616
FXUS66 KSEW 190939
AFDSEW

Area Forecast Discussion
National Weather Service Seattle WA
239 AM PDT Sun May 19 2024

.SYNOPSIS...An upper level trough will move east of the region
this afternoon and a weak upper level ridge will give drier and
somewhat warmer conditions on Monday. Another trough will arrive
on Tuesday for a return to cool and unsettled conditions that will
persist for much of the coming week.


&&

.SHORT TERM /TODAY THROUGH TUESDAY/...Showers continue in the
convergence zone early this morning, but these are expected to
wind down later this morning as an upper trough axis shifts
further eastward and low level onshore flow relaxes somewhat.
Northerly flow aloft on the backside of the trough will lead to
drier conditions by afternoon along with gradually clearing skies
toward this evening. With a little additional sunshine, high
temperatures will edge upward a few degrees...though remaining
below seasonal norms.

Weak upper ridging briefly noses into the region tonight into
Monday for a short-lived drying trend. High temperatures will
approach near normal levels for what could be the only day this
week. By Monday night, the next in a series of a troughs will
dig southward out of British Columbia and rain will spread across
the area Tuesday morning. This system continues to look on the
wet side for late May with much of the lowlands likely to pick up
between a half inch to an inch of rainfall and 1 to 3 inches in
the Cascades. Accordingly, temperatures will be knocked down to
well below seasonal levels.

.LONG TERM /WEDNESDAY THROUGH SATURDAY/...An upper level trough
will progress southeastward across the area on Wednesday
maintaining cool and showery conditions across Western Washington.
Looking toward the later half of the week, it seems that we`ll be
stuck in much the same pattern as recent days. Model ensembles
maintain a mean ridge position well offshore with broad troughing
over the Western US. Look for additional systems to dip southward
out of British Columbia that will keep shower chances in the
forecast and temperatures below normal until further notice. 27

&&

.AVIATION...An upper level trough is over the Pac NW today with
onshore flow. Showers this morning are mainly over the central
sound and in the Cascades where there`s low level convergence. The
central sound is also seeing MVFR to IFR conditions. Showers will
mostly linger over the Cascades this afternoon and there`s a
slight chance of thunderstorms over the North Cascades. Showers
will diminish tonight as the trough shifts farther east. The low
level air mass will remain moist overnight with pockets of low-
end VFR conditions. 33

KSEA...Showers with a convergence zone in the vicinity this
morning with MVFR conditions. Winds S around 5 kt becoming more W
to NW around 21z this afternoon (with drier conditions expected).

33

&&

.MARINE...High pressure over the NE Pacific will maintain onshore
flow across western WA this week. Highest wind and waves will be
through the Strait of Juan de Fuca and outer Coastal Waters -
Small Craft Advisories are in effect. A frontal system will cross
the waters on Tuesday with another (weak) system on Friday. 33

&&

.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.

&&

$$