735
FXUS66 KSEW 201600
AFDSEW

Area Forecast Discussion
National Weather Service Seattle WA
900 AM PDT Fri Sep 20 2024

.SYNOPSIS...Mainly dry weather today and Saturday. Rain spreads
inland on Sunday for a chance of rain over the coast, north part
and mountains. High pressure brings warmer weather moving into
Tuesday. Rain returns by midweek with wet and cooler weather
toward next weekend.

&&

.UPDATE...No major changes to the forecast below. Drizzle
activity between I-90 and US-2 in King/Snohomish Counties is
diminishing this morning. Cloud cover is still expected to clear
out later this morning and afternoon, revealing mostly sunny to
partly cloudy skies. High temperatures will remain cool with highs
in the mid 50s to mid 60s. Please see discussion below for
further details.

HPR

&&

.SHORT TERM /TODAY THROUGH SUNDAY/...We`re under NW flow today
with a ridge over the NE Pacific and a trough over western Canada.
We may see isolated showers in the interior and Cascades today
but otherwise looking mainly dry. Temperatures will continue to
track cooler than average and in the 60s.

The next frontal system stalls over southern B.C. on Saturday,
leaving western WA dry and mild. The air mass over western WA is a
little warmer with temperatures closer to average. Rain spreads
into western WA on Sunday but mainly impacting the coast, north
part near the border, and north/central Cascades. Precipitation
from Seattle south is light (trace to a few hundredths if
anything). 33

.LONG TERM /MONDAY THROUGH THURSDAY/...Light showers linger on
Monday with warmer and drier weather on Tuesday with high
pressure. Temperatures on Tuesday reach the 70s with a few low 80s
possible. Wetter weather returns toward midweek as the ridge
shifts east and moist S/SW flow sets up over western WA. We`re
back to a troughing pattern moving toward the end of the week for
additional showers and cooler weather. 33

&&

.AVIATION...Northwest flow aloft continues through today as weak
upper ridging builds into the area. Low level onshore flow will
become light northerly this afternoon. A mix of MVFR and areas of
IFR this morning across portions of southern and central Puget
Sound. Otherwise, VFR elsewhere across Western Washington. Stratus
will slowly lift and scatter later this morning into the afternoon.
VFR high clouds then expected later this afternoon and evening.
Patchy fog and stratus may develop early Saturday morning,
especially along the coast, and southern Puget Sound near KOLM.
Light winds this morning will become light north this afternoon.

KSEA...MVFR cigs will continue through approximately midday (19-
20z), slowly lifting to VFR and scattering this afternoon. VFR high
clouds around this evening. The probabilities of stratus developing
Saturday morning around the terminal are lower, generally around 20%
of IFR cigs. Light southerly winds this morning will slowly
transition to north this afternoon and NE tonight. JD

&&

.MARINE...Onshore flow will gradually relax today as a weak
surface low in the vicinity of Tofino dissipates and a surface
ridge offshore expands in the coastal waters. The ridge will
remain in place into Saturday, but weaken on Sunday as a frontal
system moves onshore over southern British Columbia. No headlines
are anticipated with this. Thermally induced low pressure
expanding northward along the Oregon coast Monday into Tuesday
will turn the flow more northerly or weakly offshore. Onshore flow
resumes by the middle of the coming week as a weakening frontal
system approaches the area. 27

&&

.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 James Island To Point Grenville 10 To
     60 Nm-Coastal Waters From Point Grenville To Cape
     Shoalwater 10 To 60 Nm.

&&

$$