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000
FXUS66 KSEW 011604
AFDSEW

Area Forecast Discussion
National Weather Service Seattle WA
904 AM PDT Sun Oct 1 2023

.UPDATE...No major changes to the forecast. Patchy to dense fog is
ongoing in isolated areas of Puget Sound in Hoquiam, Olympia,
Lake Stevens, and outside of Tacoma. The fog will continue through
the late morning/early afternoon. Remaining areas will see low
ceilings through the same timeframe. The clearing this afternoon
will be short-lived however, due to the next surface system
approaching from the west for tomorrow. The cold front for Monday
will bring in the next chance of showers for the region, before
mostly drying out the remainder of the week.

HPR

&&

.SYNOPSIS...High pressure will remain over Western Washington
today with seasonable temperatures and another dry day. A weak front
brings some rain chances to the region on Monday and possibly
lingering into Tuesday. High pressure will then rebuild over the
region by mid-week, maintaining dry conditions and a warming trend.

&&

.SHORT TERM /TODAY THROUGH TUESDAY/...This morning not too
terribly different from those of the past couple days, brisk
morning temperatures, scattered spots of patchy fog and nothing in
the way of precip on the radar. The ridge that has been the main
influence of W WA weather will shift southeastward throughout the
day today allowing the next incoming system...a weakening
front...to reach the coast late tonight. Models remain consistent
in breaking the feature up over the area as it passes through on
Monday, resulting in a mix of high-end PoPs and fairly low QPFs.
Translation, there will be widespread showers, but not much in the
way of rainfall will be associated with them. Deterministic and
ensemble models continue to think there will be at least some
lingering moisture going into Tuesday, but both PoPs and QPF look
paltry at best.

While today will see temps peaking for the current warming trend,
they likely will not be the warmest of the forecast period, as per
Long Term discussion below. Still, widespread 60s throughout the
area will foster one more day of weekend outdoor activities. Once
the front moves in Monday, highs will fall into the upper 50s to
lower 60s, but start to recover as quickly as Tuesday as most
lowland locations will nudge back upward into the lower to mid 60s.

18

.LONG TERM /WEDNESDAY THROUGH SATURDAY/...Deterministic and
ensemble solutions remain in sync, advertising another persistent
ridge over W WA throughout the remainder of the forecast period.
Temps throughout this period will continue to climb, starting off
in the mid to upper 60s for Wednesday...but it does not take too
long for 70s to start popping up in the area. These will be mostly
relegated to the SW interior Thursday but will spread out into
the majority of the interior lowlands both Friday and Saturday as
high temperatures range in the lower to mid 70s. This increase in
daytime highs will offset overnight lows somewhat, as they will
not be as brisk as they have been in the near term. Instead, they
will be more on the seasonable side, generally in the upper 40s to
lower 50s each night/early morning.

18

&&

.AVIATION...Upper level ridge nosing into Southern British Columbia
with an upper level low over Nevada giving the area northeasterly
flow aloft today. Low moves east tonight and ridge dissipates with
westerly flow aloft developing early Monday morning. In the lower
levels onshore flow continuing into Monday.

Satellite imagery shows fog and low clouds near the east side of the
Puget Sound, in the Snoqualmie, Snohomish, and Chehalis river valley
near Grays Harbor. The fog and low clouds are shallow and will
dissipate by 18-20z leaving clear skies across the area. Increasing
onshore gradients tonight into Monday morning with areas of MVFR
stratus along the coast around 09z and over the interior 14z-18z.


KSEA...Shallow stratus with LIFR ceilings and visibilities 3-5sm are
currently being observed at the terminal. The clouds should
dissipate by 18-20z leaving clear skies until MVFR stratus arrives
after 12z Monday morning. Winds light this morning becoming
northerly 4 to 8 knots midday. Winds turning southerly 4 to 8 knots
03z-06z. Felton/McMillian

&&

.MARINE...Surface high pressure over the waters today. Increasing
onshore flow tonight with a weak surface ridge ahead of the next
system to reach the area arriving Monday. The increasing onshore
flow will give the Central Strait of Juan de Fuca small craft
advisory westerlies tonight into early Monday morning, possibly not
strong enough to make it into the eastern sections of the strait.
Weak front moving through Monday with surface high pressure
rebuilding behind the front Monday night into Tuesday. The ridge
will remain into Thursday. Possibility of a thermally induced
surface trough moving up the coastline later Thursday into Friday.

Felton/McMillian

&&

.HYDROLOGY...No river flooding is expected through the next seven
days.

&&

.CLIMATE...The September monthly rain total for Seattle is 3.44
inches. This is the 10th wettest September since records started
at Seattle-Tacoma airport in 1945. A large percentage of that rain
fell in the last week of the month. The 2.59 inches in the last
week of September was the 3rd wettest last week of September at
Seattle-Tacoma airport surpassed only by 3.22 inches in 2013 and
2.89 inches in 1953.

The 2023 rain total at Seattle-Tacoma airport through the end of
September is 17.82 inches. This is the 8th driest total through
the first 9 months of the year and the driest since 17.37 inches
in 1994. Felton

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...None.
PZ...Small Craft Advisory from 6 PM this evening to 2 AM PDT Monday
     for Central U.S. Waters Strait Of Juan De Fuca.

&&

$$