163
FXUS66 KSEW 192136
AFDSEW

Area Forecast Discussion
National Weather Service Seattle WA
236 PM PDT Sun May 19 2024

.SYNOPSIS...An upper level trough will continue to move east out
of the region this afternoon. Weak upper level ridging will then
nudge into the region for warmer and drier conditions on Monday.
Another trough will drop south into western Washington from
British Columbia on Tuesday and Wednesday for a return to cooler
and unsettled weather. A brief dry break is possible on Thursday,
before cool and unsettled conditions return Friday and persist
into the start of the weekend.

&&

.SHORT TERM /TONIGHT THROUGH WEDNESDAY/...An upper level trough
over the region will continue to progress eastward tonight. Radar
this afternoon shows scattered showers across much of western
Washington. A few lightning strikes have been observed with cells
in Grays Harbor County this afternoon. While not widespread, cannot
rule out additional isolated lightning strikes through the remainder
of the afternoon. Small hail, gusty winds, and brief heavy downpours
will be possible in the vicinity of any storms that do develop.
Expect showers to gradually taper tonight into Monday as upper
level ridging starts to nudge into the area from the NE Pacific.
High temperatures across the region this afternoon will generally
top out in the upper 50s to low 60s today.

Weak upper level ridging nudging into the area will bring drier
and warmer conditions to the region on Monday. Morning stratus and
some areas of patchy fog will scatter out for some afternoon sun.
High temperatures will approach seasonal norms - generally
topping out in the mid 60s across the interior. Highs along the
coast will stay cooler, generally topping out in the upper 50s to
low 60s.

The next upper level trough will drop south from British Columbia
Tuesday into Wednesday. At the surface, a cold front moving into
the region on Tuesday will bring the next chance of more widespread
precipitation for western Washington. This system continues to
look rather wet for May, with much of the lowlands expected to
pick up about a half inch to an inch of rainfall, while the north
and central Cascades look to pick up between 1-3 inches into
Wednesday. Winds will pick up and remain breezy on Tuesday in the
vicinity of the frontal system and temperatures look to fall
below seasonal norms. Highs on Tuesday are only expected to reach
the mid 50s. Highs on Wednesday will climb a few degrees, but look
to remain below seasonal norms - topping out in the upper 50s to
low 60s on Wednesday.

.LONG TERM /THURSDAY THROUGH SUNDAY/...The weather pattern will
remain rather similar heading into the second half of the week -
and looks to start with a brief drying trend followed by the
return of cooler and showery weather by the weekend. Latest
deterministic and ensemble guidance have come into better agreement
on upper level ridging over the NE Pacific nudging back into the
Pacific Northwest on Thursday. Thursday currently looks to be the
warmest and driest day in the long term, with afternoon highs
climbing into the low to mid 60s for much of the region. This
drier trend looks to remain short-lived, however, as troughing
over the Western US regains its hold late in the week and allows
for additional systems to move into western Washington. As such,
have maintained chances of showers Friday into the weekend for
now. 14

&&

.AVIATION...Flow aloft is north/northwesterly today with an upper
level trough over the region. Scattered showers remain across the
region, mostly through the Cascades and south of the Olympic
Mountains. A few lightning strikes have been observed but are not
frequent nor widespread. Ceilings are largely VFR this afternoon and
remain so through the early evening. Shower/thunderstorm coverage
will also diminish this evening. Models are hinting that some fog
and low stratus development will be possible between 12-15Z Monday.
MVFR ceilings through most of the terminals, with some patchy fog
possible at OLM and PWT are possible tomorrow morning. Fog/stratus
should lift tomorrow morning back to VFR.

Onshore winds will continue along the coast. Winds light and
variable, predominantly northwesterly through the interior this
evening. Winds decreasing tonight to light or calm. Winds pick back
up slowly tomorrow.

KSEA...VFR conditions this afternoon with a cumulus deck. VFR
conditions should continue through this evening, though could be
lower at times if a shower passes over the terminal. There is a
chance for some low stratus development between around 12-18Z
Monday, but confidence in development is low and may remain VFR even
if it does develop. Winds somewhat variable this afternoon, but
should switch to light northerly this evening. Light winds continue
through the evening, going back to southerly overnight and
increasing tomorrow.

LH

&&

.MARINE...Broad high pressure over the NE Pacific will maintain
onshore flow across western WA this week. Winds look to pick up this
afternoon into tonight, particularly in outermost coastal waters,
and potentially into the Strait of Juan de Fuca, where winds could
gust up to 25 kt. As such, the Small Craft Advisory continues through
tonight. A weak surface ridge will build across the region Monday.
The westerly push down the Strait looks more substantial, with
higher probabilities (65-75%) of Small Craft Advisory threshold
winds. A frontal system will pass through on Tuesday. Behind the
front, northwesterly winds will pick up across the coastal waters.
The active pattern looks to continue into late week with the
potential for additional frontal systems to traverse the region.

Seas around 6 ft near shore to 8 ft in the outermost regions. Seas
will decrease to around 4 to 6 ft Monday night before increasing to
8 to 12 ft Tuesday into Wednesday. Waves may be steep with 8 seconds
being the dominant period through this week.

LH

&&

.HYDROLOGY...The daily hydrology discussion has ended until the
start of the next rainy season; it will only be updated as needed.

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...None.
PZ...Small Craft Advisory until 5 AM PDT Monday for Central U.S.
     Waters Strait Of Juan De Fuca-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-East
     Entrance U.S. Waters Strait Of Juan De Fuca.

&&

$$