423
FXUS66 KSEW 291547
AFDSEW

Area Forecast Discussion
National Weather Service Seattle WA
847 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/...No major updates to the
forecast this morning. Shower and isolated heavy rain is occuring
across the San Juan Islands and along the coast. The rest of the
previous discussion will follow.

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, with small pockets of
IFR/LIFR (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, which will track southeast. Possibility
exists for lightning, wind shifts/gusty winds and small hail.

KSEA...Intermittent MVFR/VFR ceilings (with vicinity showers)
lifting to low-end 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. Vicinity thunder is possible this
afternoon, but confidence in location/timing is too low to put in
the TAF at this time.

27/HPR


&&

.MARINE...A surface ridge will build into the coastal and offshore
waters today maintaining onshore flow. A strong push of westerlies
will push in the Strait of Juan de Fuca today (small craft advisory
remains in effect). 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/HPR


&&

.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.

&&

$$