242
FXUS66 KSEW 191622
AFDSEW

Area Forecast Discussion
National Weather Service Seattle WA
922 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/...Radar shows showers
continuing across the north and central Sound and portions of the
Cascades this morning, but these are expected to wind down
through the day as an upper trough axis shifts further eastward
and low level onshore flow relaxes somewhat. Forecast largely
remains on track this morning, with only a few updates made to
the POPs to account for current radar trends. The previous
discussion follows below, with updates made to the aviation and
marine sections. 14

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...Flow aloft is north/northwesterly today with an upper
level trough over the region. A few light showers remain across the
Pacific coast, the north interior, and the remnants of a
convergence zone east of Seattle. Ceilings are VFR except MVFR
through the central Puget Sound around the Seattle terminals in
association with the decaying convergence zone. Showers will mostly
linger over the Cascades this afternoon and there`s a slight chance
of thunderstorms over the North Cascades. A return to widespread VFR
conditions is expected going into this afternoon with diminishing
cloud cover over the terminals. Showers will diminish tonight as the
trough shifts farther east. A few patches of fog cannot be ruled out
tomorrow morning.

KSEA...Lingering MVFR ceilings this morning in association with a
decaying convergence zone. Winds S around 5 kt becoming more W to NW
around 21z this afternoon (with drier conditions and a return to VFR
ceilings). A return to light southerly winds and partly cloudy (VFR)
skies tonight.

LH

&&

.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. Waves
may become steep with short period waves dominating.

33/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.

&&

$$