106
FXUS66 KSEW 212155
AFDSEW

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

.SYNOPSIS...A cold front and associated upper level trough
continues to bring rain across Western Washington this afternoon,
with activity wrapping up by Wednesday morning. A quick ridge will
dry the region out 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. High temperatures will climb from the fifties and
sixties, to the low seventies by next week.

&&

.SHORT TERM /TONIGHT THROUGH FRIDAY/...Late season winter-style
shortwave trough continues to advance southward from B.C. Canada
into Washington this afternoon and evening. A jet max sits on the
leeward side of the low, feeding some moisture into Washington.
This moisture will start to shut off once the low reaches into the
state by late tonight/Wednesday morning.

Radar continues to show rain falling over much of western
Washington this afternoon. The heaviest of the rain is shifting
more from the coast/Olympics this morning, over into Puget
Sound/Cascades this afternoon. Tonight into Wednesday: the rain
will taper back to showers (although a convergence zone is
possible once the cold front swings through Snohomish County).
QPF/rainfall totals will range from around a half an inch in Puget
Sound/lowlands, to around an inch in the Olympics/coast, and
amounts exceeding 1-2 inches in the Cascades. River and urban
flooding impacts are not expected.

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.

HPR

&&

.AVIATION...Pretty widespread IFR conditions with light rain
especially through the interior TAF locations. Conditions are
expected to improve during the the evening, with post-frontal
convergence zone showers possible late Tuesday evening. The most
likely scenario is that the convergence zone - if it develops to
remain north of KBFI. Southerly flow 5-15 kt over the interior with
west to southwest winds increasing to 10-20 kt with gusts to 25 kt
along the coast and strait - KHQM/KCLM.

KSEA...IFR conditions with light rain, with rain easing by 22/04z
and some improvement in ceilings and vis. Convergence zone is
expected to stay north of KSEA/KBFI. S/SW winds 10-15 kt with gusts
to 20 kt remaining elevated into Wed morning with lower/MVFR
ceilings persisting.

&&

.MARINE...A strong frontal system crossing area waters, boosting
winds and seas to SCA levels over the coastal waters and through the
Strait of Juan de Fuca into Wednesday. 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.

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...None.
PZ...Small Craft Advisory from 8 PM this evening to 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 from 8 PM this evening to 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.

     Small Craft Advisory from 5 PM this afternoon to 8 PM 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-Coastal Waters From Point
     Grenville To Cape Shoalwater 10 To 60 Nm.

&&

$$