143
FXUS66 KSEW 290950
AFDSEW

Area Forecast Discussion
National Weather Service Seattle WA
250 AM PDT Wed May 29 2024

.SYNOPSIS...Scattered showers with embedded thunder possible
across western Washington today. Weak high pressure will move
across the region Thursday and Friday with warmer and drier
conditions. A parade of frontal systems look to impact the Pacific
Northwest late Saturday through the early portion of next week
bringing additional rounds of wet and unsettled conditions.

&&

.SHORT TERM /TODAY THROUGH FRIDAY/...An upper level trough is
currently traversing western Washington this morning, already
kicking off a few convective showers along the coast and just
offshore thanks to anomalously cold air aloft (500 mb heights
nearly down to -25C). Meanwhile, a weak area of showers associated
with the Puget Sound Convergence Zone (PSCZ) are streaming
northeast from Everett through Granite Falls and to Darrington in
Snohomish County.

Weak instability will develop into this afternoon thanks to the
upper-level trough overhead with maximum SB CAPE to around 200 to
250 J/kg this afternoon and evening. HREF member consensus brings
scattered showers and downpours onshore through this morning into
the Puget Sound Lowlands into the late morning and early afternoon
with showers and isolated thunderstorms lingering longest with
the PSCZ over King County from around 2 PM onward through this
afternoon and early evening. Primary hazards with showers and
thunderstorms today will be small hail, isolated lightning
strikes, and brief gusty winds. Highs today in the upper 50s to
low 60s.

Quiet weather Thursday and Friday as a shortwave ridge builds
across the Pacific Northwest ahead of the next incoming shortwave
trough and associated frontal system. While we see warming and
drier conditions, highs only climb back to seasonal normals for
the end of May in the upper 60s/near 70 by Friday. Mostly dry
conditions as we close out the workweek, though cannot rule out an
isolated shower across the North Cascades. Overnight lows remain
chilly for this time of the year in the low 40s to even upper 30s
for portions of the Southwest Interior.

.LONG TERM /SATURDAY THROUGH TUESDAY/...Long range ensembles and
deterministic NBM forecasts continue to favor cool and unsettled
weather, especially Sunday through Tuesday with NBM forecast high
temperatures dropping up to 5 degrees from last night`s forecast
as ensemble clusters support a further east progression of our
late-week ridge now further into the Great Plains and stronger
shortwave energy ejecting out of the vertically-stacked low over
the Gulf of Alaska. Highs remain seasonably cool in the low to
mid 60s with snow levels well above pass level.

With a train of shortwave troughs and frontal systems poised to
parade across the Pacific Northwest Sunday through the middle of
next week, this will lead to several periods of moderate rainfall.
Heaviest rainfall looks to focus across the western Olympic
Peninsula and across the western Cascades with an 80% chance for
3-day liquid precipitation totals of at least 2 inches in the
Sunday-Tuesday night timeframe and a 60% chance for 3-day totals
of at least 3 inches focused across the southwestern Olympics and
central Cascades. While no river flooding is currently forecast, a
handful of rivers (Skokomish, Snohomish, and Skykomish) are now
forecast to rise into or near Action Stage Monday and Tuesday.

Davis

&&

.AVIATION...An upper level trough axis over the region early
this morning will shift eastward today with the flow aloft becoming
northwesterly. The air mass is moist and will become somewhat
unstable this afternoon. MVFR ceilings...especially around Puget
Sound...will persist through midday before lifting to lower end VFR
this afternoon and evening. Scattered showers and isolated afternoon
thunderstorms are expected across the area as an upper trough
remains in the vicinity. Another convergence zone is expected to
form over south Snohomish and King Counties near or after 20Z.

KSEA...MVFR ceilings lifting to VFR 20z-22z. Surface winds S/SW 5 to
10 knots rising to 12 to 18 knots by around 20Z. Winds are expected
to veer to N/NW with the the convergence zone 22Z-03Z before backing
again to S/SE late this evening.

27

&&

.MARINE...A surface ridge will build into the coastal and offshore
waters today maintaining onshore flow. The ridge will weaken later
Friday as another weak front approaches offshore then drags onshore
on Saturday. A stronger front will follow on Sunday with a higher
probability of headlines for the coastal waters and portions of the
inland waters.

27

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...None.
PZ...Small Craft Advisory from 2 PM this afternoon to 2 AM PDT
     Thursday for Central U.S. Waters Strait Of Juan De Fuca-
     East Entrance U.S. Waters Strait Of Juan De Fuca.

&&

$$