425
FXUS66 KSEW 232139
AFDSEW

Area Forecast Discussion
National Weather Service Seattle WA
239 PM PDT Sun Jun 23 2024

.SYNOPSIS...An upper level trough continues to keep clouds in the
region this afternoon, as well as a few lingering showers. The
trough will fill over the states overnight into Monday, and will
be replaced with high pressure and upper level ridging. While
onshore flow will keep a few clouds along the coast, most areas
will see dry and mostly clear skies for the first couple days of
the work week, allowing for highs to climb into the upper 70s and
low 80s by Tuesday. One more weak disturbance will pass through
Wednesday and Thursday, returning the chance of showers, and
near normal temperatures for all of western Washington.

&&

.SHORT TERM /TONIGHT THROUGH WEDNESDAY/...Upper level 300 mb
analysis shows an upper level low positioned over west central
B.C. Canada, with a trough digging down into Washington and
Oregon. Dynamically speaking (in terms of vorticity and jet streak
energy), there has been enough support for cloud coverage and a
few showers across the region this morning and afternoon. With
last night`s weak cold front (now a surface trough) east of the
Cascades, there will be a potential for convergence zone showers
across Snohomish/King County border area this afternoon and
evening. These are expected to remain light. Highs today remain
quite a bit below average (by 5 to 10 degrees for some areas),
with temperatures not expected to climb much past 60.

Overnight, the trough will fill in over the region, becoming more
of a zonal onshore flow pattern for the first part of Monday.
There will likely be a mix of low stratus clouds, or potentially
patchy fog in some areas, especially along the coast (depending on
how much clearing there is Monday morning). Otherwise, models pick
up on high pressure building via an upper level ridge, that will
pass inland late Monday into Tuesday. The high temperatures will
still be close to average for Monday (upper 60s to low 70s), but
with models hinting at skies being a lot clearer for Tuesday, many
areas will see highs soaring from the mid 70s to the low 80s for
urban areas. Heat risk remains yellow (minor) with a couple tiny
pockets potentially reaching orange (moderate). With winds
remaining relatively light, this may make it harder to cool off
(if working outdoors).

The pattern will return to unsettled by Wednesday as an upper
level trough will swing into western Washington. This is expected
to be accompanied by an occluded/cold front down at the surface.
Shower chances will increase during the day Wednesday. Depending
on how cool aloft the air gets, will have to watch for a few
isolated thunderstorms (at this point the risk remains in the
northeast Cascades). A few gusty winds 15 to 20 mph are possible
Wednesday afternoon. Temperatures will drop into the mid and upper
60s on Wednesday.

.LONG TERM /THURSDAY THROUGH SUNDAY/...Shower chances continue
into Thursday from the system on Wednesday. With models showing
the system moving through a little bit quicker, the showers may be
wrapped up by Thursday afternoon. There is a little bit of
uncertainty from Friday through Sunday on how much ridging will
take place behind the trough. Looking ahead, it appears Friday
will be the driest day in this period, with another trough
bringing a chance of showers Saturday night through Sunday.
Onshore flow will keep temperatures seasonal.

HPR

&&

.AVIATION...Upper level trough over Western Washington will move
east tonight. Zonal flow aloft tonight and Monday. Onshore flow
will persist in the lower levels through Monday.

Satellite imagery shows much of western Washington under cloud
cover this afternoon, with radar showing some light showers along
the coast, southwest interior, and areas north of KPAE. Ceilings
at the majority of the area terminals have rebounded to VFR. High-
res guidance continues to indicate weak convergence zone showers
persisting over northern King and Snohomish counties this evening
into Monday, which could bring localized MVFR to IFR ceilings to
KPAE at times. Ceilings look to lower towards more widespread MVFR
overnight into early Monday, however look to scatter and lift for
VFR conditions near 18Z Monday.

KSEA...VFR ceilings through tonight. NBM guidance has a 35 percent
chance of MVFR ceilings developing at the terminal between 12-15Z
Monday. High-res guidance indicating CZ showers will likely stay
to the north of the terminal. Southwest wind persisting at 10-14
kt, with gusts to 20-25 kt possible at times into this evening.
Winds will ease back to 4-8 kt after 03Z and look to transition to
the north and increase to 5-10 kt between 18-21Z Monday. 14

&&

.MARINE...Weak high pressure will build back over the coastal
waters and interact with lower pressure inland tonight through
Tuesday. Another frontal system will move across the area waters
on Wednesday. High pressure will then rebuild over the coastal
waters Thursday before another system approaches over the weekend.

Diurnal westerly pushes are expected through the Strait of Juan
de Fuca the next several days and could result in small craft
advisories for the Central and Eastern Strait Tuesday through
Thursday in the evenings.

Seas building to 5-8 feet over the coastal waters this afternoon.
Seas will continue to range between 6-8 feet on Monday, before
subsiding back towards 4-6 feet Monday night into Tuesday. Seas
then look to hover in this range through much of the week. 14

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...None.
PZ...None.
&&

$$