126
FXUS66 KSEW 240331
AFDSEW

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

.UPDATE...Clouds continue this evening across an area of weak
convergence over northern King, Snohomish, and Skagit counties, as
well as over the mountains. Lingering moisture may bring light
rain at times in the convergence zone area tonight, with minimal
QPF amounts. Otherwise, patchy fog may be possible in areas of
clearing in Monday morning. No major updates this evening.

&&

.SYNOPSIS...Troughing will slowly slide out of the area on Monday
with ridging building into the Pacific Northwest. Onshore flow
will keep a few clouds along the coast, with most areas
maintaining dry conditions and warming temperatures through
Tuesday. Another 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 THURSDAY/...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 /FRIDAY THROUGH MONDAY/...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 a good portion of western Washington under
cloud cover this evening. VFR ceilings for most terminals. 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/McMillian

&&

.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 have built over the coastal waters around 5 to 8 ft.
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.
&&

$$