569
FXUS66 KSEW 200348
AFDSEW

Area Forecast Discussion
National Weather Service Seattle WA
848 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/...Forecast remains on
track this evening with just a few lingering showers remaining on
radar. These will continue to taper this evening. No additional
updates, with the remainder of the previous short term discussion
following.

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...North to northwesterly flow aloft with an upper ridge
briefly building offshore. Drier conditions this evening will
continue through Monday. SKC with VFR mid clouds in some areas this
evening, with patchy MVFR cigs along the coast. Cigs will remain SKC
to SCT for most of the interior through early tonight. Cigs will
begin to lower further along the coast tonight and likely stratus
developing into the interior Monday morning with weak onshore flow.
MVFR cigs generally expected with the stratus, however, areas of IFR
cigs may be possible. In addition patchy fog or LIFR cigs may occur
across the Southwest Interior, particularly near KSHN and KPWT.
Otherwise, VFR SCT/BKN cigs expected in the afternoon, with
lingering high end MVFR to low end VFR along the coast. West to
northwest winds at the surface will become light tonight, increasing
again midday Monday.

KSEA...Mostly clear into tonight with VFR cigs. Stratus may develop
late tonight into Monday morning (mainly 12-18z) for MVFR cigs. The
potential for IFR cigs remains rather low with probabilities around
10%. Cigs will improve midday Monday with SCT/BKN VFR cigs into the
afternoon. W/NW winds this evening will become light S/SW
later tonight into Monday. JD

&&

.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-East Entrance U.S. Waters
     Strait Of Juan De Fuca.

     Small Craft Advisory until 11 AM PDT Monday 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.

&&

$$