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035
FXUS66 KSEW 160922
AFDSEW

Area Forecast Discussion
National Weather Service Seattle WA
222 AM PDT Sun Jun 16 2024

.SYNOPSIS...
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Showers and isolated thunderstorms will continue today
as an upper level trough remains over the region. The trough will
shift east on Monday with lingering showers over higher terrain. A
warming and drying trend will commence for the remainder of the
week as high pressure aloft gradually builds into the region.
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.SHORT TERM /TODAY THROUGH TUESDAY/...
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As of 2 AM PDT, convergence
zone showers between Snohomish and Stevens Pass are slowly
tapering off. Rain rates have lessened with these showers, and the
Flash Flood Watch for the Bolt Creek burn scar has been allowed
to expire. Alongside the convergence zone activity, light showers
along the coast will continue to progress inland with onshore flow
while showers just north of the Canada border continue to shift
southward with an advancing front.

An upper level trough will slowly drop southward throughout the
day today, swinging a frontal system across western Washington.
Another round of showers will spread southward throughout the day
with embedded thunderstorm activity mainly southwest of the Puget
Sound, where models show instability peaking around 250-300 J/kg
in the early afternoon. Storms that develop may produce small
hail, locally heavy rain, and gusty outflow winds alongside
lightning. The primary push of moisture will taper off by this
evening, with another round of showers mainly over higher terrain
moving southward across western Washington early Monday morning as
a disturbance in the northerly flow aloft ripples through.
Conditions will dry out for most areas on Monday, except for
light showers favored to linger over the North Cascades. Another
shortwave trough will drop across the Pacific Northwest early
Tuesday, stirring up more light shower activity once again
favored over the mountains. Temperatures will remain on the cool
side in the mid 60s today and Monday before returning to near-
normal around 70 degrees by Tuesday.

.LONG TERM /WEDNESDAY THROUGH SATURDAY/...Ensembles continue to
highlight weak flow through the extended period with a warming
trend through at least mid-week. Onshore flow will keep coastal
areas cool while lowlands further inland are on track to reach 80
degrees by Thursday. Temperatures will slowly moderate thereafter
with mostly dry conditions through the period.

Lindeman
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.AVIATION...
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A broad upper level trough remains over the Pac NW with
a cool and slightly unstable air mass over western WA. As the upper
level low continues to move south and east throughout the day, flow
aloft will be variable for much of the day before turning to the
northeast by tonight and becoming more northerly Monday.

Latest radar still shows some isolated showers, but much of W WA is
dry. The notable standout is a convergence zone along the
Snohomish/King county line, but this is well east of any terminals
and should not have a significant impact on aviation operations.
With the upper level low still above the area, expectation is for
scattered showers to develop again late this morning and into the
afternoon and evening. Conditions are more stable than yesterday, so
thunder chances are less. While cannot rule out a stray rumble,
confidence is not there for inclusion in any TAFs.

VFR conditions in place for much of the area, however terminals
along the east Sound seeing MVFR cigs due to abundant low level
moisture and will likely remain that way into the late morning
before improving back to VFR. CLM looks like it may also fall down
into MVFR after 12Z, while remaining western terminals trending to
remain VFR as per latest data, but would not hurt to monitor, as HQM
and OLM typically experience low cigs.

Surface winds south/westerly at 8 to 12 kt will become northerly by
Sunday afternoon at 4 to 8 kt.

KSEA...Cigs lowered a little ahead of schedule with MVFR conditions
in place this early morning and will likely stay that way til around
18Z. Still a little instability expected this afternoon, which will
give cigs a boost but will also carry shower chances. PoPs remain
low and does not look to be enough instability to warrant any
thunder mention in the forecast. Surface wind discussion immediately
above this section applies.

18
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.MARINE...
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Onshore flow will continue as high pressure over the NE
Pacific will maintain light to moderate winds over W WA through next
week. At this time, flow over the next 24 hours looks light enough
to not meet any headline criteria at this time, however, winds could
reach 15-20 kts this evening through late tonight in the outer
coastal waters and central and eastern portions of the Strait.

Seas generally 4 to 6 feet for much of today before increasing to 6
to 8 feet tonight. These will ease throughout the day Monday,
getting back to 4 to 6 feet by Monday evening.

18
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.SEW WATCHES/WARNINGS/ADVISORIES...
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WA...None.
PZ...None.
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$$