879
FXUS66 KSEW 111527
AFDSEW

Area Forecast Discussion
National Weather Service Seattle WA
827 AM PDT Tue Jun 11 2024

.SYNOPSIS...Upper level trough moving through Western Washington
today. Zonal flow aloft tonight into Wednesday with a weak ridge
of high pressure building Wednesday night into Thursday. Cool
upper level low moving southeast out of the Gulf of Alaska late
in the week. System spinning out of the low moving through Friday
with the low overhead for the weekend. The low will move
southeast Monday.

&&

.UPDATE...A weak frontal system is moving east across the region
this morning producing some light rain showers. Minor updates were
made to the forecast to account for the latest trends and short
range forecasts. Impacts will be mainly limited to areas of wet
roadways. The rest of the forecast is on track and no further
updates are expected. -Wolcott-

&&

.SHORT TERM /TODAY THROUGH THURSDAY/...Satellite imagery shows
upper level trough with a weak cold front just offshore early this
morning. Mostly cloudy skies west of Puget Sound. Partly cloudy
skies east of Puget Sound. Temperatures at 3 am/10z were in the
50s.

Upper level trough and the weak front moving through Western
Washington this morning. Satellite imagery shows cloud top
temperatures not cold at all with the front. A good indicator
that there will be little in the way of precipitation with the
system. Best chances for showers this morning over the northern
portion of the area. It will get breezy near the Strait of Juan de
Fuca later this morning into the afternoon hours with increasing
low level onshore flow behind the front. Weak convergence zone
developing over Snohomish county will keep skies more cloudy there
than the rest of the area this afternoon with maybe a light
shower. Highs today a little below normal, in the 60s.

Zonal flow aloft behind the front tonight into Wednesday. Light
flow in the lower levels will keep the morning cloud cover from
being very widespread. Even with the sunny skies, the air mass
over the area is not very warm and what little flow there is in
the lower levels is onshore. Highs Wednesday again the in the
60s. Lows tonight will be a little cool over the Southwest
Interior, lower 40s, with mid to upper 40s for the remainder of
the area.

Weak upper level ridge building Wednesday night into Thursday in
response to a large cool upper level low beginning to move
southeast out of the Gulf of Alaska. Low level flow remaining
onshore. 500 mb heights peaking only in the mid 570 dms. Thursday
looks to be the warmest day in the next week with highs in the
mid 60s to mid 70s. Lows Wednesday night in the 40s.

.LONG TERM /FRIDAY THROUGH MONDAY/...Extended models continuing to
be consistent showing large cool upper level low approaching
Western Washington Friday with the low moving overhead for the
weekend. Weak front spinning out of the low moving through Friday.
Right now Saturday looks to be the coolest and wettest day with
the low right on top of the area. There is a 20 to 30 percent
chance highs Saturday don`t get out of the 50s, over 10 degrees
below normal. Low starts to drift southeast Sunday with the flow
aloft becoming northeasterly. This could help reduce the amount of
showers for Father`s Day especially in the afternoon.
Temperatures will remain cool with highs only in the upper 50s to
mid 60s. Upper level low moving off to the east Monday with a weak
broad upper level trough over Western Washington keeping a chance
of showers in the forecast and highs below normal, in the 60s.
Felton

&&

.AVIATION...Increasing westerly flow aloft ahead of an incoming
shortwave trough. Conditions are mostly VFR across the area
terminals this morning as a frontal system traverses the region,
though a few spots of MVFR and IFR persist along the coast and
southern interior. Latest radar shows showers moving across the
interior this morning for some light rain. Widespread MVFR to
occasional IFR conditions are expected along the coast through the
morning, with high- end MVFR to VFR expected for terminals in the
interior. Ceilings will lift some this afternoon, with breaks in
the clouds possible by this evening. Weak post-frontal convergence
over southern Snohomish County does look to develop and move southward
and could keep ceilings locally lower across the central Sound
through this evening into the early overnight hours. Stratus looks
to redevelop across the interior overnight, however expect conditions
to remain VFR for now.

S/SW winds persist at 10-15 kt across the region, with gusts up
to 25 kt at times as the front moves through. Winds will switch
to northerly through the interior this afternoon in association
with the westerly push through the Strait and remain northerly
through the remainder of the TAF period, through decreasing to 6
kt or less this evening.

KSEA...Ceilings remain primarily VFR this morning, though may dip
down into MVFR with light rain at times as the front moves through.
Cloud cover should break up this afternoon, though weak convergence
north of the terminal may keep ceilings locally lower at times
this evening and will likely keep ceilings from completely clearing
out. Winds S/SW winds up to around 10 to 15 kt, with gusts to 20
to 25 kt possible. Winds will shift to the N this afternoon
between 00-03Z, then decrease this evening.

LH/SB

&&

.MARINE...Increasing southerly winds across the coastal waters early
this morning as a weak frontal system traverses the region today.
Winds will reach Small Craft Advisory criteria across the coastal
waters briefly this morning, as well as through the northern-most
portions of Puget Sound. Following the frontal passage this afternoon
and into tonight, west winds will push through the Strait of Juan
de Fuca and into the northern portions of Admiralty Inlet at times,
permitting additional Small Craft Advisories through late tonight.
Onshore flow will continue through the end of the week and into
the weekend. Another frontal system will move through the region
Friday and Saturday. Several rounds of westerly pushes down the
Strait of Juan de Fuca are expected through this time period, some
of which may require additional headlines.

Seas 4 to 6 ft will build up to 12 to 15 ft by tonight, allowing the
SCA to continue through Wednesday morning for the coastal waters.
Seas remain at around 6 to 8 ft through the end of the week and into
the weekend.

LH

&&

.CLIMATE...High temperatures below 60 in Seattle are infrequent
the last half of June with 40 occurrences in 79 years of records
at Seattle-Tacoma airport. Almost half of them, 17, occurred in
the first 20 years. We have had a high below 60 in the last half
of June in Seattle the last two years, both on June 17th. Last
year the high on the 17th was 59 and in 2022 it was 57. In July
there have only been 15 days with highs less than 60 degrees. The
high of 58 on July 3rd in 2022 was the only time it has occurred
in the last 20 years. Highs in the 50s are even rarer in August
with only 9 occurrences at Seattle-Tacoma airport. Felton

&&

.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.

     Small Craft Advisory from 11 AM this morning to 2 AM PDT
     Wednesday for East Entrance U.S. Waters Strait Of Juan De
     Fuca.

     Small Craft Advisory from 11 AM this morning to 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.

&&

$$