867
FXUS66 KSEW 210213
AFDSEW

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

.SYNOPSIS...Dry weather will continue 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 TUESDAY/...No major changes have been
made this evening. The rest of the previous discussion can be
found below with some timing changes. An updated aviation and
marine section have been provided.

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 /WEDNESDAY THROUGH SATURDAY/...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 tonight into much of
Saturday before turning more zonal as a weak upper level ridge
starts to flatten out. Light and variable surface winds at the time
of this writing are expected to continue for most terminals
overnight and into Saturday morning. Locations that do see a slight
increase in wind speed...yet still less than 5 kts...will see the
direction shift northerly. Remaining sites will join in that
direction by Saturday afternoon.

VFR conditions in place over much of W WA with an isolated case of
MVFR conditions over central Pierce county. While most terminals may
see some FEW to SCT low clouds...and thus remain VFR
overnight...locations that typically tend toward lower cigs, such as
OLM and PWT, will see MVFR to IFR conditions emerge by 12Z.
Widespread VFR conditions expected to return by late Saturday
morning.

KSEA...VFR conditions with high clouds at times tonight into
Saturday. Patchy fog and stratus may develop into localized areas of
Puget Sound on Saturday morning, and while FEW to SCT low clouds are
possible, lower cigs are not expected over the terminal. Light and
variable winds early this evening before slowly transitioning to
northerly tonight and for the remainder of the TAF period.

18


&&

.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/18



&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...None.
PZ...None.
&&

$$