735
FXUS66 KSEW 121009
AFDSEW

Area Forecast Discussion
National Weather Service Seattle WA
309 AM PDT Wed Jun 12 2024

.SYNOPSIS...Zonal flow aloft today with a weak upper level ridge
over the area tonight and Thursday. Low level flow remaining
onshore keeping high temperatures near normal. Cool upper level
low moving out of the Gulf of Alaska will be near the northern
portion of Vancouver Island Friday night. Front spinning out of
the low moving across Western Washington Friday. Low moving over
the area for a cool and unsettled weekend. The low will move east
Monday. Upper level trough over Western Washington Tuesday.

&&

.SHORT TERM /TODAY THROUGH FRIDAY/...Satellite imagery shows skies
clearing over the southern portion of the area with mostly cloudy
skies over the northern portion. With the clearing skies
temperatures have dropped into the lower 40s over the Southwest
Interior. Temperatures over the remainder of the area at 3 am/10z
were in the mid 40s to lower 50s.

Not much going on today. Zonal flow aloft with low level onshore
flow. Clouds over the northern portion of the area will eventually
scatter out. Even with the sunshine low level onshore flow will
keep highs only in the 60s.

Weak upper level ridge building over Western Washington tonight in
response to a large cool upper level low beginning to move
southeast out of the Gulf of Alaska. It will be cool morning for
June with the lack of cloud cover overnight. Lows mostly in the
40s with the coldest locations dropping into the upper 30s.

Upper level ridge over Western Washington Thursday for another dry
day. Continuation of the low level onshore flow will keep highs
in the 60s and lower 70s even with plenty of sunshine.

Upper level ridge well to the east by later Thursday night. Upper
level low continuing to move southeast and by late Friday will be
near Vancouver Island. Front spinning out of the low moving
through Western Washington Friday with showers likely along the
coast and over the higher terrain with a chance of showers in the
lowlands. Highs will cool back into the upper 50s to mid 60s.

.LONG TERM /SATURDAY THROUGH TUESDAY/...The title of the extended
forecast could be Juneuary returns. Extended models remaining
consistent with the upper level low moving over Western Washington
Saturday and hanging around the area Sunday. If anything the
models are starting to indicate the low might hang around a little
longer into Sunday night/Monday morning. Cool showery weather
both days over the weekend with highs in the mid 50s to lower 60s.
Air mass aloft very cool with 500 mb temperatures -25C to -29C.
Lapse rates plus 7C to 8C and lifted indexes at or below 0. Chance
of thunderstorms already in the forecast for Saturday. Have added
a slight chance for thunderstorms to the forecast for Sunday
afternoon and evening. Low drifts away to the east Monday but not
far enough to eliminate the threat of wrap around moisture making
its way back into Western Washington for a chance of showers.
Weak upper level trough over the area Monday night into Tuesday
keeping a chance of showers in the forecast. Highs Monday in the
mid 50s to lower 60s, Tuesday lower to mid 60s. Felton

&&

.AVIATION...Westerly winds easing aloft as zonal flow to weak
ridging returns. VFR conditions across western Washington with a
broken low-level deck at around 4500 ft. This deck will hang around
through this morning then begin to break up after sunrise.
With decent subsidence aloft, this deck could lower, or some shallow
thin fog could develop in areas under clear skies right around
sunrise. Probabilities of this occuring are fairly low (less than 20-
30% region-wide). Mostly clear skies expected tomorrow and tomorrow
night with only a few passing high clouds.

Light NE winds will become more northerly tomorrow and pick up to
around 8 to 12 kt before easing again tomorrow night.

KSEA...VFR conditions this morning with a BKN045 deck. This cloud
deck will remain through the morning, with some scattered lower
clouds possible. VFR conditions continue through the TAF period with
cloud cover giving way late morning to mostly clear skies through
the evening. Winds NE becoming N later this morning and increasing
to 8 to 12 kt. Winds decrease tomorrow evening and turn back to NE.

LH

&&

.MARINE...Winds are beginning to subside across the region this
morning as a surface ridge begins to build offshore. Breezy winds
continue through the Central and East Strait of Juan de Fuca with
occasional gusts up to 25 kt between Race Rocks and Whidbey Island,
but this will continue to ease through the morning, allowing the
Small Craft Advisory to expire. Winds will increase a bit tonight
along the coastal waters south of Point Grenville as the surface
ridge continues to nose into the region, contrasting with a surface
trough over northern California into Oregon, which will warrant a
short-fused Small Craft Advisory late this afternoon into early
tonight.

High pressure will ease Thursday as a frontal system approaches the
coastal waters on Friday into Saturday. Onshore flow will continue
with several pushes down the Strait of Juan de Fuca during the
evening on Thursday, Friday, and Saturday, each of which may warrant
additional Small Craft Advisories for these time periods.
Uncertainty exists about the forecast into early next week, but the
active pattern may continue.

Combined seas 10 to 11 ft this morning will continue to subside,
allowing the Small Craft Advisory currently in effect for all the
coastal waters to expire later this morning. Seas will subside to 5
to 7 ft later today and remain in that range through the rest of the
week and into the weekend.

LH

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...None.
PZ...Small Craft Advisory until 8 AM PDT this morning for Coastal
     Waters From Cape Flattery To James Island 10 To 60 Nm-
     Coastal Waters From Cape Flattery To James Island Out 10 Nm-
     Coastal Waters From James Island To Point Grenville 10 To
     60 Nm-Coastal Waters From James Island To Point Grenville
     Out 10 Nm-Coastal Waters From Point Grenville To Cape
     Shoalwater 10 To 60 Nm-Coastal Waters From Point Grenville
     To Cape Shoalwater Out 10 Nm-Grays Harbor Bar.

     Small Craft Advisory from 5 PM this afternoon to 1 AM PDT
     Thursday for Coastal Waters From Point Grenville To Cape
     Shoalwater Out 10 Nm.

&&

$$