000
FXUS66 KSEW 290355
AFDSEW

Area Forecast Discussion
National Weather Service Seattle WA
858 PM PDT Sun Apr 28 2024

.SYNOPSIS...Unsettled, cool weather continues with a series of
frontal systems crossing the region through the middle of the
week. A brief warming and drying is expected midweek before
conditions turn unsettled again late week.

&&

.SHORT TERM /TONIGHT THROUGH WEDNESDAY/...Showers associated with an
upper level trough over the area continue as per latest radar loop.
The strongest echoes are occurring over portions of the north Sound
as well as western Skagit and Snohomish counties. Current IR
satellite imagery does an excellent job of highlighting the PSCZ
nature of this increased activity. What will be interesting to see
is how precip amounts will be impacted as this feature starts to
bleed eastward over the Cascades. The timing for this still seems to
be on track with the overnight hours and thusly falling under the
purview of the inherited Winter Weather Advisory...which, having
said all this...looks to be in good shape with no need for
alteration or updating.

Soggy though it may be, forecast is holding true and as such no need
for any evening updates to public products at this time. For
additional forecast details, please refer to the Previous Discussion
section below.

From Previous Discussion...Scattered showers continue to spread
onshore across Western Washington this afternoon as an upper trough
west of Haida Gwaii digs southward toward the region. Cooling
temperatures aloft will lead to increasing instability late today
into Monday for a chance of thunderstorms as well as snow levels
dipping to most pass levels late tonight. A Winter Weather Advisory
continues for the Cascades above 3500 feet late tonight into Monday
morning. Another upper trough digs southward across the area Monday
night into early Tuesday. The focus with that system continues to be
a bit further southward...with much of the QPF from the Seattle area
southward.

The trough axis shifts east of the area by late Tuesday afternoon
as drier north-northwest flow aloft develops ahead of a weak upper
ridge offshore. As things presently stand, Wednesday is shaping up
to be one of the nicest days of the week as weak ridging aloft
leads to mostly dry conditions, some sunshine, and high
temperatures bouncing back to near seasonal norms.

.LONG TERM /THURSDAY THROUGH SUNDAY/...From Previous
Discussion...The woes of deciphering the extended portion of the
forecast continue. There is general agreement that another upper
trough crossing southern British Columbia on Thursday will bring a
returning chance of showers. Uncertainty in the forecast for Friday
into next weekend increases by the day. The Euro ensembles favor
additional troughing and cool temperatures while the more optimistic
GFS ensemble mean has weak upper ridging and temperatures climbing a
little above normal. The NBM 10th and 90th percentile high
temperature forecasts have a 10 to 15 degree spread by Friday and
Saturday. Given these levels of uncertainty, near climo temps and a
generic chance of showers forecast late in the week is the best
forecast at this stage. 27

&&

.AVIATION...An upper trough continues to advance across the
region, maintaining onshore low-level flow and fairly widespread
showers. Gusty surface winds continue around many area terminals,
and expect this to continue in the unstable and showery pattern
tonight through early Monday. Expect a lingering convergence zone
across southern Snohomish County to fade out, and unlikely to reach
the primary King County terminals. Ceilings likely to remain a mix
overnight, with areas under showers (or persistent clearing) likely
to dip lower into the low MVFR or locally IFR range, while most
remaining in MVFR or low VFR through the balance of the night. Trend
back to VFR conditions likely again tomorrow with again scattered
showers and gusty surface winds.

KSEA...Expect continued VFR ceilings and southerly surface winds
this evening with any convergence remaining focused well north of
the terminal. Showers will remain over/near the terminal area
overnight with gusty southerly surface winds. Guidance suggest
settling to MVFR again overnight through around daybreak, but a
return to VFR on Monday through the day.

&&

.MARINE...Yet another disturbance continues to maintain gusty
advisory strength winds through the central and eastern Strait of
Juan de Fuca and into the adjacent interior waters this evening.
Meanwhile, seas holding around 9 to 10 ft with a dominant period
around 10 seconds will maintain rather steep conditions over the
coastal waters tonight. While winds are expected to gradually trend
down, the potential for localized gusts to 25-30 kt under strong
showers or isolated thunderstorms will continue into Monday. Another
front arrives Monday night into Tuesday for another round of more
widespread advisory strength winds. Seas across the coastal waters
will generally remain near or just below 10 ft through the next
couple of days, before subsiding more significantly toward midweek.

&&

.HYDROLOGY...No river flooding is anticipated over the next seven
days.


&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...Winter Weather Advisory from 11 PM this evening to 11 AM PDT
     Monday for West Slopes North Cascades and Passes-West
     Slopes North Central Cascades and Passes-West Slopes South
     Central Cascades and Passes.

PZ...Small Craft Advisory until 5 AM PDT Monday for Central U.S.
     Waters Strait Of Juan De Fuca-East Entrance U.S. Waters
     Strait Of Juan De Fuca.

     Small Craft Advisory until 11 PM PDT this evening for Northern
     Inland Waters Including The San Juan Islands.

     Small Craft Advisory until 8 PM PDT this evening for Puget Sound
     and Hood Canal.

&&

$$