Poineer Square, Washington Weather Forecast Discussion

637
FXUS66 KSEW 220342
AFDSEW
Area Forecast Discussion
National Weather Service Seattle WA
842 PM PDT Sun Sep 21 2025
.SYNOPSIS...A few lingering showers this evening will taper
overnight. Conditions will trend drier and warmer for the first
half of the week. Warmest days look to be Tuesday and Wednesday,
with typical late September weather with near normal temperatures
and potential for precipitation Friday into the weekend.
&&
.SHORT TERM /TONIGHT THROUGH WEDNESDAY/...Radar shows a few
lingering light showers this evening, mainly across portions of
the Cascades and Cascade foothills. Expect these showers to taper
over the next few hours heading into the overnight period.
Satellite imagery does indicate clearing across the southern
Sound and Chehalis River Valley tonight. With light winds and
conditions remaining moist in the low levels from this morning`s
rain, can expect areas of fog to develop overnight. Outside of
fog, areas of marine stratus are also likely develop along the
coast tonight and may push into some areas along the Chehalis Gap
and the south Sound into early Monday morning. Overall, the
forecast remains largely on track this evening, with no major
updates needed to the short and long term. The remainder of the
previous discussion follows below, with updates made to the
aviation and marine sections. 14
Further drying Monday as upper level ridging builds into the
region- helping temperatures will begin to warm as well, with
highs Monday near 70, and into the 70s to low 80s south of Olympia
and the Cascade valleys Tuesday. Lows remain in the mid 40s to
mid 50s.
.LONG TERM /THURSDAY THROUGH SUNDAY/...Upper level ridging will
keep Wednesday dry and similarly warm with highs again well into the
70s to low 80s for some locations. The grand ensembles continues to
highlight a consistent shift in the large scale pattern over the
Pacific setting the stage for more zonal flow into the Pacific
Northwest through British Columbia. Confidence continues to be good
in typical late September weather with near normal temperatures and
periods of rain and/or showers Friday into the weekend.
&&
.AVIATION...Northwest flow aloft as a trough continues eastward,
with flow weakening overnight with a brief ridge passing overhead
tonight/Monday. Conditions remain VFR across all terminals with
satellite showing continuing erosion of cloud coverage this evening.
Light northwest to northeast winds are expected to become calm or
light/variable tonight. Given the recent rains and moisture (plus
the weak gradients), this has increased confidence in IFR/LIFR
conditions tonight/Monday morning. Will be adding in lower VIS
and/or CIGs to the TAFs for a majority of terminals tonight (highest
confidence remains the south interior up through the Olympics into
the north Puget Sound terminals, with moderate confidence of lower
obstructions into the major Puget Sound terminals). Expected
development time is roughly 12-15Z with clearing back to VFR 17-
20Z. Light northwest winds 4-6 kt will pick up late Monday
morning/afternoon.
KSEA...Still VFR this evening with a mix of broken to scattered
clouds at around 5,000 ft slowly eroding on satellite. Winds are
still out of the northeast but will become very light out of the
south tonight Models have this cloud coverage hanging, and lowering
down to MVFR after 13Z, with a period of IFR/LIFR conditions
possible from 14Z-17Z (given the environment, will include a period
of lower VIS and CIGs during this window). Clearing to VFR will take
place 18-20Z with most CIGs eroding. Winds will become light
northwesterly 4-6 kt.
HPR
&&
.MARINE...High pressure is expected to build back over the waters
tonight into Monday with lower pressure inland returning onshore
flow. The small craft advisory for the central/east Strait of Juan
de Fuca will expire at 10 PM (06Z) tonight as west winds continue to
decrease. Seas remain at 7-8 ft with periods at 11 seconds in the
coastal waters (while a few shorter periods and higher wave heights
will be possible, guidance shows seas decreasing down to 5-7 ft
Monday evening with periods staying at 11 seconds). The remainder
of the outlook remains benign with a weak front dissipating to
the north of the waters midweek, and seas remaining in the 5-7 ft
range. Some shorter periods of 8-10 seconds are possible midweek
behind the front.
HPR
&&
$$
.SEW WATCHES/WARNINGS/ADVISORIES...
WA...None.
PZ...Small Craft Advisory until 11 PM PDT this evening for Central
     U.S. Waters Strait Of Juan De Fuca-East Entrance U.S.
     Waters Strait Of Juan De Fuca.
&&
$$

NWS SEW Office Area Forecast Discussion