322
FXUS66 KSEW 220354
AFDSEW

Area Forecast Discussion
National Weather Service Seattle WA
854 PM PDT Tue May 21 2024

.SYNOPSIS...A cold front continues to move across western
Washington this evening, pushing most of the rainfall east of the
Cascades. Surface high pressure will bring a short reprieve in
precipitation Wednesday night and Thursday before another system
swings through Friday and Saturday. Remainder of the weekend into
next week appears unsettled with multiple chances of showers.
Temperatures look to warm early next week as a ridge of high
pressure builds across the Pacific Northwest.

&&

.SHORT TERM /TONIGHT THROUGH FRIDAY/...A late-season closed 500 mb
low and attendant frontal system continue to move across western
Washington this evening, though widespread stratiform rain is
pushing east of the Cascades as the front moves onshore.
Otherwise, a damp and breezy night with showers and drizzle,
mostly favoring areas of southern Snohomish and northern King
Counties thanks to the development of a Puget Sound Convergence
Zone. QPF/rainfall totals will range from a few tenths to half an
inch in Puget Sound/lowlands under the PSCZ. Lows tonight remain
on the cool side in the low to mid 40s.

An upper level ridge will sneak behind the upper level trough
Wednesday-Thursday. This will dry out a majority of the coverage
area (minus some lingering showers in the Cascades). A few cloud
breaks are possible Wednesday afternoon, as well as into Thursday.
The next shortwave trough/cold front from Canada approaches
Washington Friday, with a return chance of showers. Snow
levels/freezing levels will drop down to 3,500 feet with this
system, and will cooler air aloft, there will be a conditional
chance with thunder with this system, from King County northwards
to the Canadian border.

High temperatures will increase from the mid 50s Tuesday, to the
low and mid 60s Wednesday into Friday. Lows will range from the
low to upper 40s. Breezy winds of 10 to 15 mph (gustiest winds
near the Strait of Juan de Fuca) out the southwest Tuesday, will
diminish to around 5 to 10 mph southwesterlies Wednesday into
Friday.

.LONG TERM /SATURDAY THROUGH TUESDAY/...A little bit of
disagreement still exists this weekend into next week, but most
ensembles/deterministic models point to unsettled weather
continuing into the long term. A quick ridge may dry out parts of
the region Saturday night/Sunday, but shower chances will continue
this weekend into next week. High temperatures start to approach
the low 70s by Monday/Tuesday, with lows also increasing into the
low 50s. Winds remain light out of the south.

Davis/HPR

&&

.AVIATION...Widespread low ceilings across western Washington this
evening, ranging from MVFR to IFR with some localized LIFR
conditions as a frontal system makes its way across the region. Rain
showers are ending region-wide, but will likely continue through the
afternoon through the north interior as well as around KPAE as a
convergence zone develops overnight. Visibility has largely improved
with decreasing shower coverage. Ceilings may temporarily lift to
MVFR to even low-end VFR immediately behind the front, but should
decrease again late overnight into early tomorrow morning with the
airmass being moist, as well as under the convergence zone. Cloud
cover should decrease over the area during the day tomorrow,
allowing a return to VFR conditions. The marine layer looks to keep
the coast with low ceilings. Breezy south/southwesterly winds
continue through the evening and will ease tomorrow.

KSEA...MVFR conditions with light rain, easing this evening.
Ceilings may lift a bit around midnight but look to decrease as the
convergence zone develops to the northeast of the terminal. VFR
conditions return late tomorrow morning as cloud cover decreases.
S/SW winds 10-15 kt with occasional gusts to 20 kt easing down to 5
to 10 kt tomorrow.

LH

&&

.MARINE...A frontal system continues to move inland this evening,
with strong post-frontal winds. Upgraded the Small Craft Advisory
to a Gale Warning for the northern offshore waters given current
observations and forecast trends. Small Craft Advisories in effect
most elsewhere for elevated winds and seas. Seas will rise above
10 ft across the offshore waters overnight and continue rise to as
high as 16 ft by Wednesday especially over the northern coastal
zones. Waves will be steep with short period waves dominating.
Another frontal system may pass through area waters on Friday,
bringing elevated seas and breezy winds.

Davis/Cook

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...None.
PZ...Small Craft Advisory until 5 PM PDT Wednesday for Grays Harbor
     Bar.

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

     Small Craft Advisory until 5 PM PDT Wednesday for Coastal Waters
     From Cape Flattery To James Island Out 10 Nm-Coastal Waters
     From James Island To Point Grenville Out 10 Nm-Coastal
     Waters From Point Grenville To Cape Shoalwater Out 10 Nm.

     Gale Warning until 11 AM PDT Wednesday for Coastal Waters From
     Cape Flattery To James Island 10 To 60 Nm-Coastal Waters
     From James Island To Point Grenville 10 To 60 Nm.

     Small Craft Advisory until 8 PM PDT Wednesday for Coastal Waters
     From Point Grenville To Cape Shoalwater 10 To 60 Nm.

&&

$$