201
FXUS66 KSEW 290359
AFDSEW

Area Forecast Discussion
National Weather Service Seattle WA
859 PM PDT Tue May 28 2024

.UPDATE...Radar and satellite imagery show the well defined
convergence zone over Island and Snohomish County which will
continue through the overnight hours tonight. Elsewhere, a few
light scattered showers will pass across the region. Shower
activity will increase tomorrow as the upper-level trough axis
passes through western Washington. Lapse rates tomorrow continue
to show support for the potential of a few lightning strikes this
afternoon, with the best chances along the Pacific Coast tomorrow
morning and with the convergence zone that develops tomorrow
afternoon and evening, which looks sink southward toward King
County.

LH

&&

.SYNOPSIS...A convergence zone east of the Puget Sound will
continue this evening with scattered showers and perhaps a few
lightning strikes elsewhere across the region tonight into
Wednesday. A shortwave ridge and surface high to the south will
bring warmer and drier conditions for the rest of the week. A
series of systems will cross the Pacific Northwest over the
weekend and into early next week, bringing more rounds of wet
weather.

&&

.SHORT TERM /TONIGHT THROUGH SATURDAY/...Stratiform rain spreading
inland will continue to destabilize this afternoon and transition
to showers. Skies will stay mostly cloudy today, limiting high
temperatures to the 50s for most areas. While mean model
instability is fairly limited at 100 J/kg or less, a lightning
strike cannot be ruled out this afternoon. Confidence is high
that convergence zone activity will form this evening over the
Puget Sound which will slowly propagate eastward, lingering
through the early morning hours on Wednesday. Short range
ensembles keep most of the PSCZ shower activity north of Stevens
Pass before dissipating. More post-frontal showers will spread
inland on Wednesday as an upper level trough axis passes overhead,
and models continue to show another round of PSCZ showers
developing in the evening. A few lightning strikes are possible
once again on Wednesday afternoon in any stronger showers that
develop, with slightly more instability available. Temperatures
will peak a couple degrees higher on Wednesday, closer to 60
degrees for most areas.

High pressure will build inland on Thursday and Friday, allowing
conditions to dry out. Any lingering showers will be limited to
the northern Olympic Peninsula and North Cascades. Temperatures
will warm towards the end of the week, reaching a degree or two
below normal by Friday in the mid to upper 60s for most lowland
locations.

.LONG TERM /SUNDAY THROUGH WEDNESDAY/...Ensembles show good
agreement that cooler and wetter conditions will return throughout
the long term. A weak shortwave trough is on track to move across
the region on Saturday, cooling temperatures off a few degrees
and bringing in scattered showers. The region will have little
time to dry out with a series of deeper storm systems following
close behind. Long range ensembles continue to show much wetter
conditions entering the region Sunday through Tuesday, especially
over the western Olympic Peninsula and Cascades, where up to 4
inches of rainfall is currently forecast to fall over the span of
three days. However, models continue to show a wide range of
possible solutions with GFS precipitation amounts nearly double
that of the ECWMF. Uncertainty remains in terms of rainfall totals
and the placement of heaviest rainfall through the period.
Temperatures will return to near- normal with highs in the low to
mid 60s through the weekend and into early next week.

Lindeman

&&

.AVIATION...Upper level trough axis moving east of the are
tonight. Southwesterly flow aloft becoming northwesterly behind
trough axis. Northwesterly flow aloft continuing through
Wednesday. Onshore flow in the lower levels easing Wednesday. Air
mass moist and somewhat unstable Wednesday afternoon.

Convergence zone over Snohomish county continuing until around 09z
with IFR ceilings. For the remainder of the area VFR ceilings. All
areas ceilings lowering to MVFR 12z-15z with an slow improvement
trend midday lifting the ceilings back up to the low end of VFR.
Air mass somewhat unstable Wednesday afternoon with isolated
thunderstorms.

KSEA...VFR ceilings lowering to MVFR 12z-15z. Ceilings lifting
back up to VFR 19z-22z. Thunderstorm chance not high enough to put
in terminal forecast. Light and variable winds becoming southerly
4 to 8 knots by 08z. Southerly winds becoming southwesterly and
increasing to 10 to 15 knots around 19z.

Felton

&&

.MARINE...Onshore flow tonight easing a little Wednesday. Small
craft advisory westerlies in the Central and Eastern Strait will
ease after midnight. A similar westerly push in the Strait is
expected Wednesday night into Thursday morning. Onshore flow
continuing into the weekend. Waves 4 to 6 ft through the period.

Felton

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...None.
PZ...Small Craft Advisory until 2 AM PDT Wednesday for Central U.S.
     Waters Strait Of Juan De Fuca-East Entrance U.S. Waters
     Strait Of Juan De Fuca.

&&

$$