGH FRIDAY/...As high pressure persists
over the Pacific Northwest and a thermal trough develops northward
along the coast, flow at the surface has turned offshore. Easterly
to southeasterly winds through the Cascades has brought areas of
dense wildfire smoke to the western Cascades and lowlands east of
the Puget Sound this afternoon, causing areas of degraded air
quality. Areas of smoke will continue to linger through early
Wednesday under weak flow. Temperatures today are on track to peak
in the mid to upper 70s across the lowlands, and in the upper 60s
along the water.
Flow will begin to flatten on Wednesday as a disturbance traverses
inland over British Columbia. This will promote onshore flow by
the afternoon, bringing in slightly cooler air and additional
clouds to western Washington. The westerly flow will also help to
scour out the wildfire smoke to the east of the Cascade Crest.
Zonal flow on Thursday and Friday will bring increased onshore
flow, with a return of cloudy skies and high temperatures mostly
in the 60s. While forecast models start to show differing
solutions on Friday, ensembles maintain a slight chance of light
showers over the northern portions of western Washington.
.LONG TERM /SATURDAY THROUGH TUESDAY/...Chances for more
widespread rainfall increase throughout the weekend as an upper
level low deepens over the Gulf of Alaska and slowly traverses
southward. While chances for rain increase on Saturday, ensembles
are in better agreement over bringing in the bulk of the incoming
moisture on Sunday, with unsettled and wet conditions continuing
into next week. This will likely bring a few rounds of beneficial
rainfall to western Washington alongside near normal temperatures.
15
&&
.AVIATION...Westerly flow aloft as an upper level ridge
continues remain over the area, along with weak offshore flow. VFR
conditions continue over the area, along with areas of haze due
to offshore flow filtering in smoke throughout the interior. Most
of the haze/smoke is aloft, but will see this pattern throughout
most of the evening as flow remains light. VFR will continue
through Wednesday, with coastal terminals such as KHQM likely
seeing a brush of IFR/LIFR marine stratus briefly Wednesday
morning.
KSEA...VFR conditions this afternoon continuing through the TAF
period. Areas of smoke and haze likely around the terminal, but
should not cause any visibility issues. North winds 5 to 10 knots
this afternoon, decreasing to generally 4 to 8 knots overnight
into Wednesday morning.
Mazurkiewicz
&&
.MARINE...A broad surface ridge over the coastal waters will
continue to expand as a thermally induced trough over the coast
will shift inland tonight. Onshore flow will start to increase
late Wednesday through the rest of the week. Elevated
northwesterlies on Wednesday may lead to small craft advisory
strength winds at times.
Combined seas 6 to 8 feet decreasing to 5 to 7 feet on Thursday.
Seas look to gradually build back upwards, potentially over 10
feet into the weekend.
Mazurkiewicz
&&
.SEW WATCHES/WARNINGS/ADVISORIES...
WA...None.
PZ...None.
&&
$$

NWS SEW Office Area Forecast Discussion