443
FXUS66 KSEW 292141
AFDSEW

Area Forecast Discussion
National Weather Service Seattle WA
241 PM PDT Sat Jun 29 2024

.SYNOPSIS...An approaching front will spread increasing clouds and
light precipitation across western Washington tonight through
early Sunday. The upper trough follows, with stronger onshore flow
and a possible convergence zone developing later Sunday. High
pressure will then begin to slowly but steadily strengthen onshore
early next week, before moving eastward late in the week. This
will maintain much warmer and dry conditions much of next week.

&&

.SHORT TERM /TONIGHT THROUGH TUESDAY/...Mild conditions with
increasing clouds across the region as the next front is pushing
onshore this afternoon. Expect rain to be generally limited
(largely less than a tenth of an inch) as the front breaks apart
into the interior, but locally higher amounts can be expected in
the mountains. With some instability over the Cascades, there
remains around a 10% chance of an isolated thunderstorm around Mt
Baker, but this remains a lower probability. Expect rather mild
temperatures overnight with widespread cloud cover and another
passing impulse through the upper trough will provide another
focus for showers early Sunday morning. Increasing onshore flow
will bring the potential for a Puget Sound Convergence Zone and
additional lingering mountain showers. Otherwise, the start of a
shift in the pattern will then emerge by Monday as a ridge begins
to amplify offshore. Initially, it`s far enough offshore that we
maintain light onshore low-level flow. This will keep temperatures
on a warming trend, but only gradually so, and maintain
widespread morning clouds each day. By Tuesday night, this onshore
flow will begin to weaken.

.LONG TERM /WEDNESDAY THROUGH SATURDAY/...Confidence continues to
be higher with respect to a strengthening ridge that will likely
dominate the pattern across the Pacific NW through much of next
week. While there are a small subset of ensemble members (15% or
so) that would suggest the potential for a trough to sweep through
the region by Friday, the majority feature a ridge somewhere in
the neighborhood of the region. While the finer details of where
the ridge axis set up may determine the details of just how warm
it gets (and if we can pivot around to offshore low-level flow at
any point), confidence is increasing for a steady ramp-up in
temperatures late in the week. Temperatures near or slightly above
normal Wednesday will likely climb to 10-15 degrees above normal
late in the week. For now, this would correlate to temperatures in
the 80s to around 90 and moderate HeatRisk developing Thursday
through Saturday. Along with the potential for increasing heat,
this warming and drying trend would lead to a potential increase
in fire weather concerns around and after the Independence Day
holiday.                                     Cullen

&&

.AVIATION...Flow aloft is becoming southwesterly ahead of a
shortwave trough approaching from the west today (ridging also
located east of the Cascades). A weak front has begun to produce
showers along the coast and the southwest interior. Activity is
moving in a north-northeast direction. Additional showers may fire
this afternoon along the Cascade Crest and in Puget Sound. The
threat for thunder is very low, but heavy showers may reduce
CIGs/VIS temporarily and create variable winds. Winds remain
variably out of the west, but will solidify out of the south this
evening as the trough approaches (6 to 10 kt).

High VFR ceiling deck has filled in ahead of the system, and CIGs
will gradually lower to widespread MVFR late this evening/Sunday
morning. There are increasing chances for IFR/LIFR CIGs/VIS in the
form of low clouds/fog Sunday morning, mainly for terminals west of
I-5. All ceilings/fog will mostly clear late Sunday
morning/afternoon (except for potentially the coast).

KSEA...Chance of showers this afternoon (between 02-07Z) from the
south. If a heavy shower passes over the terminal, may briefly drop
CIGs/VIS to instrumental meteorological conditions. West winds 6 to
8 kt will become southerly early this evening ahead of the front.
Increasing chance for impactful IFR/LIFR CIGs/VIS Sunday morning
before scattering out.

HPR

&&

.MARINE...Trough/frontal system is positioned over the coastal
waters this afternoon, and will continue to move inland today into
tonight. Showers are moving along the coast, with a few heavier
showers possible in some of the inner waterways. Widespread low
marine clouds/fog is possible Sunday morning, especially off the
coast and in the eastern Strait of Juan de Fuca. The visibilities
may drop below a quarter of a mile at times.

Pushes down the Strait of Juan de Fuca are expected with high
pressure building offshore early next week. The push Sunday
afternoon is expected to peak at around 20 kt in the central/east
sections, with the Monday evening push expected to exceed this.
Strong northwesterlies over the coastal waters may also exceed 20 kt
Tuesday into Thursday.

Seas will reach 4 to 6 feet today, and may increase to 6 to 8 feet
in the outer coastal waters Wednesday and Thursday.

HPR

&&

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

$$