585
FXUS66 KSEW 202142
AFDSEW

Area Forecast Discussion
National Weather Service Seattle WA
242 PM PDT Fri Sep 20 2024

.SYNOPSIS...Dry weather will continue Friday afternoon into
Saturday as high pressure moves through the region. A chance of
light rain will come via a disturbance on Sunday. The start of
next weeks work week will start dry as temperatures increase back
into the mid and upper 70s by Tuesday. A stronger cold front will
pass through Wednesday into Thursday, with increasing chances of
rain.

&&

.SHORT TERM /TONIGHT THROUGH MONDAY/...Yesterday`s upper level
trough over British Columbia has moved out of the region into
Montana/Saskatchewan today. A transient ridge has snuck in behind
this trough, which has in turn dried out western Washington with
cooler, and drier northwest air moving into the region. Cloud
cover has burned off from this morning`s light showers/drizzle
that took place between I-5 and US-2 in King/Snohomish Counties.
Some low level moisture has been sufficient enough for several
groups of cumulus clouds to remain. The clouds will stick around
into Saturday, and increase overnight with a weaker onshore push
filling in additional clouds for Saturday morning. Isolated areas
of patchy fog are possible in areas that do not get as much cloud
coverage.

Saturday will clear out to be the sunniest day of the weekend,
with any cloud coverage overhead burning off quickly Saturday
morning is drier air makes it way down towards the surface. This
will also increase temperature back into the upper 60s to low 70s
for highs (along with very light northwest winds).

The pattern shifts back to unsettled Sunday. A small/weak
shortwave trough is expected to pass over British Columbia Sunday.
Part of the trough is able to dig down into Washington, but
weakens as it becomes positively tilted due to a ridge building
behind it. The precipitation chances remain for Sunday, but have
dwindled in overall amounts. Lowland areas will most likely only
see a few hundredths of an inch of rain. This does increase
however going up towards Forks/Neah Bay, North Cascades, and Mt.
Vernon up into Bellingham. Anywhere from a quarter to a third of
an inch of rain is possible in these areas. Convection is not
expected with this activity.

Dry weather returns Monday as a ridge builds over the region,
tilting northeastward. This will clear out most cloud coverage
during the day, with temperatures still hovering in the upper 60s
to low 70s. Winds will turn light northeasterly to easterly
through the Cascades late Monday into Tuesday.

.LONG TERM /TUESDAY THROUGH FRIDAY/...The ridge on Monday will
continue to move inland on Tuesday, with flow aloft becoming more
southwesterly on Tuesday. With the winds becoming more offshore on
Tuesday, the temperatures will increase into the mid and upper 70s
during the day. HeatRisk will only rise to minor in lowland areas
(with potentially a couple isolated pockets of moderate in the
interior).

A trough is expected to follow the ridge, arriving by Wednesday
into Thursday and Friday. This will bring a cold front through,
decreasing temperatures into the upper 60s to low 70s. Rain
chances will increase across the entire coverage area with this
frontal passage. There appears to be at this time a better chance
of wetting rain with this system, especially in the north Cascades
and adjacent lowland areas. Some of the initial rain Wednesday may
be heavier. This system is still several days out, and will
be monitored for potential impacts due to possible heavier rain.

HPR

&&

.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...Generally light flow expected into Saturday as a surface
ridge expands over the Coastal Waters. The ridge will weaken on
Sunday as a frontal system moves onshore into British Columbia.
Ridging will build back into the area Monday into Tuesday for more
northerly and weakly offshore flow early next week. Onshore flow
then resumes the middle of next week with a frontal system moves
towards the area. Winds will continue to subside along the outer
Coastal Waters this evening. Otherwise, lighter winds expected over
the weekend.

Seas of 7 to 9 feet for the Coastal Waters will subside to 4 to 6
feet on Saturday, building to near 7 feet for the outer Coastal
Waters on Sunday. JD

&&

.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.

&&

$$