396
FXUS66 KSEW 282208
AFDSEW

Area Forecast Discussion
National Weather Service Seattle WA
308 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/...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/...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...West-southwest flow as upper-troughing continues. As
above so below, southwest winds are occuring at the surface with
gusts up to 20-25 kts being observed at a number of terminals. VFR
trending so far this afternoon. However, more widespread MVFR CIGs
are set to return tonight with localized IFR possible at times.
Showers are to remain tonight as well along with a convergence zone
forming in the vicinity of KPAE and KAWO before meandering
southward. Showers are to continue into Monday also with VFR
returning around midday.

KSEA...It has been a mix of VFR/MVFR conditions so far today. CIGs
have been around 3,500-4,500 but passing showers have done enough to
bring down CIGs to around 2,500-3,000 ft at times. For tonight, 50-
60% chance of MVFR trending most hours with continued showers. Winds
are to remain out of the SW between 8 to 12 kts with gusts up to 20
kts but gusts should ease into the early morning hours on Monday.
Convergence zone activity late tonight may slow improvement back to
VFR until Monday afternoon.


McMillian

&&

.MARINE...Another active day across area waters with a host of SCA
out. Puget Sound and Northern Inland waters will continue before
conditions subside this evening. However, the central and eastern
strait along with coastal waters where seas are around 9 to 10 ft,
will persist into Monday morning. Scattered showers along with an
isolated chance for thunderstorms are in the offing this afternoon
and Monday afternoon. An additional disturbance looks to arrive
Monday night into Tuesday but some uncertainty remains on winds.

Seas remain elevated through Tuesday from 8 to 10 feet followed by a
gradual decrease to 4 to 6 feet later in the week.

McMillian

&&

.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.

&&

$$