271
FXUS66 KSEW 230327
AFDSEW

Area Forecast Discussion
National Weather Service Seattle WA
827 PM PDT Sat Jun 22 2024

.UPDATE...A weak front continues to bring light rain to the coast
this evening. Light rain will increase at times for Snohomish
County northward into Sunday, as well as light precipitation for
the Cascades and Olympic Peninsula. Otherwise, cooler temperatures
Sunday.

&&

.SYNOPSIS...A frontal system will bring a few showers across the
region into Sunday, primarily in northwestern Washington. The
onshore flow will also lead to cloudier and cooler conditions for
Sunday. Mix of clouds and sun will be around until another weak
disturbance passes through for Thursday with the chance of
showers. Temperatures will remain relatively cool and slightly
below average for the first full week of summer in Western
Washington.

&&

.SHORT TERM /TONIGHT THROUGH WEDNESDAY/...Satellite this afternoon
shows quite a bit of cloud cover continuing to roll in ahead of an
upper level low/trough, and surface cold front this afternoon.
With the sky coverage quite thick, the mostly clear skies this
afternoon were taken out, filled in with 60-70 percent sky
coverage for the afternoon. There still may be a few peaks of sun
and blue sky here and there, but with the system approaching from
the west, the ceilings will gradually begin to lower going into
late tonight and Sunday. Temperatures for Saturday afternoon have
struggled to climb due to the cloud cover. Highs were lowered into
the low to mid 70s for all interior areas. The warmest spots
today will be in the southwest interior (where clearing of the
cloud coverage was greatest). Additionally, relative humidity
(RH) values have not dropped as much with the cloud coverage
(ranging from around 30 to 55 percent). Few gusty southwest winds
to 20 mph are possible this afternoon ahead of the front, but
otherwise, fire concerns have decreased with the increase of cloud
coverage.

The cold front/upper level low comes through western Washington
late tonight into Sunday. A few sprinkles have formed ahead of
this front (which is still off the Washington coast), but more
showers will increase along the coast and north of Everett late
tonight into Sunday. These will dissipate by late Sunday
afternoon/evening (but may linger around the Snohomish County area
if a post-frontal convergence zone develops). Amounts will remain
light (few hundredths to over a tenth of an inch of QPF). Behind
the front, winds will become light out of the west, and high
temperatures will struggle to get out of the 50s (few low 60s in
urban areas).

Monday and Tuesday will see an upper level ridge move over the
region, which will dry out the region. With onshore flow
remaining through most of the period, will likely still see some
clouds in the morning Monday/Tuesday (particularly on the coast),
with partial clearing taking place later in the afternoon.
Temperatures will return into the 70s by Tuesday, with winds
remaining light. Heat risk concerns remain none or yellow (in
urban areas).

.LONG TERM /THURSDAY THROUGH SUNDAY/...The upper level ridge is
expected to slide eastward Wednesday into Thursday, with a trough
coming in behind it for Thursday. As a result, expect Wednesday to
have more cloud coverage, continuing into Thursday. Showers will
be possible with the disturbance passing through Thursday into
part of Friday. At this time, the threat for thunder is low and
precipitation amounts are expected to remain light. Ensembles
appear to favor keeping western Washington in the clear behind
this system next Saturday into next week. Temperatures will still
remain in the 70s (with Thursday being the coolest day with highs
predominately in the 60s). Winds will remain light at 5 to 10
mph.

HPR

&&

.AVIATION...Southwesterly flow aloft will persist across western
Washington into Sunday as an upper level ridge shifts further to
the east and an upper level trough approaches the region offshore.
Flow aloft will increase tonight into Sunday. In the lower levels,
light onshore flow will gradually increase tonight.

Mid to high level clouds continue to stream overhead the region this
afternoon as a weak frontal system moves inland. Low clouds are
currently observed along the coast. Conditions are VFR across most
area terminals this afternoon. Expect ceilings to maintain around
IFR, 500-1000 feet, along the coast tonight. Conditions along the
coast could even dip to LIFR at times. Across the interior, expect
ceilings to lower down to MVFR, 2000-3000 feet, between 06Z-09Z.
MVFR ceilings look to continue into Sunday and look to lift towards
VFR, 3500-5000 feet, again by the late morning.

KSEA...VFR with mid to high level clouds streaming overhead this
evening. Ceilings will lower down to around 2000 feet between 06Z-
09Z Sunday. MVFR ceilings look to continue through Sunday morning,
before lifting back to VFR by late morning. Southwesterly wind
persisting at 8-12 kt into Sunday, with a few gusts to 18-20 kt
possible at times.

&&

.MARINE...A weak front is making its way inland this
evening. Onshore flow will increase behind the front later tonight.
Weak high pressure will then build into the coastal waters in its
wake and interact with lower pressure inland Sunday through
Tuesday. Another system will move across the area waters Wednesday
into Thursday.

With onshore flow increasing, expect small craft westerly winds
in the Central and Eastern Strait of Juan de Fuca to increase
tonight and to continue into Sunday morning.

Seas continue to hover around 3 feet today and will build toward
6-8 feet Sunday as a larger westerly wave group arrives. Seas
will then subside back towards 5-7 feet Monday and 2-4 feet near
midweek.

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...None.
PZ...Small Craft Advisory until 5 AM PDT Sunday for Central U.S.
     Waters Strait Of Juan De Fuca-East Entrance U.S. Waters
     Strait Of Juan De Fuca.

&&

$$