571
FXUS66 KSEW 112209
AFDSEW

Area Forecast Discussion
National Weather Service Seattle WA
309 PM PDT Tue Jun 11 2024

.SYNOPSIS...Onshore flow will continue for the next several days.
A weak ridge will result in some slight warming on Thursday but
the next weather system will push through the region Friday into
Saturday bringing cooler conditions and good chances for
precipitation. Thunderstorms will be possible across western
Washington Saturday afternoon and evening. Active weather will
continue into next week.

&&

.SHORT TERM /TODAY THROUGH THURSDAY/...A weakening frontal system
pushed through western Washington this morning and brought some
brief precipitation with it. Breezy conditions persist in the wake
of this system but otherwise little additional impact is expected.

Zonal flow will become very weak ridging from Wednesday into
Thursday keeping flow onshore and temperatures mild. Temperatures
will reach the mid-60s to around 70 Wednesday and the upper 60s to
low 70s on Thursday.

.LONG TERM /FRIDAY THROUGH MONDAY/...Things get more interesting
in the long term as a low from the Gulf of Alaska shifts southeast
off the southern BC coast on Friday. At least an initial frontal
system associated with this feature is expected to push across
western Washington during the day Friday. This will bring with it
widespread chances for rain/shower activity.

Confidence begins to fall off a cliff by Saturday with ensemble
members and deterministic models diverging significantly on the
evolution of the low. One end of the spectrum has this feature
splitting into two with part of the system shifting east of the
area fairly quickly and a second part remaining offshore and
deepening before coming on shore early next week. Meanwhile,
others have a slower and slightly more cohesive system moving
across the region over the weekend. Based on cluster analysis, the
latter appears to be the more likely scenario, but even that
comes in differening flavors of timing, trough depth, etc. These
details will be important as a somewhere lies a scenario with
unstable post-frontal conditions and cool upper level temperatures
aloft on Saturday. That scenario could bring us a decent (for
western Washington) chance of thunderstorm activity Saturday
afternoon and evening, particularly associated with the
development of a convergence zone. At this point in time, the NBM
is highlighting upwards of a 25-30% chance of thunderstorms across
the central Puget Sound and at least 15% elsewhere across western
WA. The main threats with thunderstorm activity would be
lightning, heavy rain, and erratic winds. With this uncertainty by
Saturday, confidence in forecast for Sunday and beyond remains
low at this time. The overall pattern suggests that the door will
remain open of additional waves of activity through at least the
first half of next week. -Wolcott-

&&

.AVIATION...A shortwave trough will continue to move off to the east
tonight. Flow aloft is westerly, becoming more northwesterly this
evening. Conditions have generally improved to VFR across the
majority of the TAF sites this afternoon in the wake of the
frontal passage. Satellite shows clouds scattering across the
interior this afternoon, except across portions of Snohomish and
Skagit counties, where convergence has brought the development of
additional cloud cover. This area of convergence does look to
sink southward through this evening and into the overnight period
and could bring ceilings down across portions of the central Sound
at times. Winds remain breezy at the surface in the wake of the
front, but will gradually ease across the region tonight. Conditions
generally look to remain VFR into Wednesday, however latest NBM
probabilistic guidance does show a 25 percent chance of 3000 ft
cigs on Wednesday morning for areas across the central interior.

KSEA...Ceilings remain VFR this afternoon. Weak convergence to the
north could bring lower cigs into the terminal briefly this evening.
Winds remain breezy out of the SW this afternoon, generally persisting
at 15-20 kt with gusts to 25-30 kt at times. Winds will shift to
the N between 00-03Z, decreasing to 8-12 kt tonight. Probabilistic
NBM guidance showing a 25 percent chance of cigs reaching 3000 ft
early Wednesday. 14

&&

.MARINE...Winds will remain breezy, but will gradually subside in
the wake of a frontal passage this afternoon and evening.
Observations show winds along the coastal waters have started to
subside already this afternoon, but show small craft winds
persisting along portions of the Puget Sound waters. With winds
expected to gradually ease over the next 3 hours, have held off
on an SCA issuance for now. Post-frontal westerlies in the central
and eastern Strait have started to pick up this afternoon as
well, where an SCA remains in effect through tonight. Occasional
gusts to gale will be possible at times, though do not expect
gusts to be frequent enough for a gale issuance. SCAs remain in
effect for the coastal waters as seas have started to build
towards 8-10 ft this afternoon and look to approach 9-13 ft by
tonight.

High pressure will build into the coastal waters in the wake of
the front tonight into Wednesday and will bring overall calmer
conditions to the area waters. Onshore flow will continue over the
next several days, with multiple rounds of westerly pushes expected
along the Strait. This could yield additional headlines at times.
Another frontal system looks to move across the waters Friday
into Saturday. Seas look to gradually subside back to 6-8 ft by
Wednesday and look to generally persist within this range heading
into the weekend. 14

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...None.
PZ...Small Craft Advisory until 2 AM PDT Wednesday for Central U.S.
     Waters Strait Of Juan De Fuca-East Entrance U.S. Waters
     Strait Of Juan De Fuca.

     Small Craft Advisory until 5 AM PDT Wednesday for Coastal Waters
     From Cape Flattery To James Island Out 10 Nm-Coastal Waters
     From James Island To Point Grenville Out 10 Nm-Coastal
     Waters From Point Grenville To Cape Shoalwater Out 10 Nm.

     Small Craft Advisory until 8 AM PDT Wednesday for 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.

&&

$$